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Highly competitive ephemeral resources like carrion tend to support much greater diversity relative to longer-lived resources. The coexistence of diverse communities on short-lived carrion is a delicate balance, maintained by several processes including competition. Despite this balance, few studies have investigated the effect of competition on carrion, limiting our understanding of how competition drives coexistence. We investigated how priority effects and larval density influence coexistence between two blowfly species, the facultative predator Chrysomya rufifacies and its competitor Calliphora stygia, which occupy broadly similar niches but differ in their ecological strategies for exploiting carrion. We examined how adult oviposition, larval survival, developmental duration, and adult fitness were affected by the presence of differently aged heterospecific larval masses, and how these measures varied under three larval densities. We found C. rufifacies larval survival was lowest in conspecific masses with low larval densities. In heterospecific masses, survival increased, particularly at high larval density, with priority effects having minimal effect, suggesting a dependency on collective exodigestion. For C. stygia, we found survival to be constant across larval densities in a conspecific mass. In heterospecific masses, survival decreased drastically when C. rufifacies arrived first, regardless of larval density, suggesting C. stygia is temporally constrained to avoid competition with C. rufifacies. Neither species appeared to completely outcompete the other, as they were either constrained by density requirements (C. rufifacies) or priority effects (C. stygia). Our results provide new mechanistic insights into the ecological processes allowing for coexistence on a competitively intense, ephemeral resource such as carrion., (© 2022. The Author(s).)

Cuticular hydrocarbons (CHCs) play an important role as contact pheromones in insects, particularly in flies. However, for many fly taxa our understanding of the importance of CHCs in sexual communication is limited. Within the family Calliphoridae (blowflies), sex-specific differences in CHCs have been reported for several species, but there is no evidence that CHCs facilitate sexual behavior. In order to elucidate the function of CHCs in Calliphoridae, studies combining behavioral and chemical analyses are required. The present study used gas chromatography/mass spectrometry, along with behavioral assays, to assess whether CHCs facilitate sexual attraction in the small hairy maggot blowfly, Chrysomya varipes. The specific aims were to: 1) determine if CHCs differ between the sexes and 2) assess whether flies exhibit positive chemotaxis to CHCs of the opposite sex. Fifty-two hydrocarbons common to both sexes were identified, and quantitative differences for numerous CHCs were observed between the sexes. However, behavioral assays provided no evidence that flies were attracted to CHCs of the opposite sex, challenging the hypothesis that CHCs facilitate sexual attraction in Ch. varipes. In contrast to other blowflies, Ch. varipes males invest heavily in courtship displays and ornamentation, so we speculate that visual communication in this species may have relaxed sexual selection for chemical communication. More broadly, our findings support suggestions that CHCs may not always facilitate insect sexual communication.