Fine structure of mouthparts and forelegs of Euplatypus parallelus (Coleoptera: Curculionidae) with emphasis on the behavior of gallery excavation.

Euplatypus parallelus (F.) (Coleoptera: Curculionidae) is one of the most invasive species of all the Platypodinae. It penetrates the xylem and oviposits in its host trees thereby weakening the trunk causing them to break under extreme conditions. Since the beetle has evolved effective drilling mouthparts enough to make wood tunnels, we used a field emission scanning electron microscopy to describe the sexual difference in mouthparts and forelegs morphology of the beetle. E. parallelus has chewing type mouthparts composed of a labrum, a pair of mandibles, a pair of maxillae, and a labium. In females, the size of maxillary palpi, submentum, prementum, and labial palpi are significantly larger than males. E. parallelus forelegs were walking type composed of procoxa, protrochanter, profemur, protibia, protarsus, and propretarsus. We observed no significant differences between the forelegs of males and females, but the procoxa of the males was slightly larger than that of females. The structural differences in mouthparts and forelegs between females and males indicated that females invest more time in gallery excavation than males. Possible functional relationships of these structures are discussed. These studies revealed the mechano-dynamic characteristics of E. parallelus and provided a theoretical basis for exploring the behavior of this beetle.