External morphology of antennal sensilla of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae)

External morphology of antennal sensilla on female and male Trichogramma australicum (Hymenoptera: Trichogrammatidae) was examined using scanning electron microscopy. Antennae show strong sexual dimorphism in structure and types of sensilla. The female antenna displays 14 types of sensilla: basiconic capitate peg sensilla (types 1 and 2), campaniform sensilla, chaetica sensilla (types 1-3), coeloconic sensilla, falcate sensilla, placoid sensilla (types 1 and 2), styloconic sensilla and trichoid sensilla (types 1-3). The male antenna displays 12 types of sensilla: basiconic capitate peg sensilla (type 2), campaniform sensilla, chaetica sensilla (types 1-5), coeloconic sensilla, placoid sensilla (type 1), and trichoid sensilla (types 3-5). Falcate and styloconic sensilla occur only on the female antenna. Both sensilla probably are associated with host examination, host discrimination and oviposition behaviour. Male antennal trichoid sensilla types 4 and 5 are probably associated with courtship behaviour, because these types occur only on the male. We propose the term "falcate sensilla" for a unique female antennal sensilla; the number of falcate sensilla may be used for identification of Trichogramma spp. In addition, we report the presence of placoid sensilla type 2 and difference in structure of coeloconic sensilla in T. australicum. Variation in structure and position of antennal sensilla are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.