Sexual dimorphism of tarsal receptors and sensory equipment of the ovipositor in the European corn borer, Ostrinia nubilalis.

Sensilla on legs and ovipositor of the moth Ostrinia nubilalis were investigated by light and scanning electron microscopy. The ovipositor is composed of two papillae densely packed with medium length mechanoreceptor sensilla (MRb: 80-160 microns, n = 420-460). Long mechanoreceptor sensilla (MRa: 250-300 microns, n = 20-24) and contact chemoreceptors (CRa: 30-40 microns, n = 20-28) are evenly distributed at the periphery of these papillae. Legs support contact chemoreceptors (CRa), scattered among the scales. The pretarsus structure of each leg includes a single contact chemoreceptor (125 microns) inserted dorsally. The fifth tarsomere bears a ventral area without scales on which contact chemoreceptors are disposed in two parallel rows (CRb: 40-60 microns). A sexual dimorphism was found in the number and density of these sensilla (females: mean = 5.3, SD = 1.0; males: mean = 3.3, SD = 0.7), and in the size of the sensory field. The possible involvement of these sensory structures in oviposition site selection is discussed.