Smelling, Searching, and Sabotage: Effects of Two Primary Colonizers, Lucilia sericata (Meigen) (Diptera: calliphoridae) and Nicrophorus vespillodies (Herbst) (Coleoptera: silphidae), on Carrion Volatiles and Attraction

Abstract

Carrion is an ephemeral, high value, patchy resource that inspires intense competition. This leads to selective pressures on the processes that govern its location and use (e.g., foraging behaviors, reproductive strategies). Resource location, evaluation, and acceptance are complex behaviors influenced by numerous factors including existing colonization, sex, and physiological state of the forager. Foragers use public information in their environment to make ecologically relevant decisions regarding resources and oviposition. Volatile organic compounds (VOCs) comprise a significant portion of this information suite, and their microbial origin makes microbes not only a competitor but an integral part of the public information system by which resource evaluation occurs. For primary colonizers, evaluation takes place during the pre-colonization interval (pre-CI), which has been relatively understudied. To further decipher the mechanisms governing the pre-CI, volatile profiles of small carrion at varying lengths of decomposition (24 h and 72 h) and states of colonization (uncolonized, colonized by Lucilia sericata or Nicrophorus vespilloides) were generated to determine how VOCs (i.e., public information) change with resource use. Treatments generated distinct volatile profiles, most notably demonstrating exclusion of indole (high quality, fresh resource indicator) from all beetle-colonized treatments and inclusion of dimethyl disulfide (indicative of later decomposition) in fresh beetle-colonized treatments. The foraging preferences of L. sericata were tested to assess how resource age and colonization affect olfactory and oviposition preferences. Flies displayed a strong olfactory preference for aged resources with no effect of existing colonization, with 80-90% choosing aged treatments. Preference was confirmed in the oviposition assay, with between 77-100% of eggs laid on aged uncolonized treatments; however, there was an effect of existing colonization, with < 5% of eggs being laid on any aged fly-colonized treatment. Results indicate that insect interaction changes VOC profiles, with beetles potentially manipulating public information via microbial regulation to deter competitors. Results also suggest a shift in L. sericata preference on small resources from “primary colonizer” to delayed colonization in a possible effort to avoid competition. Data provide important foundations upon which to explore competitive interactions of carrion users, manipulation of public information in the carrion system, and the mechanisms governing the pre-colonization interval.