Distribution and morphometric studies on antennal sensilla of female and male Pediobius imbreus (Hymenoptera: Eulophidae)

The insect parasitoid, Pediobius imbreus (Hymenoptera: Eulophidae), which has a diverse host range, probably possesses various antennal sensilla (sensory organs) to assist the parasitoid in host searching and ensuring its survival. In this study, we aimed to investigate the distribution and morphology of the antennal sensilla of both female and male P. imbreus using scanning electron microscopy (SEM). SEM results revealed that P. imbreus has seven antennomeres on its geniculate antenna, which is composed of scape, pedicel, and five flagellomeres. Numerous antennal sensilla types were observed on the P. imbreus antennae: trichoid sensilla types 1-8; placoid sensilla types 1-2; and basiconic sensilla. The female P. imbreus exhibits a greater abundance of sensilla on both its dorsal and ventral surfaces compared to the male. The trichoid sensilla are the most abundant sensillum type found on the antennae of P. imbreus, followed by placoid sensilla and basiconic sensilla. By comparison, the female P. imbreus have more diverse types of sensilla, which are longer than that of male. Overall, the female antenna and its trichoid sensilla type 6 are significantly (P < 0.05) longer than that of the male. The male P. imbreus does not have trichoid sensilla type 8 and placoid sensilla type 2. The potential roles of the antennal sensilla in host detection based on their location and morphology will be discussed. The knowledge obtained will aid future research on the host localization in P. imbreus.