Slight morphological differences and reproductive isolation between some populations of Euseius indicated the existence of a complex of 3 species on avocado trees from southern California, USA, south through Mexico and Central America: E. hibisci in California and inland areas of Mexico south to Oaxaca; E. vivax in the warmer, humid areas of southern Mexico and in Central America; and E. quetzali n. sp. from the mountain areas of Guatemala and Chiapas, Mexico. Partial reproductive incompatibility (P, progeny all or mostly males) was observed between northern and southern populations of E. hibisci in Mexico al1d between California and Mexico populations.