Antennal Sensilla of Acrididae (Orthoptera) in Relation to Subfamily and Food Preference

Abstract

The external structure, abundance, and distribution of sensilla on the antennae of 55 species of acridids were investigated using scanning electron microscopy. Melanoplinae, Oedipodinae, Gomphocerinae, Cyrtacanthacridinae, Acridinae, and Romalinae were represented. Species were grouped into forbivorous (broad-leaf herbs), ambivorous (about equal amounts of forbs and grasses), graminivorous (grasses), and univorous (single species or related genera) feeding groups. The mean number of sensilla per antenna was 2,722 (range, 708-8,500) and the mean per segment was 120 (32-354). The mean number and range per antenna of each sensillum type were as follows: long basiconic, 454 (84-1,258); short basiconic, 911 (8-4,198); slender short basiconic, 283 (0-2,170); coeloconic, 1,053 (204-4,102); and trichoid, 21 (0-252). In the three major subfamilies, long basiconic sensilla were similar in number; the number of short basiconic sensilla was low in Melanoplinae; the number of slender short basiconic sensilla and coeloconic sensilla was low in Gomphocerinae; and trichoid sensilla were few in Melanoplinae and numerous in Oedipodinae. Oedipodines averaged 2,958 sensilla, gomphocerines 2,780, and melanoplines 2,347. Data are presented for sensilla abundance based on feeding groups of species with and without reference to their subfamilies. Univores had the fewest of each sensillum type, and 28% fewer sensilla per antenna than the average of grasshoppers in the other feeding groups. In these latter categories, long basiconic sensilla numbers were similar and short basiconic sensilla were abundant in graminivores but few in ambivores. Slender short basiconic sensilla were fewest in the graminivores, and coeloconic sensilla were similar in all three groups. Males averaged 23% more sensilla than females. Sensilla abundance in relation to olfactory needs, diet breadth, and habitat is discussed. Desert species appear to have fewer antennal sensilla than do species in the more densely vegetated grasslands. Univores that feed on plants with high deterrence properties in either habitat have the fewest sensilla. Species in arid grasslands generally have fewer sensilla than those in damp grass-forb habitats.