Microorganisms within insects play a vital role in maintaining the basal physiological functions of the insects, with olfactory signals as critical components of insect survival strategies. Leptocybe invasa (L. invasa), an invasive alien pest inflicting significant damage to eucalyptus trees, harbors a rich and varied bacterial community within its body. However, the impact of its endogenous bacteria and their microbial Volatile Organic Compounds (mVOCs) on the behavioral preferences of L. invasa remains unexplored to date. This study focused on nine cultivable and dominant endogenous bacterial strains within L. invasa. Using a Y-tube olfactometer, we investigated the behavioral responses of female L. invasa to the mVOCs emitted by these bacteria. Concurrently, gas chromatography–mass spectrometry (GC–MS) was employed to quantify the mVOCs produced by these endogenous bacteria. Our findings revealed that Staphylococcus sp. exhibited the highest attractiveness of L. invasa, whereas Microbacterium sp. and E. cloacae exerted the most significant avoidance effects. The analysis of the mVOCs further highlighted the significance of aldehyde compounds, notably 2,3,6-trichlorobenzaldehyde, and alkane compounds, such as eicosane, in mediating the repellency and attraction effects. These results contribute to a deeper understanding of the invasion mechanism of L. invasa and provide a scientific basis for developing novel biopesticides or elicitors.

Various types of sensilla are densely distributed on the antennal surfaces of insects. The specialization of perception and ecological adaptability of antennae in detecting external environmental signals are reflected in the morphology, function, number, and distribution pattern of sensilla. L. invasa, O. bipolaris, and O. maskelli are three types of wasps that harm eucalyptus trees. To investigate the perception and reception methods of chemical signals from eucalyptus trees by the three gall wasps and compare interspecific differences, the antennal morphology and sensillar characteristics of these three gall wasps were systematically analyzed using scanning electron microscopy, including sensillar length, type, distribution, and number. Knee-shaped antennae, comprising the radicle, scape, pedicel, anelli, funicle, and club, are present in all three species. However, significant interspecific differences were observed in total antennal length and funicular number. Five major sensilla categories, comprising nine subtypes, were identified. Among these, five types (BS, CH, CS, TSI, TSII) were common to all three gall wasp species. PSI and PSII were unique to L. invasa, while O. bipolaris and O. maskell shared PSIII. Compared to O. maskelli, O. bipolaris possessed a significantly greater number of PSIII sensilla, which were also longer. TSIII was found exclusively in O. bipolaris. Interspecific differences were evident in antennal morphology, as well as in the number, size, and distribution of the sensilla. These variations in sensilla and antennal shape serve as a morphological foundation for species identification in addition to reflecting ecological adaptation and functional differentiation in environmental signal perception.