Sex Ratios in Haplodiploid Herbivores (Aleyrodidae and Thysanoptera): A Review and Tools for Study

Abstract

Studies confirming adaptive sex allocation, or a flexible relative investment in males and females, have been extensive in Hymenoptera, and have been used to predict the quality of biological control agents, to theorize how eusociality is maintained, and to predict population dynamics. Most hymenopterans are haplodiploid, in which females are derived from fertilized eggs and males from unfertilized eggs, so haplodiploid mothers may have a greater ability to adaptively adjust sex allocation. Thysanoptera and Aleyrodidae are also haplodiploid organisms, many of them being important agricultural pests, but less comprehensive studies on sex allocation have been performed with these taxa. Both taxa are also mostly herbivorous, drawing in new elements that may affect sex allocation patterns. This review is a summary of all studies of Aleyrodidae and Thysanoptera sex ratios as affected by temperature, host plant and nutrition, conspecifics, competitors, bacterial and viral endosymbionts, predators, parasitoids and other pathogens. Sex ratio influences were found 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 potential factors. Because sex ratio studies in Thysanoptera and Aleyrodidae have only recorded secondary, adult or operational sex ratios instead of primary sex ratios, differential developmental mortality is left as a confounding variable, and it is difficult to determine whether sex ratio changes are due to sex allocation. To conclude whether sex allocation of mothers is taking place, the primary sex ratios need to be recorded, so we have also included methods for tools, including cytogenetics and survival assays, to find primary sex ratios or confirm differential developmental mortality in these haplodiploid organisms. Future discoveries of sex allocation in Aleyrodidae and Thysanoptera may lead to better predictions of pest populations.