SENSILLA ON THE MAXILLARY AND LABIAL PALPS OF THE COCKROACH SUPELLA-LONGIPALPA FABRICIUS (DICTYOPTERA, BLATTELLIDAE)

Sensory structures on the maxillary and labial palps of Supella longip alpa (Dictyoptera : Blattellidae) were examined by light, scanning, an d transmission electron microscopy. Maximum variety of sensilla, inclu ding olfactory, gustatory, and mechanosensory, were found on the most distal segments of maxillary as well as labial palps. The maxillary pa lp has a long micro-furrow near the ventral edge of the medial surface of the fifth segment, which has a high population density of 73,700 s ensilla/sq. mm2. These sanilla are mostly 3-5-mum-high, 1.5-1.8-mum-th ick pegs with grooves along the hair-shaft and a slit near the distal tip. The slit and the typical arched fenestration at the tip, may allo w the dendrites to sample the external environment. This groove-and-sl it sensillum is a new sensillum described for the first time in insect s, and we designate it as GAS sensillum. Based on its morphology and a lso its sensory projections leading to the antennal lobes of the brain , as revealed by cobalt(II) uptake, the GAS sensillum appears to be ol factory. The sensillary complement on both palps is qualitatively simi lar, except for the presence of GAS sensilla on the maxillary palp. Ho wever, the quantitative estimates of the number of sensilla on both ma xillary and labial palps of females as well as males, show that both p alps have sexual dimorphism. S. longipalpa males have more chemosensil la on the maxillary palp and more taste sensilla on the labial palp th an females. Uptake of cobalt(II) by sensilla on the distal region of t he maxillary palps shows an olfactory component, projecting to the glo meruli of the antennal lobe, whereas the gustatory and mechanosensory projections of sensilla on the maxillary as well as labial palps, are mainly confined to the suboesophageal ganglion.