Cuticular hydrocarbon variation among Rhagoletis fruit flies (Diptera: Tephritidae): implications for premating reproductive isolation and ecological speciation

Abstract

1. Fruit flies in the genus Rhagoletis are a model for ecological speciation via sympatric host plant shifting. Rhagoletis mate on or near the fruit of their respective host plants, generating premating reproductive isolation between taxa specialised on different hosts. However, non‐host‐related premating isolation has been observed between some Rhagoletis species associated with morphological differences in body colour and wing patterns. 2. Here, the extent of epicuticular hydrocarbon (CHC) variation as a possible, additional determinant of mate choice in adults of six Rhagoletis taxa, including the apple and hawthorn‐infesting host races of R. pomonella is investigated. 3. Gas‐chromatography‐mass‐spectrometry revealed 36 repeatable and quantifiable hydrocarbon components present on the epicuticles of all six fly taxa, comprised of at least 53 different CHC compounds, with chain lengths varying from 27 to 34 carbon atoms, consisting of n‐alkanes, mono‐, dimethyl‐, and trimethyl‐alkanes, alkenes, and alkadienes. There were significant differences in the relative proportions of CHCs between adult R. cingulata, R. cornivora, R. zephyria, R. mendax, and R. pomonella, as well as between the apple‐ and hawthorn‐infesting host races of R. pomonella. Furthermore, within the R. pomonella host races and R. mendax, significant CHC differences were observed between the sexes and across collecting sites. 4. The results are consistent with variation in CHCs potentially contributing to observed patterns of premating isolation between Rhagoletis taxa, possibly due to combination of sexual and host‐related selection, which will necessitate further, in depth chemical analyses and future mating trials to substantiate.

The role of sexual isolation during rapid ecological divergence: Evidence for a new dimension of isolation in Rhagoletis pomonella

“…For instance, temperature can affect the expression of cuticular hydrocarbons (CHCs) (Ingleby et al, 2014), a known mating signal in other insect species (e.g., Drosophila Etges & Jackson, 2001, leaf beetles Zhang et al, 2014, crickets Mullen et al, 2007, and walking sticks Schwander et al, 2013). In Rhagoletis pomonella , CHCs are a putative mating signal, and CHC profiles differ between apple and hawthorn flies (Hood et al, 2021). Moreover, recent research suggests a possible connection between diapause life history timing, which is known to be heavily influenced by temperature (i.e., Feder et al, 2010; Lackey et al, 2022) and brain development in R. pomonella (Kharva et al, 2022).…”

Improving Natural Enemy Selection in Biological Control through Greater Attention to Chemical Ecology and Host-Associated Differentiation of Target Arthropod Pests

“…Some natural enemy species, such as parasitoids, also rely on CHCs to identify their host species for oviposition [98,99]. Although only one study to date has connected prey HAD to changes in CHCs [100], we postulate that this is likely a common scenario, and the extent to which CHCs diverge within prey populations could determine whether natural enemy HAD will also occur. Divergent pheromone emissions could play roles in natural enemy HAD and efficacy, which should be considered in efforts for natural enemy encouragement in classical biological control.…”