Koosakulnirand, Sirikamon ¹ ; Rajasegaran, Praveena ² ; Alkathiry, Hadil A. ³ ; Chaisiri, Kittipong ⁴ ; Round, Philip D. ⁵ ; Eiamampai, Krairat⁶ ; Khusaini, Mohd K. S. Ahmad ⁷ ; Ramji, Mohamad Fizl Sidq ⁸ ; Abubakar, Sazaly ⁹ ; Ya’cob, Zubaidah ¹⁰ ; Stekolnikov, Alexandr A. ¹¹ and Makepeace, Benjamin L. ¹²

¹Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK & Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
²Tropical Infectious Diseases Research and Education Centre, Universiti Malaya, Kuala Lumpur, Malaysia & Institute for Advanced Studies, Universiti Malaya, Kuala Lumpur, Malaysia.
³Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK & Department of Biology, College of Science, Imam Muhammad bin Saud Islamic University, Riyadh, Saudi Arabia.
⁴Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
⁵Department of Biology, Faculty of Science, Mahidol University, Bangkok, Thailand.
⁶Department of National Park Wildlife and Plant Conservation, Ministry of Natural Resources and Environment, Bangkok, Thailand.
⁷Wildlife Conservation Division, Department of Wildlife and National Parks Peninsular Malaysia, Ministry of Natural Resources, Environment and Climate Change, Malaysia.
⁸Faculty of Resources Science and Technology, University Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia.
⁹Tropical Infectious Diseases Research and Education Centre, Universiti Malaya, Kuala Lumpur, Malaysia.
¹⁰Tropical Infectious Diseases Research and Education Centre, Universiti Malaya, Kuala Lumpur, Malaysia.
¹¹✉ Laboratory of Parasitic Arthropods, Zoological Institute of the Russian Academy of Sciences, Saint Petersburg, Russia.
¹²Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK.

2023 - Volume: 63 Issue: 4 pages: 1109-1138

ZooBank LSID: 87D3BA72-58AE-4CD9-AB4D-4A858244F718

Original research

Keywords

Abstract

Introduction

Southeast Asia is one of the best-studied regions of the world about the taxonomy of chigger mites. The leading countries of this region are Malaysia, with 202 recorded chigger species, and Thailand, with 156 species (Stekolnikov 2021a). However, the chigger species specific to some groups of hosts, such as bats or birds, are under-explored even in such territories. In general, extensive investigations focused on bird chiggers are rare, as compared with chiggers from mammals (Trnka et al. 2022). Among the recent works on Southeast Asian chiggers, a paper based on the collections from Vietnam should be consulted (Kaluz et al. 2016), in which three species of Neoschoengastia Ewing, 1929 (including two new to science), Odontacarus audyi (Radford, 1946), Helenicula scanloni (Domrow & Nadchatram, 1964), Neotrombicula elegans Schluger, 1966, and six species of Leptotrombidium Nagayo et al., 1916 were recorded on seven bird species. Noteworthy is that all of them, except for H. scanloni, were unknown previously in Vietnam, even though this country is the third most studied for chiggers in Southeast Asia, after Malaysia and Thailand (Stekolnikov 2021a).

Our collections performed over the timeframe of 2020 – 2022 obtained a large number of chiggers from birds across Thailand and Malaysia (1,531 individual hosts of 65 species), including one new trombiculid species and a series of unexpected new geographic and host records. Here, we provide a list of these chigger-host records compared with published data, alongside morphological descriptions of our specimens including one new species and notes on the genus Neacariscus and its constituent subgenera. The purpose of this work is to serve as the foundation for quantitative ecological studies of bird-chigger relationships in Southeast Asia that will be presented in a separate publication; thus, we limit our discussion to qualitative findings in the current study.

Material and methods

Approvals for bird sampling

In Peninsular Malaysia, the animal handling work was subjected to the approvals and guidelines from the Universiti Malaya Institutional Animal Care and Use Committee (Permission No: G8/07052020/09012020-01/R), and a wildlife research permit was obtained from the Department of Wildlife and National Parks (DWNP, Permit No. W-00064-15-21). Separate permits were obtained from the Sarawak Forest Department, National Parks and Nature Reserves, East Malaysia (Permit No. SFC.810-4/6/1 – 033 for collection of biological resources and Permit No. WL 13/2022 for permission to enter parks). In Thailand, the study was approved by the Faculty of Tropical Medicine Animal Care and Use Committee (FTM-ACUC, Certification No. 011/2020E) and the Department of National Park Wildlife and Plant Conservation (DNP), Ministry of Natural Resources and Environment (permission letter No. 0907.4/21997). The study was also approved by the Animal Welfare and Ethical Review Body of the University of Liverpool with reference nos. AWC0219 (Malaysia) and AWC0179 (Thailand).

Study sites and bird trapping

Bird trapping was conducted across eight provinces of Thailand (Nan, Nakhon Sawan, Kanchanaburi, Samut Sakhon, Phetchaburi, Rayong, Trang, and Satun) and seven states of Malaysia (Selangor, Pahang, Terengganu, Kedah, Perak, Johor, and Sarawak). Precise sampling locations are listed in Tables 1 and 2, with GPS coordinates provided in the Results. Names of birds follow the IOC World Bird List (Gill et al. 2023). Each location was sampled for 1 – 6 days in proportion to the scale of the site and bird abundance, and some locations were sampled on more than one occasion. Multiple strategies were applied to the capture of different bird species, with expert assistance from DWNP in Malaysia and DNP in Thailand. Passeriformes, Coraciiformes, Piciformes, Podargiformes, Strigiformes, Gruiformes, and Cuculiformes were trapped using mist nets, which were checked every 15 to 20 minutes depending on the abundance of birds in the area of deployment. In Malaysia, Galliformes were captured using large scoop nets at night from 20:00 h to 00:00 h; whereas in Thailand, domestic chickens (only sampled in Ban Huai Muang village, Nan province) were brought by their owners for examination by the field team. Finally, waders (Charadriiformes) in Thailand were captured by cannon netting at diurnal high-tide roosts. In Thailand, birds were identified concerning Treesucon and Limparungpatthanakij (2018) and Lekagul and Round (1991); whereas in Malaysia, the key reference work was Robson (2018). After examination, wild birds were released in the site of capture; domestic birds were returned to the owners.

Chigger collection and examination

Trapped birds were handled gently during examination for the presence of chigger mites. Chiggers attached to the birds were removed carefully using fine forceps and placed in tubes containing 70% ethanol. These were labelled individually according to the number assigned to each of the bird hosts.

A survey of free-living chiggers in the environment was also conducted at Ban Huai Muang village after chigger infestations on chickens were confirmed. Briefly, square black plastic plates were deployed on the ground in a formation of six grids in different habitats inside and around the village (Kundin et al. 1966). The plates were carefully examined for chiggers within 10 minutes following deployment; the free-living chiggers were removed using a fine paintbrush and transferred into 80% ethanol.

With the aid of a dissecting microscope, ~10 – 20% of chiggers from each host or environmental sample were selected by differences in size and appearance as subsamples representative of the chigger species composition. These were then washed in sterile water to remove ethanol, arranged in a dorsoventral position on a glass slide with a drop of Berlese fluid (TCS Bioscience Ltd, UK), and flattened with a round coverslip. Slides were allowed to dry at room temperature before microscopic examination. Initial identification (usually to subgenus) was performed using a combination of brightfield and autofluorescence microscopy (Kumlert et al. 2018). A list of the material from Thailand is given in Table 1 and from Malaysia in Table 2.

A proportion of the microscope slides was shipped to the Zoological Institute of the Russian Academy of Sciences (ZIN, Saint Petersburg, Russia) and examined by AAS under a Leica DM 2500 compound microscope (Leica Microsystems GmbH, Wetzlar, Germany) using differential interference contrast (DIC). Microphotographs were taken using a Leica DMC 4500 digital camera. Morphological drawings were prepared using a drawing tube. Measurements were taken using an ocular micrometer, on an MBI-3 microscope (LOMO plc, Saint Petersburg, Russia) with phase contrast optics. Identification of chigger mites to species was performed with the use of taxonomic revisions published by Nadchatram (1967a, b), Nadchatram and Traub (1971), Vercammen-Grandjean and Langston (1976), Stekolnikov (2013), and other sources cited below, and also by direct comparison with previously identified specimens from the collection of ZIN. The terminology, abbreviations, and diagnostic formulas are used in the present work following Goff et al. (1982) and Stekolnikov and González-Acuña (2015).

Holotype and paratypes of the new species are deposited in ZIN. Most of the Malaysian material was returned to the Universiti Malaya (UM); the material from Thailand is mainly deposited in the University of Liverpool (UoL).

Results

Genus Neacariscus Vercammen-Grandjean, 1960

Type species — Acariscus pluvius Wharton, 1945, by original designation.

Diagnosis — SIF = 7BS(7B)-N-2-3(2)111.1000; fPp = B/B/NNN or B/N/NNN; fCx = 1.1.(1 – 3); fSt = 2.2(4); scutum trapezoidal, with pronounced anterolateral shoulders, with dense puncta; flagelliform sensilla (trichobothria) branched in distal part, nude, or covered by cilia; eyes 2 + 2, often very large; solenidion (ω) of palpal tarsus rod-like or long and slender; parasubterminala (z) nude.

Remarks — The genus Acariscus Ewing, 1943 was a heterogeneous group. Its type species, Trombicula flui van Thiel, 1930, was synonymized with Eutrombicula batatas (Linnaeus, 1758) by Michener (1946). Thus, Acariscus became a synonym of Eutrombicula Ewing, 1938. Subsequently, Vercammen-Grandjean (1960) described a new genus Neacariscus comprising two subgenera – the nominative, with the type species Acariscus pluvius, and Whartonacarus Vercammen-Grandjean, 1960, with the type species Trombicula thompsoni Brennan, 1953. This work did not include lists of species. Loomis (1966) considered Whartonacarus as a subgenus of Toritrombicula Sasa, Hayashi & Kawashima, 1953; he included in it five species. At the same time, he synonymized Neacariscus with Toritrombicula and placed A. pluvius in the nominative subgenus of the latter. However, Vercammen-Grandjean & Langston (1976) disagreed with that decision and restored the generic status of Neacariscus, with three subgenera – the nominative (one species, A. pluvius), Whartonacarus (eight species), and Loomiscus Vercammen-Grandjean & Langston, 1976 (one species). Brennan & Goff (1977) included Whartonacarus in their key to genera as a genus, without a discussion. Later many authors used this name as generic (Domrow & Lester 1985; Hoffmann 1990; Mertins et al. 2009; Stekolnikov & González-Acuña 2015). However, none of them discussed the status of Neacariscus. We note the following:

1. Both Neacariscus pluvius and all species of Whartonacarus significantly differ from Toritrombicula by a) a trapezoidal scutum with prominent anterolateral shoulders vs. a subrectangular scutum without anterolateral shoulders; b) two-pronged palpal claw vs. three-pronged; c) nude parasubterminala (z) vs. branched; d) presence of mastitarsala. This complex of traits constitutes a difference at the generic level.
2. All species of Whartonacarus differ from N. pluvius by the presence of palpal subterminala (ζ) and by the presence of three genualae I (σ) vs. two. These differences can at most justify the subgeneric status.

Therefore, we follow the system of Vercammen-Grandjean & Langston (1976), which included the genus Neacariscus with three subgenera – Neacariscus, Whartonacarus, and Loomiscus. The latter subgenus includes one species, Neacariscus (Loomiscus) dupliseta (Loomis, 1966), which differs from the species of Neacariscus (Whartonacarus) by the presence of multiple additional nude setae on the genuae of all legs. The subgenus Neacariscus (Whartonacarus) includes the following species: N. (W.) anous (Wharton, 1945), N. (W.) chaetosa (Brennan & Jones, 1961), N. (W.) floridensis (Mertins, 2009) (in Mertins et al. 2009), n. comb., N. (W.) nativitatis (Hoffmann-Sandoval, 1950), N. (W.) oceanica (Brennan & Amerson, 1971), N. (W.) shiraii (Sasa, Kano & Obata, 1952), N. (W.) sulae (Oudemans, 1910), and N. (W.) thompsoni (Brennan, 1953).

Subgenus Neacariscus (Neacariscus) Vercammen-Grandjean, 1960

Type species — Acariscus pluvius Wharton, 1945, by original designation.

Diagnosis — SIF = 7B-N-2-2111.1000; fPp = B/B/NNN; fCx = 1.1.1; fSt = 2.2; flagelliform sensilla (trichobothria) branched in distal part; eyes 2 + 2, of normal size; solenidion (ω) of palpal tarsus long and slender.

Neacariscus (Neacariscus) pluvius (Wharton, 1945)

(Fig. 1A)

Distribution and hosts — This species was described from Bougainville Isl. (Solomon Islands archipelago) and from Guam (Mariana Islands), ex Anous stolidus (L.), Anous tenuirostris (Temminck) (Charadriiformes: Laridae), Pluvialis dominica (Statius Müller) (Charadriiformes: Charadriidae), and Tringa incana (J.F. Gmelin) (syn.: Heteroscelus incanus) (Charadriiformes: Scolopacidae). Loomis (1966) also reported N. pluvius from Ulithi Atoll (Caroline Islands), ex Tringa incana and Sterna sumatrana Raffles (Charadriiformes: Laridae). Here this species is for the first time recorded in Asia (Thailand). Charadrius leschenaultii and Xenus cinereus are new host species.

Material examined — Three larvae (ZIN 17963 – 17965) ex two Charadrius leschenaultii and one Xenus cinereus, THAILAND, Trang province, Samran Beach, 7.201348°N, 99.562105°E and 7.209399°N, 99.557854°E, 17 and 19 March 2021, coll. S. Koosakulnirand.

Subgenus Neacariscus (Whartonacarus) Vercammen-Grandjean, 1960

Type species — Trombicula thompsoni Brennan, 1953, by original designation.

Diagnosis — SIF = 7BS-N-2-3111.1000; fPp = B/B/NNN or B/N/NNN; fCx = 1.1.(1 – 3); fSt = 2.2(4); flagelliform sensilla (trichobothria) branched in distal part, nude, or covered by cilia; eyes 2 + 2, often very large; solenidion (ω) of palpal tarsus rod-like or long and slender.

Neacariscus (Whartonacarus) andamanensis Stekolnikov, n. sp.

ZOOBANK: 67AFED09-1E7B-488C-A95B-AD69A8131720

(Figs 1B, C, 2A–E, 3A, C–E, 4)

Diagnosis

SIF = 7BS-N-2-3111.1000; fPp = B/N/NNN; fCx = 1.1.1; fSt = 2.4; PL > AL ≥ AM; fD = 2H-11(13)-11(10)-(8 – 12)-(7 – 10)+(0 – 3); DS = 42 – 49; V = 64 – 84; NDV = 107 – 133; Ip = 1642 – 1697; eyes 2 + 2, very large; flagelliform sensilla (trichobothria) with few branches in distal part; sensillary bases anterior to level of PL; solenidion (ω) of palpal tarsus long and slender; leg tarsi with multiple sclerite bars. Standard measurements are given in Table 3.

Description of larva

Description of larva [based on holotype (ZIN 17980), three paratypes (ZIN 17983 – 17985) and three additional specimens (ZIN 17976 – 17978)]

Idiosoma (Figures 1B, C, 2A – E) — Eyes 2 + 2, very large; 42 – 49 sharply-pointed dorsal idiosomal setae (including two clearly separated humeral setae) moderately covered with thin barbs; 1^st posthumeral row (C excluding humeral setae) with 11 (in five specimens) or 13 (in two specimens) setae, 2^nd row (D) with 11 (in four specimens) or 10 (in three specimens) setae, 3^rd (E) row with 8 – 12 setae, 4th row (F) with 7 – 10 setae, remaining caudal setae 0 – 3 in number; in holotype, fD = 2H-11-11-10-10; two sternal setae between coxae I and four sternal setae between coxae III; 64 – 84 ventral setae; NDV = 107 – 133.

Gnathosoma (Figure 3C – E) — Cheliceral blade with tricuspid cap; cheliceral base densely punctate; gnathobase (infracapitulum) densely punctate, bears one pair of branched gnathocoxal (tritorostral) setae; galeal (deutorostral) seta nude; palpal claw (odontus) with two prongs, main inner and additional smaller outer; palpal femur, genu, and tibia with puncta; palpal femoral seta thick, covered with long branches; palpal genual and tibial setae thin, nude; palpal tarsus with seven branched setae, nude subterminala (ζ) and very long, pointed, curved tarsala (ω).

Scutum (Figures 1B, 3A) —Trapezoidal, with pronounced anterolateral shoulders, with dense puncta; anterior margin sinuous, lateral margins concave, posterior margin almost straight in middle part and obliquely cut at edges; AM placed at level of AL; sensillary (trichobothrial) bases placed anterior to level of PL (PSB – P-PL = 4 – 10 µm, mean 8); PL > AL ≥ AM; all scutal setae barbed similarly to dorsal idiosomal setae; sensilla (trichobothria) flagelliform, with ca. four branches in distal part.

Legs (Figure 4) — All legs 7-segmented (with divided femur), with one pair of claws and claw-like empodium; leg tarsi with multiple sclerite bars. Leg I: coxa with one branched seta (1B); trochanter 1B; basifemur 1B; telofemur 5B; genu 4B, three genualae (σ), microgenuala (κ); tibia 8B, 2 distal tibialae (φ) in tandem, microtibiala (κ); tarsus 22B, tarsala (ω), famulus (ε) distal to tarsala, subterminala (ζ), nude parasubterminala (z), pretarsala (ζ). Leg II: coxa 1B; trochanter 1B; basifemur 2B; telofemur 4B; genu 3B, genuala (σ); tibia 6B, two tibialae (φ) in tandem; tarsus 18B, tarsala II (ω), famulus (ε) behind tarsala, pretarsala (ζ). Leg III: coxa 1B; trochanter 1B; basifemur 2B; telofemur 3B; genu 3B, long genuala (σ); tibia 6B, long tibiala (φ); tarsus 16B, mastitarsala in middle part of segment.

Type material

Larval holotype (ZIN 17980, BTRA045) ex Calidris tenuirostris, THAILAND, Trang province, Koh Libong, 7.243892°N, 99.451315°E, 16 March 2021, coll. S. Koosakulnirand; four paratypes (ZIN 17983 – 17986) ex four Calidris tenuirostris, THAILAND, Trang province, Samran Beach, 7.209399°N, 99.557854°E, 19 March 2022, coll. S. Koosakulnirand.

Additional material

Three larvae (ZIN 17976 – 17978) ex two Calidris tenuirostris and one Charadrius lechenaultii, THAILAND, Satun province, Thung Sabo, 7.042112°N, 99.671153°E, 14 March 2021, coll. S. Koosakulnirand.

Two larvae (UoL) ex one Calidris tenuirostris, THAILAND, Trang province, Koh Libong, 7.243892°N, 99.451315°E, 16 March 2021, coll. S. Koosakulnirand (same data as for holotype); nine larvae (UoL) ex four C. tenuirostris (6) and two Xenus cinereus (3), THAILAND, Trang province, Samran Beach, 7.209399°N, 99.557854°E, 19 March 2022, coll. S. Koosakulnirand; one larva (UoL) ex Calidris ruficollis, THAILAND, Trang province, Samran Beach, 7.201348°N, 99.562105°E, 15 March 2021, coll. S. Koosakulnirand; six larvae (UoL) ex three C. tenuirostris, THAILAND, Satun province, Thung Sabo, 7.042112°N, 99.671153°E, 14 March 2021, coll. S. Koosakulnirand.

Etymology

The species epithet andamanensis refers to the Andaman Sea, on the shore of which the type locality is situated.

Differential diagnosis

The new species is similar to Neacariscus (Whartonacarus) shiraii but differs from it in exhibiting fewer idiosomal setae (DS = 42 – 49 vs. 77 – 92; NDV = 107 – 133 vs. 162 – 190); the rows of dorsal idiosomal setae are unpaired (only a few additional setae are present posterior to the central part of 1^st row); in its longer scutum with more prominent posterior margin (ASB = 39 – 42 vs. 33 – 36, PSB = 23 – 27 vs. 19 – 21, SD = 63 – 66 vs. 52 – 57, and P-PL = 14 – 20 vs. 11 – 13); and in longer legs (Ip = 1642 – 1697 vs. 1381 – 1550 and TaIIIL = 178 – 189 vs. 160 – 162).

Neacariscus (Whartonacarus) shiraii (Sasa, Kano & Obata, 1952)

(Figs 2F – G, 3B)

Diagnosis — SIF = 7BS-N-2-3111.1000; fPp = B/N/NNN; fCx = 1.1.1; fSt = 2.4; PL > AL ≥ AM (PL > AM > AL); fD = 2H-23-24(20)-18(19)-13(11)-(0 – 2); DS = 77 – 92; V = 85 – 98; NDV = 162 – 190; Ip = 1381 – 1550; eyes 2 + 2, very large; flagelliform sensilla (trichobothria) with few branches in distal part; sensillary bases anterior to level of PL; solenidion (ω) of palpal tarsus long and slender; leg tarsi with multiple sclerite bars. Standard measurements are given in Table 3.

Distribution and hosts — This species was described from Tokyo (Japan), ex Pluvialis dominica (syn.: Charadrius dominicus). Later it was recorded on Heron Isl. (Australia, Queensland), ex Limosa lapponica (L.) (Charadriiformes: Scolopacidae); on Guam, ex P. dominica; on Okinawa Isl. (Japan), ex Sterna dougalli Montagu (Charadriiformes: Laridae); and in Mexico (Sonora), ex Haematopus palliatus Temminck (Charadriiformes: Haematopodidae) (Vercammen-Grandjean & Langston 1976). Here it is for the first time recorded in Thailand and on Xenus cinereus.

Material examined — Two larvae (ZIN 17981, 17982) ex two Xenus cinereus, THAILAND, Trang province, Samran Beach, 7.209399°N, 99.557854°E, 19 March 2022, coll. S. Koosakulnirand.

Remarks — The form of N. (W.) shiraii from Mexico, with DS = 44 and V = 44 (Loomis 1966; Mertins et al. 2009), probably belongs to some other species.

Neacariscus (Whartonacarus) sulae (Oudemans, 1910)

(Fig. 1D)

Diagnosis — SIF = 7BS-N-2-3111.1000; fPp = B/N/NNN; fCx = 1.1.1; fSt = 2.2; PL ≫ AL = AM; fD = 2H-10-10-6-2-2; DS = 32 – 36; V = 50 – 65; NDV = 86 – 101; Ip = 1181 – 1206; eyes 2 + 2, of moderate size; flagelliform sensilla (trichobothria) with short branches in distal part; sensillary bases anterior to level of PL; solenidion (ω) of palpal tarsus long and slender. Standard measurements are given in Table 4.

Distribution and hosts — This species was described from a single specimen (holotype) collected in an unknown locality of West Africa, ex Morus capensis (Lichtenstein) (syn.: Sula capensis) (Suliformes: Sulidae). Zumpt (1961) referred to the host as Morus bassanus (L.). Here it is for the first time recorded in Asia and on Pluvialis squatarola.

Material examined — Two larvae (ZIN 17962, 18168) ex Pluvialis squatarola, THAILAND, Trang province, Koh Libong, 7.243892°N, 99.451315°E, 16 March 2021, coll. S. Koosakulnirand.

Remarks — The species was initially described briefly (Oudemans 1910): a fully illustrated redescription was published two years later (Oudemans 1912). Fuller (1952) and Vercammen-Grandjean & Langston (1976) also examined and redescribed the holotype. According to the latter authors, the fD of the holotype is 2H-8-8-8-4-4-2, which seems different from the fD in our material (2H-10-10-6-2-2). However, a comparison of the drawing made by Oudemans (1912, fig. A1) with our specimens shows that the divergence could be caused by a different mode of preparation and, probably, unequal levels of mite engorgement.

Fuller (1952) described the ventral palpal tibial seta of the holotype as branched, which agrees with the drawing made by Oudemans (1912, fig. A4). However, Vercammen-Grandjean & Langston (1976) drew and described this seta as nude, as in our material. The scutum on their drawing (pl. 282) bears multiple transverse striae, which were not mentioned by Oudemans (1912) and Fuller (1952). They are also absent in our specimens. Therefore, our material may represent a new species close to N. sulae. Additional collections in Africa and one more re-examination of the N. sulae holotype would be desirable to reach a conclusion.

Genus Toritrombicula Sasa, Hayashi & Kawashima, 1953

Type species — Trombicula (Toritrombicula) hasegawai Sasa, Hayashi & Kawashima, 1953, by original designation.

Diagnosis — SIF = 7B-N(B)-3-2111.0000; fPp = B/B/NNN or B/B/NNB; fCx = 1.1.1; fSt = 2.2; scutum subrectangular, without prominent anterolateral shoulders, with puncta; flagelliform sensilla (trichobothria) branched in distal part; eyes 2 + 2, anterior pair often very large; solenidion (ω) of palpal tarsus rod-like; parasubterminala (z) branched.

Toritrombicula densipiliata (Walch, 1922)

Distribution and hosts — Indonesia, Malaysia, Papua New Guinea, Philippines, Taiwan, Thailand, ex 21 bird species (Stekolnikov 2021a). Arachnothera longirostra, Batrachostomus stellatus, Cacomantis sepulcralis, Copsychus malabaricus, Cyanoptila cyanomelana, Cyornis tickelliae, Ficedula dumetoria, Geokichla sibirica, Lanius tigrinus, Larvivora cyane, Malacocincla abbotti, Pellorneum malaccense, Malacocincla sepiaria, Malacopteron cinereum, Malacopteron magnum, Mixornis bornensis, Turdinus macrodactylus, Pellorneum capistratum, Pellorneum ruficeps, Cyornis brunneatus, Cyanoderma erythropterum, Stachyris maculata, Terpsiphone atrocaudata, Tricholestes criniger, and Turdus obscurus are new host species.

Material examined — Two larvae (ZIN 18002, 18003) ex Geokichla citrina and Geokichla sibirica, THAILAND, Rayong province, Koh Mun Nai, 12.612384°N, 101.687574°E, 10 March 2021, coll. S. Koosakulnirand; one larva (ZIN 17935) ex Mixornis bornensis, MALAYSIA, Sarawak State, Sematan Pueh village, 1.831126°N, 109.708966°E, 23 March 2022, coll. P. Rajasegaran.

Five larvae (UM) ex one Pellorneum ruficeps (1), one Cyornis tickelliae (1), two Larvivora cyane (2), and one Malacocincla abbotti (1), MALAYSIA, Kedah State, Langkawi Isl., Gunung Machinchang, 6.429010°N, 99.729852°E, 16 – 17 March 2022, coll. P. Rajasegaran; 41 larvae (UM) ex one Pellorneum nigrocapitatum (1), one Calyptomena viridis (1), one Ficedula dumetoria (3), one Macronus ptilosus (2), one Pellorneum malaccense (2), one Malacocincla sepiaria (1), one Malacopteron cinereum (2), one Malacopteron magnum (1), one Turdinus macrodactylus (1), five Philentoma pyrhoptera (11), two Stachyris maculata (2), three Stachyris poliocephala (12), and one Terpsiphone atrocaudata (1), MALAYSIA, Pahang State, Krau Wildlife Reserve, 3.596982°N, 102.183190°E, 16 – 20 February 2021, coll. P. Rajasegaran; 30 larvae (UM) ex two Actenoides concretus (3), one Arachnothera longirostra (1), one Batrachostomus stellatus (1), five Copsychus malabaricus (11), one Lanius tigrinus (1), two Larvivora cyane (2), three Philentoma pyrhoptera (4), and two Cyornis brunneatus (6), MALAYSIA, Perak State, Behrang Forest Reserve, 3.732175°N ,101.578552°E, 19 – 24 September 2022, coll. P. Rajasegaran; two larvae (UM) ex Anthipes solitaris and Turdus obscurus, MALAYSIA, Perak State, Larut Hill, 4.867858°N, 100.779824°E, 9 – 11 March 2022, coll. P. Rajasegaran; four larvae (UM) ex Calyptomena viridis, Copsychus malabaricus, Cyanoptila cyanomelana, and Philentoma pyrhoptera, MALAYSIA, Sarawak State, Gunung Gading National Park, Lundu, 1.692098°N, 109.845157°E, 23 – 26 March 2022, coll. P. Rajasegaran; one larva (UM) ex Mixornis bornensis, MALAYSIA, Sarawak State, Sematan Pueh village, 1.831126°N, 109.708966°E, 23 March 2022, coll. P. Rajasegaran; one larva (UM) ex Cacomantis sepulcralis and two larvae (UM) ex one Tricholestes criniger, MALAYSIA, Selangor State, Ulu Gombak Forest Reserve, 3.325987°N, 101.752747°E, 10 – 12 February 2021, coll. P. Rajasegaran; seven larvae (UM) ex four Larvivora cyane (4), two Philentoma pyrhoptera (2), and one Stachyris poliocephala (1), MALAYSIA, Terengganu State, Pasir Raja Forest Reserve, 4.790517°N, 102.996835°E, 22 – 27 October 2021, coll. P. Rajasegaran; 33 larvae (UM) ex 11 Copsychus malabaricus, MALAYSIA, Terengganu State, Redang Isl., 5.780867°N, 103.006183°E, 8 – 13 October 2022, coll. P. Rajasegaran.

Toritrombicula kirhocephales Goff, 1982

(Fig. 5A)

Diagnosis — SIF = 7B-N-3-2111.0000; fPp = B/B/NNN; fCx = 1.1.1; fSt = 2.2; PL > AL > AM; fD = 2H-10(11)-8(10)-(6 – 8)-4-2; DS = 32 – 37; V = 26 – 34; NDV = 58 – 68; Ip = 1026 – 1246; eyes 2 + 2, of moderate size; flagelliform sensilla (trichobothria) with short branches in distal part; sensillary bases anterior to level of PL. Standard measurements are given in Table 5.

Distribution and hosts — This species was described ex Pitohui kirhocephalus (R.P. Lesson & Garnot) (Passeriformes: Oriolidae) from Papua New Guinea (East Sepik province). Here it is for the first time recorded in Asia (Thailand) and on all hosts mentioned below.

Material examined — Six larvae (ZIN 18004 – 18009) ex one Larvivora cyane (1), two Pachycephala cinerea (2), one Pycnonotus conradi (1), and one Phylloscopus tenellipes (2), THAILAND, Rayong province, Koh Mun Nai, 12.612384°N, 101.687574°E, 9 – 11 March 2021, coll. S. Koosakulnirand; one larva (ZIN 18010) ex L. cyane, THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.13111°N, 99.14863°E, 10 December 2021, coll. S. Koosakulnirand; two larvae (ZIN 18011, 18012) ex Ficedula albicilla and Pycnonotus conradi, THAILAND, Kanchanaburi province, 5 km NW Mahidol University Campus, 14.15452°N, 99.12069°E, 13 December 2021, coll. S. Koosakulnirand.

19 larvae (UoL) from same localities, same and additional host individuals of the same species plus one larva (UoL) ex Cyornis tickelliae, THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.13111°N, 99.14863°E, 10 December 2021, coll. S. Koosakulnirand; one larva (UoL) ex Pycnonotus aurigaster, THAILAND, Kanchanaburi province, 5 km NW Mahidol University Campus, 14.15452°N, 99.12069°E, 13 December 2021, coll. S. Koosakulnirand.

Remarks — Our specimens deviate from the original description (Goff 1982) in more numerous idiosomal setae (fD = 2H-10(11)-8(10)-8(7)-4-2 vs. 2H-10-8-6-4-2, DS = 34 – 37 vs. 32, V = 31 – 34 vs. 26, NDV = 65 – 68 vs. 58) and slightly longer legs (Ip = 1145 – 1246 vs. 1026 – 1045, TaIIIL = 112 – 121 vs. 98). We estimate this difference as a case of intraspecific variation.

Toritrombicula kirhocephales differs from T. densipiliata in exhibiting fewer idiosomal setae (two humeral setae vs. four; 1^st posthumeral row simple vs. double; DS = 34 – 37 vs. 50 – 65; NDV = 58 – 65 vs. about 104) (Goff 1982; Nadchatram 1967b; Vercammen-Grandjean & Langston 1976).

Toritrombicula uphami Nadchatram, 1967

(Fig. 5B)

Distribution and hosts — Described ex Pitta sordida (Statius Müller) (Passeriformes: Pittidae) in Malaysia. Cyornis tickelliae, Enicurus ruficapillus, and Pellorneum nigrocapitatum are new host species.

Material examined — Two larvae (ZIN 18172, 18173) ex Enicurus ruficapillus and Pellorneum nigrocapitatum, MALAYSIA, Terengganu State, Pasir Raja Forest Reserve, 4.790517°N, 102.996835°E, 24 October 2021, coll. P. Rajasegaran; one larva (ZIN 18169) ex Cyornis tickelliae, MALAYSIA, Kedah State, Langkawi Isl., Gunung Machinchang, 6.429010°N, 99.729852°E, 15 March 2022, coll. P. Rajasegaran.

Genus Neoschoengastia Ewing, 1929

Type species — Schoengastia americana Hirst, 1921, by original designation.

Diagnosis — SIF = 7B(7BS)-B-3-(2–3)111.0(1)000; cheliceral blade with tricuspid cap; scutum trapezoidal, with anterolateral shoulders, covered by puncta and cuticular striations around sensillary bases, with almost straight, concave or bilobate posterior margin; sensillary bases far anterior to PL; usually AL > PL; sensilla pyriform or globose, covered with setules; eyes 2 + 2; parasubterminala (z) branched; onychotriches frequently present.

Neoschoengastia longipes Nadchatram, 1967

(Fig. 5C)

Diagnosis — SIF = 7BS-B-3-3111.0000; fPp = B/B/BNB; fCx = 1.1.3; fSt = 2.2; AL ≥ PL > AM; fD = 2H-6-6-4-6-4-2 (6-6-4-4-6, 6-6-6-6-4, and other similar variants); Ip = 1140 – 1294; DS = 28 – 31; V = 19 – 25; NDV = 50 – 54; onychotriches present on claws and empodium. Standard measurements are given in Table 6.

Distribution and hosts — THAILAND, ex 14 bird species (Stekolnikov 2021a). Alcedo atthis, Calliope calliope, Larvivora cyane, and Otus sunia are new host species.

Material examined — Two larvae (ZIN 17946, 17947) ex Alcedo atthis and Larvivora cyane, THAILAND, Rayong province, Koh Mun Nai, 12.612384°N, 101.687574°E, 9 March 2021, coll. S. Koosakulnirand; six larvae (ZIN 17948 – 17953) ex four Copsychus malabaricus (4), Cyornis tickelliae (1), and L. cyane (1), THAILAND, Kanchanaburi province, SW Mahidol University Campus, 14.11806°N, 99.15253°E, 8 – 9 December 2021, coll. S. Koosakulnirand; one larva (ZIN 17954) ex C. malabaricus, THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.13111°N, 99.14863°E, 10 December 2021, coll. S. Koosakulnirand.

A great many (42) larvae (UoL) from the same localities, same and additional individuals of the same host species, plus 13 larvae ex four C. malabaricus (7), two C. tickelliae (2), and three L. cyane (4), THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.134225°N, 99.1374365°E, 11 December 2021, coll. S. Koosakulnirand; nine larvae (UoL) ex two Calliope calliope (4), one L. cyane (3), and one Otus sunia (2), THAILAND, Kanchanaburi province, NW Mahidol University Campus, 14.154772°N, 99.1193296°E, 12 December 2021, coll. S. Koosakulnirand.

Remarks — Neoschoengastia longipes belongs to the group of species close to N. americana, which is characterized by the presence of three setae on coxa III (fCx = 1.1.3). Nadchatram (1967a) compared N. longipes with Neoschoengastia entomyza Womersley, 1952 and Neoschoengastia thomasi (Radford, 1946). The main difference between N. longipes plus N. thomasi and N. americana is the presence of six setae in the first posthumeral row vs. eight. Our material on N. longipes also differs from two specimens of N. americana collected in Paraguay (Stekolnikov et al. 2022) by NDV = 50 – 54 vs. 61 – 62, AP = 34 – 41 vs. 28 – 31, and AL = 59 – 74 vs. 47. The difference by AL and, to a lesser extent, by AP agrees with the morphometric data on N. americana provided by Domrow (1974). However, the mean values of measurements from Malaysian specimens identified as N. americana by Domrow & Nadchatram (1960) differed from ours. In addition, the specimens examined by Domrow & Nadchatram (1960) were characterized by the presence of two additional sternal setae (fSt = 2.4. vs. 2.2). Probably, they belong to a new and still undescribed species. Neoschoengastia entomyza, a species described from Australia, was synonymized with N. americana by Domrow (1974), but we believe that these two taxa require a more detailed comparison. Thus, the presence of N. americana outside the American continent remains questionable.

Neoschoengastia thomasi was described incompletely, without characters of gnathosoma and legs (Radford 1946). According to the redescription prepared by Nadchatram (1967a) on the base of the type specimen deposited in the British Museum (Natural History), London (currently, Natural History Museum), N. thomasi differs from N. americana and N. longipes by the branched lateral palpal tibial seta (fPp = B/B/BbB vs. B/B/BNB). The redescription was illustrated with a drawing of the scutum lacking all setae except for one AL and one PL (Nadchatram 1967a, fig. 17). Surprisingly, the cuticular striations in the medial part of the scutum were drawn as transverse, whereas they are longitudinal in all above species. As noted by Domrow and Lester (1985), this drawing rather corresponds to Neoschoengastia struthidia Womersley, 1952. Fernandes and Kulkarni (2003) based their redescription of N. thomasi on existing literature. Unfortunately, the size of the N. thomasi type series and the place of deposition of other type specimens is unknown. Therefore, it remains a dubious species.

Among our N. longipes material, three measured specimens (ZIN 17951, 17953, 17954) from Copsychus malabaricus collected 9 – 10 December 2021 differ from five other measured specimens by a lesser NDV (50 vs. 53 – 54) smaller scutum (AW = 46 – 50 vs. 51 – 58; SB = 26 – 28 vs. 29 – 35; SD = 44 – 47 vs. 49 – 56), and shorter legs (Ip = 1197 – 1210 vs 1222 – 1294; TaIIIL = 122 – 128 vs. 131 – 139). We provisionally consider this as a case of intraspecific variability.

Neoschoengastia solitus Nadchatram, 1967

Distribution and hosts — Malaysia, Thailand, ex 11 bird species (Stekolnikov 2021a).

Material examined — Three larvae (ZIN 17955 – 17957) ex one Geokichla citrina, THAILAND, Rayong province, Koh Mun Nai, 12.612384°N, 101.687574°E, 10 March 2021, coll. S. Koosakulnirand.

Neoschoengastia gallinarum (Hatori, 1920)

Distribution and hosts — China, Malaysia, Taiwan, Vietnam, ex 24 bird species and subspecies, and from two species of rats and a hare (Stekolnikov 2021a). Here this species is for the first time reported from Thailand. Argusianus argus, Lophura rufa, and Polyplectron inopinatum are new hosts.

Material examined — Four larvae (ZIN 17958 – 17961) ex one Gallus gallus domesticus, THAILAND, Nan province, Ban Huai Muang village, 19.139995°N, 100.718956°E, 23 December 2021, coll. S. Koosakulnirand; two larvae (UM) ex one Argusianus argus and 14 larvae ex five Polyplectron malacense, MALAYSIA, Johor State, Jemaluang Wildlife Conservation Centre, 2.291356°N, 103.852966°E, 22 February 2022, coll. P. Rajasegaran; 11 larvae (UM) ex five Gallus gallus domesticus, MALAYSIA, Johor State, Kota Tinggi plantation, 2.030233°N, 103.866035°E, 21 – 23 June 2022, coll. P. Rajasegaran; 24 larvae (UM) ex two Lophura rufa (15), three Polyplectron inopinatum (8), and one Polyplectron malacense (1), MALAYSIA, Perak State, Sungkai Wildlife Conservation Centre, 4.064302°N, 101.366232°E, 9 January and 8 March 2021, coll. P. Rajasegaran; nine larvae (UM) ex seven Gallus gallus domesticus, MALAYSIA, Selangor State, Bestari Jaya village, 3.378008°N, 101.410224°E, 12 April 2021, coll. P. Rajasegaran.

Genus Schoengastia Oudemans, 1910

Type species — Thrombidium vandersandei Oudemans, 1905.

Diagnosis — SIF = 7BS-N-3(2)-3(2)111.(0 – 2)000; cheliceral blade serrate on its dorsal edge, with tricuspid cap; scutum usually subpentagonal, with convex posterior margin; AL > PL > AM, sensillary bases situated not far apart and close to level of PLs; sensilla globose, covered with setules; eyes 2 + 2.

Schoengastia archaea (Taufflieb, 1960)

(Fig. 5D)

Diagnosis — SIF = 7BS-N-3-2111.0000; fPp = B/B/NBB; fCx = 1.1.1; fSt = 2.2; AL ≥ PL ≫ AM; fD = (49 – 60)-(26 – 30)+(56 – 72); DS = 138 – 159; V = 89 – 100; NDV = 227 – 254; Ip = 1024 – 1127; cheliceral blade with four dorsal hooks; eyes 2 + 2, very large; scutum as long as wide, with prominent anterolateral shoulders, with greatly projected posterior margin concave in center; entire scutum covered with puncta, its half posterior to sensillary bases also covered with distinct transverse striations; sensilla (trichobothria) drop-shaped, covered with setules; sensillary bases posterior to level of PL; leg tarsi with multiple sclerite bars; S₁ in distal part of segment, f₁ behind S₁, f₂ behind S₂. Standard measurements are given in Table 7.

Distribution and hosts — This species was described from Senegal (Rufisque), ex Sterna hirundo L. (Charadriiformes: Laridae) (Taufflieb 1960). Here it is for the first time recorded in Asia (Thailand) and on all hosts mentioned below.

Material examined — Six larvae (ZIN 17966 – 17971) ex two Charadrius mongolus (2), one Calidris ruficollis (1), two Calidris tenuirostris (2), and one Xenus cinereus (1), THAILAND, Trang province, Samran Beach, 7.201348°N, 99.562105°E and 7.209399°N, 99.557854°E, 15 – 17 March 2021, 19 March 2022, coll. S. Koosakulnirand; four larvae (ZIN 17972 – 17975) ex three Numenius arquata, THAILAND, Trang province, White Dragon Spine Beach (7.2984973°N, 99.420628°E), 20 March 2022, coll. S. Koosakulnirand.

12 larvae (UoL) from the same localities, same and additional host individuals of the same species.

Remarks — This species is similar to Schoengastia galapa Stekolnikov, 2021 described ex marine iguana Amblyrhynchus cristatus Bell (Squamata: Iguanidae) from the Galápagos Islands; this similarity has not been noted before. Both species stand out among Schoengastia due to the numerous idiosomal setae (NDV ca. 200 or more), the presence of two genualae I (σ) vs. three or more, the presence of anterolateral shoulders of the scutum, and the presence of transverse cuticular striations on the scutum posterior to sensillary bases. Such striations do not reach the level of sensillary bases in all other species of Schoengastia (Stekolnikov 2021b). Schoengastia galapa differs from S. archaea by fPp = N(b)/N/NNB vs. B/B/NNB, much shorter legs (Ip = 733 – 795 vs. 1019 – 1127) without additional sclerite bars, presence of mastitarsalae, f₁ distal to S₁ vs. proximal, smaller anterior pair of eyes, fewer idiosomal setae (NDV = 197 – 206 vs. 227 – 256), and by a wider scutum (AW = 46 – 48 vs. 34 – 38, PW = 62 – 66 vs. 51 – 56).

Genus Ascoschoengastia Ewing, 1946

Ascoschoengastia lorius (Gunther, 1939)

Distribution and hosts — Australia, China, Papua New Guinea, Thailand, Vietnam, ex nine mammal hosts and four bird species (Stekolnikov 2021a). Here this species is for the first time recorded in Malaysia and on Meiglyptes tukki.

Material examined — 12 larvae (UM) ex one Meiglyptes tukki, MALAYSIA, Pahang State, Krau Wildlife Reserve, 3.596982°N, 102.183190°E, 17 February 2021, coll. P. Rajasegaran.

Genus Blankaartia Oudemans, 1911

Blankaartia acuscutellaris (Walch, 1922)

Distribution and hosts — Eastern Europe, Spain, Tropical Africa, Central, South, Southeast, and East Asia, mainly on water birds, also on mammals of different orders, including humans, and two records on chameleons (Stekolnikov 2021a). Lewinia striata is a new host species.

Material examined — One larva (ZIN 18170) ex Lewinia striata, MALAYSIA, Sarawak State, Sematan Pueh village, 1.831126°N, 109.708966°E, 22 March 2022, coll. P. Rajasegaran.

One larva (UM) with the same data.

Genus Ericotrombidium Vercammen-Grandjean, 1966

Ericotrombidium cosmetopode (Vercammen-Grandjean & Langston, 1971)

(Fig. 6)

Diagnosis — SIF = 7BS-B-3-2111.0000; fPp = B/B/NNB; fCx = 1.1.1; fSt = 2.2; PL > AL > AM (PL > AM ≥ AL); fD = 2H-8-6-6-4-2 (8-6-6-4-4-2); DS = 28 – 32; V = 27 – 28; NDV = 55 – 60; Ip = 666 – 770; dorsal idiosomal setae tetrapectinate, with thin barbs; scutum with large puncta, with bilobate posterior margin; SB at level of PL; sensilla with cilia in medial part and ca. 13 branches in distal third; f₁ distal to S₁, f₂ distal to S₂; S₂ thin, pointed. Standard measurements are given in Table 8.

Distribution and hosts — This species was described from free larvae found in a ground hole, Malaysia, Selangor State, Ulu Langat Forest Reserve. Pellorneum ruficeps is the first known host of this species.

Material examined — One larva (ZIN 17937) ex Pellorneum ruficeps, MALAYSIA, Pahang State, Fraser's Hill, 3.725630°N, 101.716365°E, 22 October 2021, coll. P. Rajasegaran.

Remarks — As compared with the original description, our specimen has longer legs and a slightly reduced number of idiosomal setae (Table 8).

Genus Eutrombicula Ewing, 1938

Eutrombicula wichmanni (Oudemans, 1905)

Distribution and hosts — Australia, Myanmar, Brunei, China, Guam, Indonesia, Japan, Malaysia, Papua New Guinea, Philippines, Taiwan, Thailand, Vietnam, ex many species of mammals from different orders (including humans), reptiles, and birds (Stekolnikov 2021a).

Material examined — Three larvae (ZIN 17997 – 17999) collected by the black plate technique, THAILAND, Nan province, Ban Huai Muang village, 19.140834°N, 100.718315°E, 26 December 2021, coll. Kamonchanok Bunmee; 19.1391337°N, 100.7195905°E, 25 December 2021, coll. Rawadee Kumlert; 19.1378833°N, 100.7193387°E, 27 December 2021, coll. Kamonchanok Bunmee; two larvae (ZIN 18000, 18001) ex two Gallus gallus domesticus, same place, 19.139652°N, 100.718019°E and 19.140026°N, 100.719794°E, 23 December 2021, coll. S. Koosakulnirand.

A great many (113) larvae (UoL) ex Gallus gallus domesticus, THAILAND, Nan province, Ban Huai Muang village, different collection sites, 23 – 24 December 2021, coll. S. Koosakulnirand; 2 larvae (UoL) ex Gallus gallus domesticus, THAILAND, Nan province, Ban Santisuk village, 19.131006°N, 100.698332°E, 24 December 2021, coll. S. Koosakulnirand.

Genus Helenicula Audy, 1954

Helenicula comata (Womersley, 1952)

Distribution and hosts —China, India, Philippines, ex Rattus tanezumi (Stekolnikov 2021a). Here this species is for the first time recorded in Thailand and on Gallus gallus domesticus.

Material examined — One larva (ZIN 17989) collected by the black plate technique, THAILAND, Nan province, Ban Huai Muang village, 19.1392019°N, 100.7199339°E, 25 December 2021, coll. Rawadee Kumlert; three larvae (ZIN 17990 – 17992) collected by the black plate technique, same place, 19.1386161°N, 100.7162079°E, 26 December 2021, coll. Kamonchanok Bunmee.

Three larvae (UoL) ex Gallus gallus domesticus, THAILAND, Nan province, Ban Huai Muang village, 19.139696°N, 100.720205°E, 24 December 2021, coll. S. Koosakulnirand.

Genus Leptotrombidium Nagayo, Miyagawa, Mitamura & Imamura, 1916

Leptotrombidium deliense (Walch, 1922)

Distribution and hosts — Australia, Cambodia, China, India, Indonesia, Laos, Malaysia, Maldive Islands, Myanmar, Nepal, Papua New Guinea, Philippines, Sri Lanka, Taiwan, Thailand, Vietnam, ex a wide range of mammal hosts (including humans), birds, occasionally on reptiles and arthropods (Stekolnikov 2021a).

Material examined — One larva (ZIN 17936) ex Pellorneum ruficeps, MALAYSIA, Pahang State, Fraser's Hill, 3.725630°N, 101.716365°E, 22 October 2021, coll. P. Rajasegaran; one larva (ZIN 18171) ex P. ruficeps, MALAYSIA, Kedah State, Langkawi Isl., Gunung Machinchang, 6.429010°N, 99.729852°E, 16 March 2022, coll. P. Rajasegaran.

Leptotrombidium imphalum Vercammen-Grandjean & Langston, 1976

Distribution and hosts — Sri Lanka, China, India, Malaysia, Myanmar, Pakistan, Taiwan, Thailand, ex 19 species of mammals from four orders and ex one unidentified bird (Stekolnikov 2021a). Amaurornis phoenicurus and Lewinia striata are new host species.

Material examined — Two larvae (ZIN 17933, 17934) ex Amaurornis phoenicurus and Lewinia striata, MALAYSIA, Sarawak State, Sematan Pueh village, 1.831126°N, 109.708966°E, 22 March 2022, coll. P. Rajasegaran.

Leptotrombidium miculum (Traub & Audy, 1954)

Distribution and hosts — Malaysia, Thailand, ex five species of rodents (Stekolnikov 2021a). Here this species is for the first time recorded on a bird host.

Material examined — One larva (ZIN 17932) ex Pellorneum ruficeps, MALAYSIA, Kedah State, Langkawi Isl., Gunung Machinchang, 6.429010°N, 99.729852°E, 17 March 2022, coll. P. Rajasegaran.

Genus Odontacarus Ewing, 1929

Odontacarus audyi (Radford, 1946)

Distribution and hosts — India, Malaysia, Thailand, Vietnam, on 22 bird species (Stekolnikov 2021a). Cacomantis sepulcralis, Cyornis tickelliae, Eumyias thalassinus, Geokichla citrina, Geokichla sibirica, Larvivora cyane, Philentoma pyrhoptera, Cyornis brunneatus, Stachyris nigriceps, and Stachyris poliocephala are new host species.

Material examined — Three larvae (ZIN 17938 – 17940) ex Geokichla citrina, Geokichla sibirica, and Larvivora cyane, THAILAND, Rayong province, Koh Mun Nai, 12.612384°N, 101.687574°E, 10 – 11 March 2021, coll. S. Koosakulnirand; two larvae (ZIN 17941, 17943) ex L. cyane and Cyornis tickelliae, THAILAND, Kanchanaburi province, Mahidol University Campus, 14.1288777°N, 99.1611407°E, 8 – 9 December 2021, coll. S. Koosakulnirand; one larva (ZIN 17942) ex L. cyane, THAILAND, Kanchanaburi province, SW Mahidol University Campus, 14.11806°N, 99.15253°E, 9 December 2021, coll. S. Koosakulnirand; two larvae (ZIN 17944, 17945) ex L. cyane and Copsychus malabaricus, THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.13111°N, 99.14863°E, 10 December 2021, coll. S. Koosakulnirand; one larva (ZIN 18167) ex Gallus gallus domesticus, THAILAND, Nan province, Ban Santisuk village, 19.131006°N, 100.698332°E, 23 December 2021, coll. S. Koosakulnirand.

Fifty-three larvae (UoL) from the same localities of Kanchanaburi province, same and additional host individuals of the same species, plus 11 larvae ex one Copsychus saularus (2), one Mixornis gularis (1), two Pycnonotus conradi (4), and two Rhipidura javanica (4), THAILAND, Kanchanaburi province, Mahidol University Campus, 14.1288777°N, 99.1611407°E, 9 December 2021, coll. S. Koosakulnirand; nine larvae (UoL) ex one Mixornis gularis (2), two Pycnonotus conradi (4), and one Rubigula flaviventris (3), THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.13111°N, 99.14863°E, 10 December 2021, coll. S. Koosakulnirand; 53 larvae (UoL) ex three Copsychus malabaricus (7), four Cyornis tickelliae (15), four Larvivora cyane (15), one Pycnonotus aurigaster (2), four Pycnonotus conradi (8), and two Pycnonotus finlaysoni (6), THAILAND, Kanchanaburi province, W Mahidol University Campus, 14.134225°N, 99.1374365°E, 11 December 2021, coll. S. Koosakulnirand; nine larvae (UoL) ex one Dicrurus paradiseus (1), one Larvivora cyane (3), one Calliope calliope (3), one Ficedula albicula (1), and one Pycnonotus conradi (1), THAILAND, Kanchanaburi province, NW Mahidol University Campus, 14.154772°N, 99.1193296°E, 12 – 13 December 2021, coll. S. Koosakulnirand.

Three larvae (UM) ex Pellorneum ruficeps, Geokichla citrina, and Larvivora cyane, MALAYSIA, Kedah State, Langkawi Isl., Gunung Machinchang, 6.429010°N, 99.729852°E, 16 – 17 March 2022, coll. P. Rajasegaran; one larva (UM) ex P. ruficeps, MALAYSIA, Pahang State, Fraser's Hill, 3.725630°N, 101.716365°E, 22 October 2021, coll. P. Rajasegaran; five larvae (UM) ex Cacomantis sepulcralis, Copsychus malabaricus, Eumyias thalassinus, Stachyris nigriceps, and Stachyris poliocephala, MALAYSIA, Selangor State, Ulu Gombak Forest Reserve, 3.325987°N, 101.752747°E, 9 – 12 February 2021, coll. P. Rajasegaran; 16 larvae (UM) ex one C. malabaricus (1), four L. cyane (5), four Philentoma pyrhoptera (4), one Cyornis brunneatus (2), and four S. poliocephala (4), MALAYSIA, Terengganu State, Pasir Raja Forest Reserve, 4.790517°N, 102.996835°E, 23 – 27 October 2021, coll. P. Rajasegaran.

Genus Parascoschoengastia Vercammen-Grandjean, 1960

Parascoschoengastia heynemani (Nadchatram & Upham, 1966)

Distribution and hosts — China and Malaysia, ex Halcyon pileata (Boddaert), Alcedo atthis bengalensis J.F. Gmelin, Alcedo peninsulae, and Alcedo meninting Horsfield (Coraciiformes: Alcedinidae) (Stekolnikov 2021a). Actenoides concretus is a new host species.

Material examined — Four larvae (UM) ex one Actenoides concretus, MALAYSIA, Pahang State, Krau Wildlife Reserve, 3.596982°N, 102.183190°E, 18 February 2021, coll. P. Rajasegaran; four larvae (UM) ex one Alcedo peninsulae, MALAYSIA, Sarawak State, Gunung Gading National Park, Lundu, 1.692098°N, 109.845157°E, 22 March 2022, coll. P. Rajasegaran.

Characteristics of infestation

Thailand. In total, 754 hosts were examined; 199 (26.4%) were found parasitized by chiggers (2,340 specimens); 440 chigger specimens from 140 hosts were slide-mounted and identified (Table 1). There were 30 hosts (22%) bearing more than one chigger species, considering only those cases confirmed by the identification of slide-mounted chiggers. One individual of Geokichla citrina from Koh Mun Nai was parasitized by three species (N. solitus, O. audyi, and T. densipiliata). The pairs of co-occurring species were N. longipes and O. audyi (19 cases), N. longipes and T. kirhocephales (3), N. (W.) andamanensis and S. archaea (3), O. audyi and T. kirhocephales (2), O. audyi and T. densipiliata (1), and E. wichmanni and H. comata (1).

Malaysia. In total 777 hosts were examined; 129 (16.6%) were found parasitized by chiggers; 242 chigger specimens from 123 hosts were slide-mounted and identified (Table 2). One Pellorneum ruficeps from Fraser's Hill bore three species (E. cosmetopode, L. deliense, and O. audyi); whereas four hosts bore pairs of species—O. audyi and T. densipiliata (2), L. miculum and O. audyi (1), and L. imphalum and B. acuscutellaris (1).

Discussion

The specificity of chigger mites for different orders of birds is a trait that can be noted first of all when considering our results. Thus, our materials from Thailand demonstrate three different sets of chigger species connected with birds from different orders occurring in different habitats (Table 9). Shorebirds (order Charadriiformes) were parasitized by four species of Neacariscus and by Schoengastia archaea. Birds inhabiting forests (mainly Passeriformes) bore two species of Neoschoengastia (N. longipes and N. solitus), two Toritrombicula spp., and Odontacarus audyi. Domestic chickens (Galliformes) were parasitized by Eutrombicula wichmanni, Neoschoengastia gallinarum, Helenicula comata, and O. audyi. Thus, only the latter species was found on birds belonging to two of these ecological (and taxonomic) groups.

In the materials from Malaysia (Table 10), we can see that Galliformes, represented in this collection by four species of pheasants in addition to domestic chickens (Table 2), were the hosts of a sole chigger species, Neoschoengastia gallinarum. The chigger species composition on Passeriformes was similar to that of Thailand and included two species of Toritrombicula and O. audyi. Other recorded species were rare. Finally, Parascoschoengastia heynemani was found only on two species of kingfisher (Coraciiformes: Alcedinidae), in two localities from different provinces. Noteworthy is that previous records of this species were on hosts from the same family (Stekolnikov 2021a).

Since chigger mites are temporary parasites, their distribution is expected to be determined by the natural conditions of the biotopes suitable both for their free-living postlarval stages and for their hosts. However, the size of actually recorded host ranges for different chigger species can be highly variable and dependent, theoretically, on the number of host species in some localities and the modes of chigger activity; for example, preferred habitats where they lie in wait for their hosts (ground surface, grass, tree branches, etc.). These aspects of their behavior are poorly known: however, the connection of P. heynemani with kingfishers suggests this chigger species is nidicolous, occupying the burrows in which kingfishers nest. Similarly, A. lorius larvae and post-larval stages were found together in tree-hollow nests of psittaciform birds in Queensland, Australia, indicating that the entire lifecycle of this species can be nidicolous (Shaw 2010). Such ecological habits could explain the infestation of the buff-necked woodpecker (M. tukki) by A. lorius in Malaysia, as this host species also nests in tree hollows.

The separate set of chigger species from the shorebirds in Thailand was the most unexpected discovery during our investigation. Among the five chigger species collected from the birds inhabiting the seashore of southern Thailand, Schoengastia archaea and Neacariscus sulae were previously known only from their type localities in West Africa. Neacariscus pluvius was previously recorded only in Oceania, and N. shiraii from Oceania and Japan. One species of this genus was described above as new.

According to the literature, species of the genus Neacariscus parasitize mainly aquatic birds (Vercammen-Grandjean and Langston 1976; Mertins et al. 2009). One species, N. thompsoni, in addition to the birds, was found on a fish-eating bat. Only two species, N. chaetosa and N. nativitatis, are known from lizards in Central and South America; while N. shiraii was occasionally collected on rats. However, where the collection sites of these species are known, they tend to be located in coastal areas accessible to seabirds (Mertins et al. 2009; Stekolnikov and González-Acuña 2015). Schoengastia archaea was also described from a species of Charadriiformes. We assume that the fauna of chiggers inhabiting seashores and parasitizing the birds associated with these biotopes is mostly uniform throughout the tropical zone of the world. Probably, Schoengastia galapa, described from the Galápagos Islands belongs to the same species complex, although it was collected only from a marine iguana (Stekolnikov 2021b). Its presence on seabirds seems probable.

Migration of birds could facilitate widespread dispersal of the bird chiggers, such as S. archaea and N. sulae. Varma (1964) discussed this possibility in detail. In part, the wide range of Blankaartia acuscutellaris, which extends from Southeast Asia to Western Europe and Africa, could be connected with the fact that principal hosts of this species are birds associated with wetlands (although it has been frequently collected from other hosts, including humans) (Mąkol and Korniluk 2017; Trnka et al. 2022). Recently, a disjunctive area of distribution, consisting of three isolated parts—Eastern Europe, Iran, and Vietnam—was established for Neotrombicula elegans (Shamsi et al. 2020). Since in Vietnam this species was found on three species of birds, including Larvivora sibilans (Swinhoe), which was noted as a rare vagrant in Europe (Clement and Rose 2015), these authors hypothesized that dissemination by birds could be the cause of the scattered range of N. elegans.

We add that alternative migration routes within the same population of birds can result in the presence of greatly disjunct wintering sites, both latitudinally and longitudinally. Thus, the wintering sites of the little ringed plovers Charadrius dubius Scopoli (Charadriiformes: Charadriidae) breeding in south Sweden were identified as far apart as West Africa and India using geolocators (Hedenström et al. 2013). Similarly, Terek sandpiper (X. cinereus), which we found to be parasitized with three Neacariscus spp. and S. archaea in Thailand, has a vast breeding range across the taiga from Finland to eastern Siberia. Its wintering grounds extend from eastern and southern Africa, the Middle East, southern Asia, and Australia, with vagrants appearing as far afield as the Americas (White et al. 2006). Provided that the breeding sites of some bird species are suitable to support the life cycle of chiggers (at least for part of the year), variability of migration routes could thus result in extensive meridional dissemination of chiggers over vast distances.

The chigger species composition on the Passeriformes in the study areas significantly differed from that of the seven passerine bird species examined by Kaluz et al. (2016) in North Vietnam. Among the 12 chigger species found by these authors, only one (O. audyi) was also recorded in our study. Moreover, they found no species of Toritrombicula, whereas we recorded three, and this genus was rather frequent in our collections (Tables 9, 10). In Thailand, we collected two species of Neoschoengastia from passerines whereas three other species from the same genus were reported by Kaluz et al. (2016). In contrast, we did not find this genus on Passeriformes in the Malaysian localities. Finally, we collected three species of Leptotrombidium from Passeriformes in Malaysia, but none in Thailand, while Kaluz et al. (2016) found six other Leptotrombidium species. Evidently, the fauna of bird chiggers in forest biotopes of Southeast Asia is highly variable and requires further investigations, including quantitative analysis of host-chigger networks using the data presented here, which will be the subject of a separate publication.

Acknowledgements

We thank Dr Nikita Chernetsov (Zoological Institute, Saint Petersburg, Russia) for useful information on bird migrations, and Dr Somying Thunhikorn and Dr Kirana Noradechanon of the DNP for facilitating access to national parks in Thailand. Elsewhere in Thailand we also acknowledge the assistance of Mr Jirut Khamaye and the field research team during sampling in the Bueng Boraphet Non-Hunting Area and Mr Suthep Jualaong, Director, Eastern Marine and Coastal Resources Center (EMCOR), Department of Marine and Coastal Resources, on Koh Mun Nai. In Malaysia, we were very grateful for the support of the field team from the DWNP (Ismail Hj. Mamat, Abdul Rahman bin Ahmad, Mohd Hairol Mat Zin, Adzri bin Azmi, Stewart Angin, and Suhaimi bin Mansor); research assistants Nuramirah Diyanah binti Mohd Johan and Siti Nurul Izzah binti Mohd Azami from Universiti Malaya; and Dr Mohammad Saiful bin Mansor's field team from Universiti Kebangsaan Malaysia. This research was supported by a Royal Society International Collaboration Award (ICA\R1\191058) awarded to BLM and SA; a Mahidol-Liverpool PhD scholarship awarded to SK; the Higher Institution Centre of Excellence (HICoE), Universiti Malaya; and the Ministry of Science and Higher Education of the Russian Federation (122031100263-1, to AAS).

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