Microstructural Adaptation for Prey Manipulation in the Millipede Assassin Bugs (Hemiptera: Reduviidae: Ectrichodiinae)

SIMPLE SUMMARY: The millipede assassin bugs are well known for their prey specialization. In this study, we examined the fine structures of the antennae, mouthparts, and legs of four genera and species of ectrichodiines using a scanning electronic microscope and compared them with those in Tribelocephalinae, a lineage closely related to Ectrichodiinae. We found that ectrichodiines possess distinctly more slightly transverse ridges on the mandibles, which probably facilitate stabilizing mandibular stylets in prey tissues. The small papillae on the legs are considered to adapt to immobilize millipedes. Overall, our study illustrates, at a microstructural level, the remarkable morphological adaption of prey manipulation in ectrichodiines, which will facilitate future studies on the adaptive evolution of feeding habits in Reduviidae. ABSTRACT: Species in Ectrichodiinae are known for their prey specialization on millipedes. However, knowledge of the morphological adaptations to this unique feeding habit was limited. In the current study, we examined the microstructures of the antennae, mouthparts, and legs of four millipede feeding ectrichodiines, Ectrychotes andreae (Thunberg, 1888), Haematoloecha limbata Miller, 1953, Labidocoris pectoralis (Stål, 1863), and Neozirta eidmanni (Taueber, 1930), and compared them with those of three species of tribelocephalines, a group closely related to Ectrichodiinae. On the antennae, we found four types of antennal sensilla. On the mouthparts, we recognized four types of labial sensilla. Sampled ectrichodiines have distinctly more and denser slightly transverse ridges on the external side of mandibles than tribelocephalines. E. andreae and H. limbata possess numerous small papillae fringed with densely arranged finger-print-like grains on the trochanter and femur; these probably facilitate the immobilization of prey. Overall, our study illustrates, at a microstructural level, the remarkable morphological adaption of prey manipulation in ectrichodiine, and has enhanced our understanding about stenophagy in the family Reduviidae.