Olfactory responses of Argentine stem weevil to herbivory and endophyte-colonisation in perennial ryegrass

Abstract

Argentine stem weevil adults (ASW, Listronotus bonariensis) feed on the leaves of agricultural grasses and their larvae mine the pseudostem, causing extensive damage that can result in plant death. Plants emit volatiles that serve as signals to host-searching insects and these odours can be altered by both herbivory and fungal endophyte-infection. This study investigated whether ASW adults utilise olfaction to identify their host plants, perennial ryegrass (Lolium perenne), and if conspecific herbivory or the presence of Epichloë festucae var. lolii fungal endophytes (strain wild-type or AR1) influenced such responses. Results from olfactometer bioassays established that ASW adults were able to utilise their olfactory response to orient towards volatiles released by perennial ryegrass and further, the weevils displayed a preference for plants previously damaged by conspecific weevils. However, there was no evidence that weevils had the ability to distinguish between endophyte-infected and endophyte-free plants using olfaction alone. Using a push–pull extraction technique, thirteen volatile compounds were identified in the blend released by perennial ryegrass. Endophyte and herbivory were found to alter these volatile compounds and quantities emitted by this forage grass. This study suggests that despite observing differences in the plant volatile blend, ASW do not perceive endophyte (wild-type and AR1) using olfaction alone and must rely on other cues, e.g. contact chemoreception or post-ingestional malaise, to detect the presence of a bioactive endophyte in an otherwise acceptable host plant.

Scents and sensibility: Best practice in insect olfactometer bioassays

“…Behaviour in relation to the stimulus or stimuli is scored in one of several ways: counting study subjects moving toward or touching a stimulus, time spent by study subjects within a pre‐determined distance of the stimulus, or time taken for study subjects to respond to the stimulus (Knolhoff & Heckel, 2014). Although many studies have successfully used still air olfactometers for different insect taxa (e.g., Weeks et al, 2011; Hennessy et al, 2022; Pouët et al, 2022), there are experimental limitations to using this apparatus.…”

Overview of biofertilizers in crop production and stress management for sustainable agriculture

“…in a variety of grass species is one of the well-known secondary metabolites produced by endophytic fungi. Hennessy et al ( 2022 ) reported Epichloe festucae colonized agricultural forage grasses and offered the plant defense against herbivorous insects. Streptomyces hydrogenans metabolites can be used as safe biocontrol agents against Meloidogyne incognita and plant growth promoters for Solanum lycopersicum (Sharma et al, 2020 ).…”

Insect-Microorganism Interaction Has Implicates on Insect Olfactory Systems

“…In D. melanogaster, DA2 activation by geosmin could override the inputs of other olfactory pathway signals that affect oviposition and feeding. Odorants produced by fungi themselves could impact the behavioral reactions of insects by affecting the input, transmission, and transfer of feedback of olfactory information [49]. Formosan subterranean termites, Coptotermes formosanus, exhibit aversive reactions to 3-octanone and 1-octen-3-ol, which are the major chemical compounds of Isaria fumosorosea K3 [50].…”