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

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. The difference in olfactory recognition between fifth‐ and third‐instar larvae indicated strong olfactory plasticity in E. signifer larvae.