Comparative morphology of sensilla on mole cricket antennae and palps

Mole crickets (Orthoptera: Gryllotalpidae: Scapteriscus spp.) are notorious tunneling and root-feeding pests of turfgrass on golf courses and sports fields in the southern U.S. They appear to sense and avoid insecticides and insect pathogens in greenhouse and field tests, but little is known about how the chemical cues are detected by this nocturnal insect. Our objective was to describe the external morphology, number, and distribution of sensilla on the antennae and palps of male and female S. borellii (Giglio-Tos) and S. vicinus (Scudder). Ten males and ten females of each species were collected from pastures in northcentral Florida in 2007, cleaned in an ultrasound bath, and dehydrated in an alcohol series. The head and thorax were dried by the critical point drying method, coated with gold/paladium, and antennae and palps were examined with a tungsten low vacuum scanning electron microscope. Sensilla were counted on ten proximal, mid- and distal antennal segments. Six types of sensilla were observed, including sensilla basioconica (olfactory receptors), s. chaetica (two types, mechanoreceptors and contact chemoreceptors), s. coeloconica (two types, hygroreceptors), and s. campaniformia (proprioreceptors). About 300 sensilla of different types were found per 13,000 ìm² on the palps, but transmission electron microscope observations are needed for greater clarity. Types and number of sensilla did not differ between mole cricket species and sexes. Mole cricket antennae appear to be primarily olfactory organs, and maxillary and labial palps are responsible for contact chemoreception.