Intraspecific Variations of Idiosomal Setal Patterns of Phytoseiid Mites

Abstract

Intraspecific variation of idiosomal setal patterns was examined in field populations of eight phytoseiid species and in laboratory populations of Neoseiulus californicus and N. womersleyi. In field populations, about 6.4-16.1% of females showed setal variation, whereas in laboratory populations, this percentage was relatively low in N. californicus (5.8-14.8%) but high in N. womersleyi (8.6-36.1%). Setal variations were divided into the following categories: absent, additional, inserted, deviated, expanded, and shortened setae. An absence of setae was more common than additional or inserted setae, both in the field and laboratory populations. Expanded and shortened setae were rare. An absence of setae was frequently observed on the ventral opisthosoma, and occurred on both of its sides (left and right), mainly at ZV3 in N. womerwelyi and JV3 in Typhlodromus vulgaris. In the IG population of N. womersleyi, an absence of setae was frequently observed at ZV1 (49.5% of the total absent setae in the population) and ZV3 (37.8%), which was significantly different from the other populations. The difference in setal variation between field and laboratory populations suggests that it is not caused by accidental defects during post-embryonic development but rather is the result of heritable traits. The maintenance of the absence of setae in field populations may create a driving force from holotrichous to hypotrichous conditions, and may produce higher levels of species diversity in phytoseiid mites.