ABSTRACT Background: Local mate competition theory predicts a female-biased sex ratio if one or a few hymenopteran foundresses, such as parasitoid wasps, oviposit in a local patch, and a less female-biased sex ratio as the number of foundresses increases. Although hemipterans, whiteflies are also haplodiploid insects, and the spatial structure of whitefly populations is similar to that of wasps. Question: Do whitefly sex ratios match the theoretical predictions of local mate competition? Organism: The spiralling whitefly, Aleurodicus dispersus Russell (Hemiptera: Aleyrodidae), a newly invasive, destructive pest on Hainan Island, China. Methods: We investigated the effects of the number of foundresses on the sex ratio of A. dispersus. Results: Offspring sex ratio was female-biased when only one foundress oviposited in a patch. Sex ratio increased with the number of foundresses. When only one foundress laid eggs in a patch, offspring sex ratio declined as the number of offspring increased. Male offspring emerged earlier than female offspring. Conclusion: Local mate competition predicted the trends in sex ratio of the spiralling whitefly
