Density-dependent olfactory responses of Ectropis obliqua to tea plant volatiles induced by Empoasca pirisuga

Abstract

Introduction Tea plants (Camellia sinensis) are persistently threatened by multiple co-occurring herbivore pests. Empoasca pirisuga and Ectropis obliqua are two dominant species in tea plantations, and the alternation of their population dominance is driven by complex ecological mechanisms that remain poorly characterized. This study aimed to characterize density-dependent olfactory responses of E. obliqua to herbivore-induced plant volatiles (HIPVs) from tea plants infested by E. pirisuga under laboratory conditions. Methods Headspace volatile profiles induced by six graded densities of E. pirisuga were identified and quantified via gas chromatography–mass spectrometry (GC-MS) with solid-phase microextraction (SPME). Multivariate analyses (PERMANOVA and PCA) were used to assess global differences in volatile blends. Olfactory responses of virgin female E. obliqua adults to induced volatiles and to synthetic candidate compounds were assessed using a Y-tube olfactometer with clean air or hexane solvent as the reference control. Results Infestation density significantly altered the composition and relative abundance of tea plant HIPV blends (PERMANOVA, P < 0.001). β-ocimene, methyl jasmonate (MeJA) and methyl salicylate (MeSA) were identified as the three major density-responsive components. E. obliqua exhibited a clear density-dependent valence shift in response to induced HIPVs relative to clean air: low-density infestation produced blends that significantly attracted E. obliqua, whereas high-density infestation elicited strong repellency. Synthetic compound bioassays confirmed that β-ocimene and MeJA function as individual attractants, while MeSA acts as an individual repellent for virgin female E. obliqua under laboratory conditions. Discussion These findings demonstrate that density-dependent modulation of HIPV blends is associated with interspecific olfactory responses between E. pirisuga and E. obliqua under controlled laboratory conditions. This work provides a chemical basis for hypotheses regarding pest dominance alternation in tea agroecosystems, which require further field validation including oviposition, colonization and population-level assays.