Antennal Morphology of Two Specialist Predators of Hemlock Woolly Adelgid, <I>Adelges tsugae</I> Annand (Homoptera: Adelgidae)

Abstract

We used scanning and transmission electron microscopy in a morphological examina- tion of the antennae of two specialist predators of the exotic hemlock woolly adelgid, Adelges tsugae Annand, as an initial step toward understanding the potential importance of olfaction in host-Þnding behavior. Laricobius nigrinus Fender (Coleoptera: Derodontidae) possesses six types of sensilla on a relatively long antennae comprised of scape, pedicel, and nine annuli. Two types of basiconic sensilla contained numerous wall pores with branching pore kettles and were located on the terminal three annuli. The terminal annulus contained a placoid-like sensillum, and the penultimate and antepen- ultimate annuli contained a coeloconic-type sensillum forming a ring around the distal portion. Two types of sensilla chaetica were located along much of the length of the antennae. Pseudoscymnus tsugae Sasaji and McClure (Coleoptera: Coccinellidae) was found to possess Þve types of sensilla on an extremely short antenna, which is characteristic of the tribe Scymnini, consisting of scape, pedicel, and seven annuli. Three of the annuli were void of sensilla. Two types of sensilla chaetica were located on the scape and pedicel, as well as the terminal annuli. Three types of basiconic sensilla, one of which contained numerous wall pores, were identiÞed on the terminal two annuli. No sexual dimorphism was detected on either predator species. Our results suggest that olfaction is a more important sensory modality in L. nigrinus than P. tsugae, and that trap-based sampling methods incorporating olfactory cues are more likely to be successful for L. nigrinus than P. tsugae.