Caterpillar-induced plant volatiles attract conspecific adults in nature

Abstract

Plants release volatiles in response to caterpillar feeding that attract natural enemies of the herbivores, a tri-trophic interaction which has been considered an indirect plant defence against herbivores. The caterpillar-induced plant volatiles have been reported to repel or attract conspecific adult herbivores. To date however, no volatile signals that either repel or attract conspecific adults under field conditions have been chemically identified. Apple seedlings uniquely released seven compounds including acetic acid, acetic anhydride, benzyl alcohol, benzyl nitrile, indole, 2-phenylethanol, and (E)-nerolidol only when infested by larvae of the light brown apple moth, Epiphyas postvittana. In field tests in New Zealand, a blend of two of these, benzyl nitrile and acetic acid, attracted a large number of conspecific male and female adult moths. In North America, male and female adults of the tortricid, oblique-banded leafroller, Choristoneura rosaceana, were most attracted to a blend of 2-phenylethanol and acetic acid. Both sexes of the eye-spotted bud moth, Spilonota ocellana, were highly attracted to a blend of benzyl nitrile and acetic acid. This study provides the first identification of caterpillar-induced plant volatiles that attract conspecific adult herbivores under natural conditions, challenging the expectation of herbivore avoidance of these induced volatiles.

Trapping Pandemis limitata (Lepidoptera: Tortricidae) moths with mixtures of acetic acid, caterpillar-induced apple-leaf volatiles, and sex pheromone

“…Volatilised acetic acid was emitted through a 3-mm-diameter hole drilled in the lid of each vial. This acetic acid release device, hereafter referred to as our standard acetic-acid co-lure, was modified after Landolt et al (2007) and used by El-Sayed et al (2016). Red natural rubber septa (VWR International, Mississauga, Ontario, Canada) were used to release phenylacetonitrile, 2-phenylethanol, and pheromone alone and in combination in various experiments .…”

“…El-Sayed et al (2016) suggested that combining caterpillar-induced benzenoid-based kairomones with sex pheromone might increase catches of male tortricid moths. However, we found that adding acetic acid + 2-phenylathanol to the sex pheromone of P. limitata significantly reduced male moth catch.…”

“…Yet, when phenylacetonitrile and 2-phenylethanol were individually combined with acetic acid, each binary blend caught a similar number of moths and each caught significantly more moths than their individual components (Giacomuzzi et al 2016). In a similar study focussed on the North American tortricid species, Spilonota ocellana (Denis and Schiffermüller) and C. rosaceana, El-Sayed et al (2016) recorded incidental catches of two nontarget species, P. limitata and P. pyrusana, using binary blends of acetic acid and these same aromatic benzenoids. Collectively, these studies suggest it may be feasible to develop kairomone-based lures for trapping female P. limitata that could be beneficial for organic apple producers.…”

Importance of trap liner adhesive selection for male moth catch (Lepidoptera: Tortricidae) with bisexual attractants

“…Light and Knight () demonstrated that female Cydia pomonella (L.), captured in pear ester, ethyl ( E,Z )‐2,4‐decadienoate‐baited traps were not responsible for male captures by using buckets traps with a drowning liquid. More recently, El‐Sayed, Knight, Byers, Judd, and Suckling () speculated that the attraction of various female tortricids to traps baited with acetic acid and either phenylacetonitrile or 2‐phenylethanol was due to a host plant cue for oviposition and that the capture of males in these traps (typically at a 1:1 sex ratio in traps largely using SG liners) could be due to females calling from the liner, but provided no data to support this hypothesis. However, an earlier study (A.L.…”

Index of host habitat preference explored by movement‐based simulations and trap captures

“…Lygus plant bugs (Miridae) disperse from less preferred cotton hosts to the preferred host alfalfa (Bancroft, ). Olfactory mechanisms appear to aid moths, bark beetles, parasitoid wasps and many other insects in finding and staying in host habitat by means of attraction to pheromones and host plant volatiles (Byers, ; Byers et al., ; Cotes et al., ; El‐Sayed et al., , ; Landolt & Phillips, ; Quilici & Rousse, ; Vet, ; Zhao & Kang, ). Many insects appear to have evolved behaviour to search in a random forward direction for host habitats until finding appropriate odour of host plants or insects (Byers, , , , , ; Levi−Zada et al., ).…”