Quick shift in volatile attraction between the third and fifth instar larvae of Endoclita signifier

Abstract

BACKGROUND Endoclita signifer is a polyphagous lepidopteran species of eucalyptus that selects its hosts in the third‐instar larval period. To understand how it adapts to its host during development, we studied the olfactory responses of late‐stage (fifth)‐instar larvae to the dynamic chemical environment they encounter. RESULTS Thirty‐two volatiles from eucalyptus trunk and soil were identified, among which 14 showed electroantennal activity and five were identified as new. Further behavioral bioassay showed that both β‐pinene and the imitation ratio of six key volatile in eucalyptus trunk were attractive to the fifth‐instar larvae, but both eliminated and increased β‐pinene in the mixture decreased the choice ratio and showed no attraction. Although E. signifer larvae shifted their attraction from o‐cymene at the third‐instar stage to β‐pinene at the fifth‐instar stage in a single volatile, the appropriate ratio of the main compounds in eucalyptus trunk volatile is the key to the behavior choice of fifth‐instar larvae. CONCLUSION The switch in olfactory attraction to different compounds between fifth‐ and third‐instar larvae indicated an olfactory plasticity between third‐ and fifth‐instar larvae. And the particular blend mediated the highly specialized communication interactions specificity between fifth‐instar larvae and eucalyptus trunk volatile indicated the specialized host adaptation to fifth‐instar larvae. This enhances understanding of how the primitive lepidopteran E. signifier, as a native pest, adapts to introduced eucalyptus. Moreover, this study provides knowledge for the screening and development of target volatiles for trapping and managing E. signifer larvae. © 2022 Society of Chemical Industry.

A Study of Adult Olfactory Proteins of Primitive Ghost Moth, Endoclita signifer (Lepidoptera, Hepialidae)

“…Meanwhile, the third instar larvae of E. signifer display a unique behavior pattern: they move from the soil of eucalyptus plantations to standing trees, where they feed on bark and bore into the interior wood. And the phenomenon, along with the damage inflicted by E. signifer on eucalyptus trees within one to three years, indicates that both larval [3,4] and adult host selection contribute to its adaptation to eucalyptus. And because the sensitive olfactory system of the insect plays a key role in host selection, mating, and feeding, we hypothesized that the olfactory system of adult E. signifer significantly contributes to its host selection, with olfactory proteins serving as the functional components in this process.…”