Experimental evidence for female mate choice in a noctuid moth

Interaction between females and males grapevine moth Lobesia botrana modifies further mating preference

During reproduction, females may boost their fitness by being selective based on direct material benefits provided by the males, such as nuptial gifts. In Lepidoptera, male provides a spermatophore containing nutrients. However, virgin males produce a bigger spermatophore, containing spermatozoa and nutrients, allowing higher female fertility. Lepidoptera females that could detect the sexual status of males may thus prefer a male without previous mating experience (i.e. a virgin male). This mate selection could be achieved by the use of chemical indices, such as sexual pheromones and cuticular compounds, known to be possibly exchanged during reproduction, and which can be indicators of a previous mating experience and known to be possibly sources of information exchanged. In this study, we experimentally presented Lobesia botrana virgin males with females in order for them to be exposed to females' natural sexual pheromones or cuticular compounds. 12 or 48 h after the exposure of males to either females' sexual pheromones or cuticular compounds, these males were confronted to naïve females, which have a choice between them or a virgin non-exposed males. We highlighted that, despite producing a spermatophore of similar volume, all exposed virgin males were less likely to mate with females 12 h after exposure, while after 48 h of exposure this is only the case for virgin males exposed to sexual pheromones. L. botrana females may thus discriminate male sexual experience based on chemical cues (either from cues transferred directly from females to males, or from changes in the cuticular or pheromone males' profile) indicating past mating experiences. Mating duration was longer for males exposed to sexual pheromones after 12 h only, and for males exposed to cuticular compounds after 48 h only. Pheromones signal might be more persistent over time and seems to more easily gather information for males. The physiological reasoning behind this result still needs to be investigated.

Lateralised courtship behaviour and its impact on mating success in Ostrinia furnacalis (Lepidoptera: Crambidae)

Lateralisation is a well-established phenomenon observed in an increasing number of insect species. This study aims to obtain basic details on lateralisation in courtship and mating behaviour in Ostrinia furnacalis, the Asian corn borer. We conducted laboratory investigations to observe lateralisation in courtship and mating behaviours in adult O. furnacalis. Our goal was also to detect lateralised mating behaviour variations during sexual interactions and to elucidate how these variances might influence the mating success of males. Our findings reveal two distinct lateralised traits: male approaches from the right or left side of the female and the direction of male turning displays. Specifically, males approaching females from their right side predominantly exhibited left-biased 180° turning displays, while males approaching females from the left-side primarily displayed right-biased 180° turning displays. Notably, left-biased males, executing a 180° turn for end-to-end genital contact, initiated copulation with fewer attempts and began copulation earlier than their right-biased approaches with left-biased 180° turning displays. Furthermore, mating success was higher when males subsequently approached the right side of females during sexual encounters. Left-biased 180° turning males exhibited a higher number of successful mating interactions. These observations provide the first report on lateralisation in the reproductive behaviour of O. furnacalis under controlled laboratory conditions and hold promise for establishing reliable benchmarks for assessing and monitoring the quality of mass-produced individuals in pest control efforts.

The Evolutionary Importance of Intraspecific Variation in Sexual Communication Across Sensory Modalities

The evolution of sexual communication is critically important in the diversity of arthropods, which are declining at a fast pace worldwide. Their environments are rapidly changing, with increasing chemical, acoustic, and light pollution. To predict how arthropod species will respond to changing climates, habitats, and communities, we need to understand how sexual communication systems can evolve. In the past decades, intraspecific variation in sexual signals and responses across different modalities has been identified, but never in a comparative way. In this review, we identify and compare the level and extent of intraspecific variation in sexual signals and responses across three different modalities, chemical, acoustic, and visual, focusing mostly on insects. By comparing causes and possible consequences of intraspecific variation in sexual communication among these modalities, we identify shared and unique patterns, as well as knowledge needed to predict the evolution of sexual communication systems in arthropods in a changing world.

Mutagenesis of Odorant Receptor Coreceptor Orco Reveals the Odorant-Detected Behavior of the Predator Eupeodes corollae

The successful mating of the hoverfly and the search for prey aphids are of great significance for biological control and are usually mediated by chemical cues. The odorant receptor co-receptor (Orco) genes play a crucial role in the process of insect odor perception. However, the function of Orco in the mating and prey-seeking behaviors of the hoverfly remains relatively unexplored. In this study, we characterized the Orco gene from the hoverfly, Eupeodes corollae, a natural enemy insect. We used the CRISPR/Cas9 technique to knock out the Orco gene of E. corollae, and the EcorOrco-/- homozygous mutant was verified by the genotype analysis. Fluorescence in situ hybridization showed that the antennal ORN of EcorOrco-/- mutant lack Orco staining. Electroantennogram (EAG) results showed that the adult mutant almost lost the electrophysiological response to 15 odorants from three types. The two-way choice assay and the glass Y-tube olfactometer indicated that both the larvae and adults of hoverflies lost their behavioral preference to the aphid alarm pheromone (E)-β-farnesene (EBF). In addition, the mating assay results showed a significant decrease in the mating rate of males following the knock out of the EcorOrco gene. Although the mating of females was not affected, the amount of eggs being laid and the hatching rate of the eggs were significantly reduced. These results indicated that the EcorOrco gene was not only involved in the detection of semiochemicals in hoverflies but also plays a pivotal role in the development of eggs. In conclusion, our results expand the comprehension of the chemoreceptive mechanisms in the hoverflies and offers valuable insights for the advancement of more sophisticated pest management strategies.

Diet-derived male sex pheromone compounds affect female choice in a noctuid moth

Sexual signals often function in species recognition and may also guide mate choice within a species. In noctuid moths, both males and females may exercise mate choice. Females of the tobacco budworm Chloridea virescens prefer to mate with larger males, but the signal(s) underlying female choice remain unknown. Male hairpencil volatiles are emitted during close range courtship displays. However, previously identified male hairpencil volatiles, namely acetate esters, aldehydes, alcohols, and fatty acids, are not associated with female choice. Recently, two new hairpencil compounds were identified that elicit strong electrophysiological responses in female antennae: methyl salicylate (MeSA) and δ-decalactone. In this study, we investigated the effect of larval diet and adult feeding on MeSA and δ-decalactone content in hairpencils and determined whether these compounds are involved in female choice. We found that larval diet affected MeSA content in hairpencils, but not δ-decalactone. Conversely, adult feeding affected the level of δ-decalactone, but not MeSA: sugar-water feeding increased δ-decalactone content compared to plain water. In two-choice assays, females mated more with males that had higher amounts of δ-decalactone, and less with males with higher amounts of MeSA.

Mating status affects female choice when females are signalers

Sexual selection in animals has been mostly studied in species in which males are signalers and females are choosers. However, in many species, females are (also) signalers. In species with non‐signaling females, virgin females are hypothesized to be less choosy than mated females, as virgins must mate to realize fitness and the number of available males is generally limited. Yet, when females signal to attract males, mate limitation can be overcome. We tested how virgin and mated females differ in their calling behavior, mating latency, and in mate choice, using the tobacco budworm Chloridea (Heliothis) virescens as an example for a species in which females are not only choosers but also signalers. We found that virgin females signaled longer than mated females, but virgin and mated signaling females were equally ready to mate, in contrast to non‐signaling females. However, we found that virgin signaling females showed weaker mate preference than mated females, which can be explained by the fact that females increase their fitness with multiple matings. Mated females may thus further increase their fitness by more stringent mate selection. We conclude that signaling is a crucial aspect to consider when studying female mate choice because signaling may affect the number of available mates to choose from.