Sex ratios in the haplodiploid herbivores, Aleyrodidae and Thysanoptera: A review and tools for study

Sex allocation studies in hymenopterans have been used to test adaptive predictions, to predict the quality of biological control agents, to theorize how eusociality is maintained, and to predict population dynamics. Almost all hymenopterans are haplodiploid, so mothers may have an ability to adaptively adjust sex allocation. The insect order Thysanoptera (thrips) and the Hemipteran family Aleyrodidae (whiteflies) are also haplodiploid and include important agricultural pests, but have been the subject of comparatively few sex allocation studies. This review summarizes studies of Aleyrodidae and Thysanoptera sex ratios as influenced by temperature, host plant, nutrition, conspecifics, competitors, endosymbionts, predators, parasitoids and other pathogens. Sex ratio influences were reported in studies testing effects of temperature, host plant, conspecifics, competitors, bacterial endosymbionts and a fungal pathogen. Viruses, predators, and parasitoids were not found to affect sex ratios in Aleyrodidae and Thysanoptera, although not many studies have collected the data to assess these factors. Because sex ratio studies in Thysanoptera and Aleyrodidae have only recorded secondary, adult or operational sex ratios instead of primary sex ratios at oviposition, differential developmental mortality is a potential confounding variable for interpreting all of these records, and it is difficult to confirm whether sex ratios reflect sex allocation. To conclude whether sex allocation by mothers is taking place, primary sex ratios need to be recorded. Our review refers to a cytogenetic and survival assay to find primary sex ratios or confirm differential developmental mortality in these haplodiploid organisms.