A window into fly sex: mating increases female but reduces male longevity in black soldier flies

Sexual reproduction increases genetic diversity but it is also associated with costs such as exposure to parasites or reduced life span. Black soldier flies, Hermetia illucens, are a suitable model to investigate the trade-offs between reproduction and longevity as they largely rely on their larval resources and do not have to feed as adults. Here, we investigated the influence of mating status on adult longevity. We found that females had shorter longevity than males, but the intersexual difference in life span was reduced through mating which increased female but decreased male longevity. This suggests a cost of mating for males, while female longevity increased, likely via nutrients transferred by males during copulation (sensu nuptial gifts). We also investigated the transparent abdominal 'window' of adult black soldier flies, the fullness of which may be a proxy for both age and mating status. Window fullness decreased with age in unmated males whereas unmated females maintained high fullness until they were older. Additionally, mated females mostly had full windows while those of mated males were mostly empty. Our findings have not only expanded our understanding of resource allocation in this species, but they also harbour great potential for applicability in the industrial sector given the extensive use of black soldier flies in organic waste management.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Automated summary

Sexual reproduction increases genetic diversity but also has associated costs such as exposure to parasites and reduced life span. In this study, we investigated the impact of mating status on the longevity of adult black soldier flies. We found that females had shorter longevity than males, but mating increased female longevity while decreasing male longevity. Additionally, we examined the abdominal 'window' of the flies and found that window fullness decreased with age in unmated males, while unmated females maintained high fullness until older ages. Mated females mostly had full windows, while mated males had mostly empty windows.