The role of Wolbachia and the environment on sex determination of the Indian lac insect, Kerria lacca (Coccoidea: Tachardiidae)

Abstract

• In Kerria lacca , presence of endosymbiont Wolbachia is developmental-stage dependent. • Administration of antibiotic enhances the sex ratio of the lac insect multifold. • The lac insect sex ratio is influenced by environmental factors. • Mode of metamorphosis together with Wolbachia dynamics explains sex ratio changes. The Indian lac insect, Kerria lacca (Kerr) exhibits a highly variable sex ratio, apparently influenced by various environmental factors, in the absence of a chromosomal sex determination mechanism. The endosymbiont Wolbachia, well known as sex ratio distorter, was reported in this species but its role in the sex determination of the host has hitherto remained unexplored. Distinct variation in the presence of Wolbachia was observed in relation to the developmental stages and the sexes of K. lacca as well as the host plant species; adult males of W + whereas adult females are W -. The post-settlement environmental factors such as host plant, season and genetic makeup affect the sex ratio in this insect, probably mediated through Wolbachia dynamics. Denser settlement of the crawlers led to comparatively higher Wolbachia presence with an elevated sex ratio. Suppression of Wolbachia through antibiotic administration resulted in a nearly three-fold increase in the sex ratio. Distinct transitions in the proportion of insects with heterochromatic genome (cytological males) have been observed during the first instar on different host plants, indicating that changes in the sex ratio occur during early development phase. Environmental factors appear to influence Wolbachia , which in turn brings about sex ratio changes, probably mediated through changes in juvenile hormone levels, as the male and female lac insects show distinct modes of metamorphosis.