Host plant quality mediates dispersal, oviposition, and sex allocation in a Tetranychus spider mite.

Dispersal is a key adaptive strategy to escape deteriorating environments, and habitat selection by dispersers is critical to their own and offspring fitness. Using the haplodiploid spider mite Tetranychus ludeni Zacher as a model species, we investigated how host plant quality influenced dispersal probability, habitat selection, and subsequent reproductive performances. We tested two dispersal scenarios: mated females had triple choice, i.e. residing in low-quality (LQ) or high-quality (HQ) habitat or dispersing to a LQ or HQ habitat. Results show that significantly more females dispersed from LQ habitats than from HQ habitats, and dispersers preferred to settle in HQ habitats regardless of the dispersal scenarios. However, aggregating in HQ habitats resulted in a higher number of eggs accumulated but increased immature mortality which induced restraint of the per capita fecundity. Females dispersed from LQ habitats produced significantly smaller eggs but maintained a similar proportion of daughters compared to those remaining in LQ habitats, whilst females dispersed from HQ habitats produced eggs of a similar size but a significantly higher proportion of daughters, suggesting that dispersing females might manipulate offspring sex ratio by lowering the fertilisation threshold to fertilise relatively smaller eggs. Increasing female density strongly restrained the per capita fecundity when dispersed from LQ to LQ habitats, but increased egg size and daughter production when residing in HQ habitats. Egg size had no significant effect on egg hatching or immature survival. This study delivers insights into the dispersal and reproductive strategies of a haplodiploid species, highlighting how host quality shapes adaptive responses in challenging environments.