Pyrazine emission by a tropical firefly: An example of chemical aposematism?

Abstract

Although famous for photic courtship displays, fireflies (Coleoptera: Lampyridae) are also notable for emitting strong odors when molested. The identity of volatile emissions and their possible role, along with photic signals, as aposematic warnings of unpalatability have been little explored, especially in tropical species. Pursuant to the observation that the widespread Neotropical fireflies, Photuris trivittata and Bicellonycha amoena, emit pungent odors, glows, and flashes when handled, we investigated their cuticular and headspace chemistry. Gas chromatography-mass spectrometry analyses revealed that both fireflies have species-specific cuticular hydrocarbon profiles. Photuris trivittata headspace was dominated by 2-methoxy-3-(1-methylpropyl) pyrazine (hereafter, pyrazine), on the order of 1.59 ng/individual and a suite of sesquiterpenes, while B. amoena emitted 3-methoxy-2-butenoic acid methyl ester and a few ketones. This is the first report of such compounds in fireflies. We investigated the role of pyrazine in P. trivittata's interactions with potential predators: sympatric ants, toads, and bats. Solvent-washed P. trivittata painted with pyrazine incurred lower ant predation than did their solvent-washed counterparts. Pyrazine significantly repelled ants at baits in concentrations as low as 9.8 9 10 À4 ng/ll. The toad, Rhinella marina, readily accepted intact fireflies, pyrazine-coated and uncoated mealworms. Both Myotis nigricans and Molossus molossus bats rejected fireflies, but accepted both pyrazine-coated and uncoated mealworms. While pyrazine repels ants, its role as an aposematic signal warning other potential predators of firefly distastefulness requires further investigation. Our results underscore the idea that multiple enemies exert conflicting selection on firefly defenses. Abstract in Spanish is available with online material.

Species specificity and intraspecific variation in the chemical profiles of Heliconius butterflies across a large geographic range

“…We detected 2‐s‐butyl‐3‐methoxypyrazine in the genitals of H. melpomene , H. cydno , and H. timareta , and 2‐isobutyl‐3‐methoxypyrazine in the genitals of H. melpomene and H. cydno , both compounds known to deter predators in the wood tiger moth (Burdfield‐Steel, Pakkanen, Rojas, Galarza, & Mappes, 2018; Rojas et al, 2017, 2018; Rojas, Mappes, & Burdfield‐Steel, 2019). More generally, methoxypyrazines act as warning odors in other insects (e.g., Lepidoptera, Rothschild, Moore, & Brown, 1984; fireflies, Vencl et al, 2016), effective against avian predators (Guilford, Nicol, Rothschild, & Moore, 1987). Further investigation will be required to determine if odors of Heliconius butterflies act as antipredation signals.…”

The challenge of detecting prey: Private and social information use in predatory bats

“…Even though the conspicuous visual displays of fireflies offer ample opportunity for bats to depredate them, this prey is absent in their diets (Moosman, Cratsley, Lehto, & Thomas, ). Evidence that bats are deterred from consuming fireflies (Moosman et al, ; Vencl et al, ) and can quickly learn to avoid attacking them (Leavell et al, ) supports the long‐standing, but previously untested, hypothesis that the flashing signals fireflies produce for intraspecific communication also serve as aposematic signals to deter predators like bats. Investigations that identify the role that bats may have played in constraining the signals and displays of nocturnal invertebrates that avoid them would be valuable to further understand the intricate ways in which predators shape the communication systems of their prey.…”

Multimodal Aposematic Signals and Their Emerging Role in Mate Attraction

“…In contrast, with a few exceptions (e.g., studies on the dual role of pyrrolizine alkaloids in bella moths Utetheisa ornatrix; Conner et al, 1981), less effort has been made to test the possible multiple functions of chemical compounds in chemical communication between conspecifics and in predator deterrence. One potential chemical group with multiple functions could be pyrazines, a group of compounds that are relatively common in insect defensive fluids (Rothschild et al, 1984;Guilford et al, 1987;Moore et al, 1990;Vencl et al, 2016;Rojas et al, 2017). It is possible that, for example, the intensity of the repulsive odor produced by pyrazines could also function as an honest signal of quality.…”