Antennal sensilla in adult Helicoverpa assulta (Lepidoptera: Noctuidae): morphology, distribution, and ultrastructure

This study was done to elucidate structure and distribution of antenna and antennal sensilla in adult oriental tobacco budworm, Helicoverpa assulta (Guenee). The antenna consisted of scape, pedicel, and flagellum. The flagellum of both sexes had 6 major types of sensilla. The number of flagellar subsegments differed slightly between the 2 sexes. Sexual dimorphism was also noticed in the total number of sensilla and in the subtypes of sensilla trichodea. Sensilla chaetica were mechanical and contact chemoreceptors. All sensilla trichodea were thick-walled, multiporous sensilla with pitted surface characteristics typical of olfactory sensilla, and had 2-5 unbranched dendrites. These sensilla were further divided into different subtypes, which were not the same between the sexes. Subtypes I and II were divided by scanning electron microscopy, and subtypes A and B, which existed only in the male and may be pheromone-sensitive sensilla, by transmission electron microscopy. Sensilla basiconica were thin-walled, grooved, multiporous sensilla and had >10 dendritic branches. Sensilla auricillica were thin-walled, grooved, multiporous sensilla, flatter than sensilla basiconica and had >30 dendritic branches. Sensilla coeloconica were double-walled, grooved, multiporous sensilla and had spoked channels instead of pore tubules. The last subsegment of flagellum had 2-3 sensilla styloconica. Also, most of sensilla styloconica were distributed uniformly in the upper-middle region of each flagellar subsegment and another sensillum styloconicum was distributed randomly in each flagellar subsegment. The pedicel had 2 groups of Boehm bristles, sensilla basiconica, and the Johnston organ. The scape had 2 types of scales, 2 groups of Boehm bristles, and the scape muscles attached to cuticle of the pedicel. The antennal socket also had 2 groups of Boehm bristles.