Female breeding-site preferences and larval feeding strategies of carrion-breeding Calliphoridae and Sarcophagidae (Diptera): a quantitative analysis

Protection from the elements, predators and parasitoids, and access to food is critical for insect larvae. Therefore, adult female insects are strongly selected to deposit offspring in safe, nutritious locations. Additionally, larvae may move to new feeding sites as food becomes depleted at the natal site. Maggots of carrion-breeding flies exploit patchy resources and are at risk from predators, desiccation and competition. Natural orifices, body folds, fur and feathers are protective locations that provide ready access to food, but their suitability as ovi- or larviposition sites may vary according to the degree of decomposition and presence of other larvae. Accordingly, female preference for ovi- or larviposition sites, and maggot distribution at feeding sites may depend upon carcass condition. We conducted a field experiment to investigate the preferences of female carrion flies for ovi- or larviposition sites on piglet carcasses. We also recorded movement of maggots on carcasses over the first 48 hours after carcass exposure. Females initially preferred to deposit offspring in the mouth; however, this preference changed to the body folds by 24 hours after the carcass exposure. Maggot distribution also changed over time, and the pattern suggested that individuals moved from food-depleted sites to more favourable locations.