Abstract
Simple SummaryAphids are severe pests on many plants, and understanding their olfactory-guided behaviour is essential for the development of alternative management strategies. The pea aphid, Acyrthosiphon pisum, is a good model to understand the influence of different factors on olfactory-guided behaviour, because it encompasses several biotypes, each specialised on different legumes, and harbours different facultative symbionts that influence the insect hosts in many ways. We investigate here whether the aphid genotype and facultative symbionts influence behavioural and antennal responses to the alarm pheromone E-β farnesene in pea aphids. This alarm pheromone is released in case of danger and elicits escape behaviour of conspecifics. For that, we used different pea aphid clones specialised on different host plants and derived lines that harbour or not facultative endosymbiotic bacteria. In behavioural assays, we found that, indeed, aphid genotypes respond differentially to E-β farnesene, whereas the presence of an endosymbiont conferring protection against natural enemies does not modify responses to the alarm pheromone. Electrophysiological recordings from the olfactory organ, the antenna, revealed significant differences in sensitivity between aphid genotypes but not as a function of endosymbionts, corresponding to the behavioural results.Aphids use an alarm pheromone, E-β farnesene (EBF), to warn conspecifics of potential danger. The antennal sensitivity and behavioural escape responses to EBF can be influenced by different factors. In the pea aphid, Acyrthosiphon pisum, different biotypes are adapted to different legume species, and within each biotype, different genotypes exist, which can carry or not Hamiltonella defensa, a bacterial symbiont that can confer protection against natural enemies. We investigate here the influence of the aphid genotype and symbiotic status on the escape behaviour using a four-way olfactometer and antennal sensitivity for EBF using electroantennograms (EAGs). Whereas the investigated three genotypes from two biotypes showed significantly different escape and locomotor behaviours in the presence of certain EBF doses, the infection with H. defensa did not significantly modify the escape behaviour and only marginally influenced the locomotor behaviour at high doses of EBF. Dose-response curves of EAG amplitudes after stimulation with EBF differed significantly between aphid genotypes in correlation with behavioural differences, whereas antennal sensitivity to EBF did not change significantly as a function of the symbiotic status. The protective symbiont H. defensa does thus not modify the olfactory sensitivity to the alarm pheromone. How EBF sensitivity is modified between genotypes or biotypes remains to be investigated.
Highlights
Aphids secrete an alarm pheromone, E-β farnesene (EBF), emitted at the cornicles and common to many species, to warn conspecifics of potential danger, such as, for example, the approach of natural enemies [1]
Many aphids host facultative bacterial symbionts that confer a protection against natural enemies [5] but which may alter the responses to EBF as a side effect of the symbiont infection or as a way to reduce unnecessary costly defences
We studied here if the avoidance behaviour and antennal detection of EBF vary between three genotypes of A. pisum deprived of secondary symbionts, one genotype specialised on G. tinctoria, and two genotypes of the biotype specialised on M. sativa
Summary
Aphids secrete an alarm pheromone, E-β farnesene (EBF), emitted at the cornicles and common to many species, to warn conspecifics of potential danger, such as, for example, the approach of natural enemies [1]. Aphid species and populations are not exposed to the same predation risks, which may select for different responses to EBF [2]. Many aphids host facultative bacterial symbionts that confer a protection against natural enemies [5] but which may alter the responses to EBF as a side effect of the symbiont infection (i.e., cost of carrying the symbiont) or as a way to reduce unnecessary costly defences (e.g., defensive behaviours and alarm pheromone emission). The pea aphid, Acyrthosiphon pisum Harris (Hemiptera, Aphididae), is an excellent model to study the factors that may cause variations of responses to EBF for several reasons. The sensory mechanisms underlying EBF detection have been investigated. Like other aphid species, the pea aphid reproduces parthenogenetically during most of its annual life cycle, and clonal individuals can be obtained for experiments, which facilitates the dissection of genetic and environmental components of phenotypic variation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
