Environmentally vulnerable noble chafers exhibit unusual pheromone-mediated behaviour

Abstract

Conserving populations of environmentally vulnerable insect species requires a greater understanding of the factors that determine their abundance and distribution, which requires detailed knowledge of their population and community ecology. Chemical ecological tools such as pheromones can be used for non-destructive monitoring of scarab beetle populations, enabling European countries to detect and, in some cases, map the range of some of these species, proving a valuable technique for monitoring elusive saproxylic beetles. In this paper, we investigated the behavioural and chemical ecology of the noble chafer, Gnorimus nobilis L., a model insect species of conservation concern across a Europe-wide distribution, and a red-listed UK Biodiversity Action Plan priority species. We identified a potential pheromone of adult beetles using electrophysiological recordings, behavioural measurements and field trials in the UK. Gnorimus nobilis is highly unusual in that although both sexes produce, at high metabolic cost, the natural product 2-propyl (E)-3-hexenoate, it only attracts males. This pattern of chemical signalling makes the classification of the compound, based on current semiochemical terminology, somewhat problematic, but in our view, it should be termed an aggregation pheromone as a consequence of the production pattern. Since both sexes emit it, but apparently only males respond positively to it, 2-propyl (E)-3-hexenoate may reflect an intermediate evolutionary stage towards developing into a sex-specific signal. From an applied perspective, our study provides a model for the non-invasive surveillance of cryptic vulnerable insect species, without the need for habitat searching or disturbance, and continuous human monitoring.

Contrasting Volatilomes of Livestock Dung Drive Preference of the Dung Beetle Bubas bison (Coleoptera: Scarabaeidae)

“…Although eucalyptol and limonene reportedly elicit antennal responses in another species of dung beetle (O. binodis) [40], no apparent role of these VOCs in attracting B. bison was noted. However, the degree of attractiveness of odor sources for beetles can be influenced by the differential abundance and/or ratios of components as well as the concentration of VOCs regardless of the number of components in a blend [43,44]. Further work focused on quantification of dung VOCs and dose-dependent EAG studies are required to assess the importance of compound abundance and ratios involved in dung beetle attraction and discrimination.…”

Characterisation of Antennal Sensilla and Electroantennography Responses of the Dung Beetles Bubas bison, Onitis aygulus and Geotrupes spiniger (Coleoptera: Scarabaeoidea) to Dung Volatile Organic Compounds

“…The EAG technique used in this study was similar to that previously described in the literature [60][61][62] and recordings were conducted only with female antennae (n = 3-11). Adult beetles were starved overnight and kept at 4 • C for 15 min to reduce their activity before dissection.…”

Characterizing human odorant signals: insights from insect semiochemistry and in silico modelling

“…This approach has the disadvantage of a relatively small part of the headspace being sampled and the sample is directly eluted into the GC apparatus, precluding multiple analysis, for example, of the chemical composition and biological activity [7]. The most successful approach is by the entrainment of air from above the biological sample (Figure 3) and by drawing the air through a porous polymer and eluting with a purified solvent, to obtain a liquid sample for multiple types of analysis [6]. For long-term storage, the sample must be sealed in a glass ampoule under an inert gas, preferably nitrogen.…”

“…those for reverse-phase liquid chromatography [5], can be used to extract human skin volatiles directly, and then either be eluted with solvent or the volatiles desorbed by a flow of inert gas for analysis. For identifying insect pheromones as they are released into the air above an insect, entrainment onto a porous polymer is most effective and can accurately measure the naturally released pheromone composition [6]. A very simple system employs solid-phase microextraction (SPME) such as by a retractable absorbent polymer fibre, which is exposed to the headspace above the pheromone-releasing insect and combined as a syringe device for direct insertion for gas chromatographic (GC) analysis [7].…”