Comparison of Morphological Characteristics of Antennae and Antennal Sensilla Among Three Species of Gall Wasps (Hymenoptera: Eulophidae)

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. <i>L. invasa</i>, <i>O. bipolaris</i>, and <i>O. maskelli</i> 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 <i>L. invasa</i>, while <i>O. bipolaris</i> and <i>O. maskell</i> shared PSIII. Compared to <i>O. maskelli</i>, <i>O. bipolaris</i> possessed a significantly greater number of PSIII sensilla, which were also longer. TSIII was found exclusively in <i>O. bipolaris</i>. 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.