Life table of the red spider mite Tetranychus bastosi (Acari: Tetranychidae) on different host plants

Tetranychus bastosi Tuttle, Baker & Sales was described from Ceará state, northeastern Brazil. It has so far been reported from 25 plant species, among which cassava (Manihot esculenta Crants), common bean (Phaseolus vulgaris L.) and papaya (Carica papaya L). Although there is no information about its impact on crop yield, high population levels have been observed on some crops, leading to suppose that damage might occur in some occasions. In this study, fertility life table parameters were calculated for T. bastosi on cassava, common bean and papaya at 25 ± 2 °C, 70 ± 5% RH and photoperiod of 12/12 h. The best performance of T. bastosi occurred on C. papaya and P. vulgaris, on which the intrinsic rate of population increase reached 0.184 and 0.183 female/female/day, respectively. These results agree with the most common occurrence of this mite on papaya and on common bean than on cassava.


INTRODUCTION
Tetranychus bastosi Tuttle, Baker & Sales was originally described from specimens collected on red mulberry, Morus rubra L. (Moraceae), in Crato, Ceará state, Brazil (Tuttle et al 1977). It now seems to be widespread in that country, where it has been reported from the northern, northeastern and southeastern regions; it still has not been reported from other countries (Migeon & Dorkeld 2006). Tetranychus bastosi has been found on 25 plant species (Bastos et al 1979, Moraes & Flechtmann 1980, 1981, Bolland et al 1998, Santos et al 2010, Mendonça et al 2011, Sarmento et al 2011, Cruz et al 2012, Lofego et al 2013, Rosado et al 2014. It has been mentioned as a potential pest of some crops (Moraes & Flechtmann 2008, Santos et al 2010. Among the plants cultivated in northeastern Brazil, T. bastosi seems to reach particularly higher levels on bean (Phaseolus vulgaris L.) plants. The biology of this mite was studied on Jatropha curcas L. (Euphorbiaceae) (Pedro Neto et al 2013), which has been considered for cultivation in several tropical countries for biodiesel production (Openshaw, 2000).
Thus, the objective of this paper was to compare the biotic potential of T. bastosi on bean plants and two other plant species onto which it has been found, namely cassava (Manihot esculenta Crantz) and papaya (Carica papaya L.), all important crops in Brazil. Our hypothesis was that T. bastosi has a better biological performance on bean than on those other plant species. Although there is no official information on the economic importance of this mite species, it has become increasingly common in northeastern Brazil and information about their biology are necessary for their management.

MATERIALS AND METHODS
Approximately 300 specimens of T. bastosi were collected from Turnera subulata Sm. (Turneraceae), in Crato (7°05'S -39°40'W and 461 m altitude), Ceará state. These were used to establish stock colonies on cassava, common bean and papaya plantlets. The colonies were maintained separately for at least three months before the beginning of the evaluations, in a greenhouse, at ambient conditions. Tests were conducted at 25 ± 2°C, 70 ± 5% RH and photoperiod of 12/12 h.
To obtain the eggs to start the evaluations, a group of 50 females was transferred from each stock colony to separate experimental units consisting of a piece (4 x 4 cm) of a leaf of the respective plant species onto which they had been held, placed with the abaxial surface up onto a disk of polyethylene foam mat in a Petri dish. The edges of the leaf piece were covered by a strip of cotton wool that contacted the polyurethane mat, which was maintained wet by daily addition of distilled water.
Eight hours later, the females were removed and the eggs laid were observed every 8 h to determine survivorship and duration of embryonic development. After hatching, each larva was isolated in an experimental unit similar to that described in the previous paragraph. Post-embryonic immatures were also observed every 8 h to determine survivorship and duration of each stage. After adult emergence, males were kept in isolation, whereas one male from the stock colony was transferred to each unit containing a recently molted female. When dead, males were replaced by new males from the same source. Oviposition level was determined by daily examination of each unit. The experimental units were replaced periodically (every third to fourth day) to ensure adequate physiological conditions of leaf piece. The progeny of each female was reared separately to adulthood to determine sex ratio.
Data analysis was done within a completely randomized design, with three treatments, each corresponding to a plant species, and each replicate corresponding to one mite. The test was initiated with 142 eggs when the substrate was P. vulgaris and 125 eggs on each of the other substrates. Data were tested for normality and homogeneity of variance and subsequently subjected to variance analysis and compared by Tukey's HSD test (5% significance level), using the software GraphPad Prism 5 version.
Fertility life tables were prepared according to Birch (1948). Biological parameters and estimates for their variances were calculated by "LifeTable SAS" (SAS Institute 1999-2001, adapted by Maia et al (2000). Biotic parameters were compared by Stu-dent´s t tests.

RESULTS
For females and males, durations of each stage and of the whole immature phase were generally similar on the different host plants, although significant differences were observed for some developmental stages and in those cases the longest durations were observed on M. esculenta (F (0.823) = 772, P < 0.0001) ( Table 1).
Development from egg to adult female ranged from 10.5 days on P. vulgaris to 12.3 days on M. esculenta, whereas development from egg to adult male ranged from 10.3 days on P. vulgaris to 13.4 days on M. esculenta. Consequently, a similar pattern was observed when females and males were considered together, with durations from egg to adult ranging from 10.5 days on P. vulgaris to 12.5 days on M. esculenta.
No significant differences were observed for the durations of pre-oviposition and oviposition periods on the different host plants, but the duration of the post-oviposition period was significantly shorter on P. vulgaris (F (2,118) = 5.37, P < 0.0059) and longevity was longer on C. papaya (F (2,98) = 1.54, P < 0.219) ( Table 2).
These parameters were almost twice as high on C. papaya as on M. esculenta, and intermediate in P. vulgaris. Sex ratio (proportion of females) was high on the three host plants in both parental and F1 generations, ranging between 0.80 and 0.89.  (Table 4) showed best performance of T. bastosi on C. papaya and P. vulgaris, which was compatible with the significant slower immature development and lower reproduction rates on M. esculenta. Means (Confidence Interval-95%) followed by the same letter in the same line, do not differ by comparisons of treatments two by two with confidence interval at 95% probability after estimating errors by the Jackknife method.

DISCUSSION
The results indicated that papaya and common bean were the best hosts for T. bastosi, allowing quicker development of the immature stages and higher oviposition rates. These partially confirmed our hypothesis. Biotic parameters determined on those hosts were lower than determined by Pedro Neto et al (2013) for the same mite species on J. curcas, but their study was conducted at slightly higher temperature (26°C). Yet, the population growth was higher than determined for another world important tetranychid pest, the two spotted spider mite, Tetranychus urticae Koch, on several plant species ( Tetranychus urticae is an important pest of papaya and common bean in Brazil. However, in the drier areas of northeastern Brazil, T. bastosi occurs more frequently on irrigated C. papaya than T. urticae and may cause significant damage to this crop (Moraes & Flechtmann 1980;Moraes & Flechtmann 2008).
In the urban area of Piracicaba, São Paulo state, in southeastern Brazil, T. bastosi has been found in large populations on Amaranthus sp. and Turnera sp. during the dry season, leaving other neighboring plant species untouched. Quite often, the phytoseiid mite Neoseiulus idaeus Denmark & Muma is found on those plants preying upon the different stages of T. bastosi, as reported by Moraes & McMurtry (1983) in northeastern Brazil. Preliminary trials conducted in greenhouses have shown that when infested leaves are transfered from those plants onto common bean plants, the mite attain high population levels. Tetranychus bastosi may actually be more widespread than presently known, given its great morphological similarity with other red species of tetranychid mites, from which they can be separated by the shape of the male aedeagus (Tuttle et al 1977).