Interkingdom Signaling by Bacteria Associated with Conspecific and Heterospecific Eggs of Cochliomyia macellaria and Chrysomya rufifacies (Diptera: Calliphoridae) Governs Secondary Colonization of Carrion. crufcmac_eggs

Blow flies (Diptera: Calliphoridae) are a primary mechanism for recycling vertebrate carrion. In most instances, initial colonization by blow flies results in heightened attraction and colonization by conspecific and heterospecifics. We examined the response of Cochliomyia macellaria (native to North America) and Chrysomya rufifacies (invasive) to conspecific and heterospecific eggs. Because C. rufifacies is predaceous on conspecific and heterospecific larvae, we hypothesized that there would be selection for adults to detect and respond (attraction and/or repellence) to the presence of conspecific and heterospecific eggs on a resource whose occurrence is difficult to predict and short-lived. Using a Y-tube olfactometer, we measured the residence time response of C. macellaria and C. rufifacies to conspecific and heterospecific eggs of three different age classes ranging from fresh to 9-h-old (close to hatch). We then examined the response of these flies to eggs that were surface sterilized and to egg wash which was thought to contain many of the egg-associated microbes. High throughput sequencing was used to characterize the bacterial fauna associated with different ages of eggs from these two species. A general analysis revealed that C. macellaria was significantly repelled by C. rufifacies eggs. Chrysomya rufifacies did not show a preference to either species of eggs, although C. macellaria egg-associated bacteria did release volatiles that attract adult flies. Sex class provided limited insight to the behaviour of adult blow flies. Gravid females of both species provided more consistent responses to eggs than either non-gravid or males. Surface sterilization of eggs attracted C. macellaria gravid females significantly more to conspecific eggs of greater age, while their response to heterospecific eggs was to be significantly repelled. C. rufifacies gravid females, on the other hand, were in direct contrast to C. macellaria but also exhibited a significant attraction to heterospecific eggs regardless of their age. These behaviors are most likely tied into the predator-prey interactions between the two species. High throughput analysis revealed C. rufifacies has a similar egg-associated fauna as C. macellaria, which may serve as a form of camouflage allowing it to colonize and thereby attract C. macellaria which is a common prey for its larvae.