Head morphology of 1st and 5th instar nymphs of Triatoma circummaculata and Triatoma rubrovaria (Hemiptera, Reduviidae)

Morphological structures of the head of 1st and 5th instar nymphs of Triato ma circummaculata and Triatoma rubrovaria were revealed by analysis using s canning electron microscopy (SEM). Differences between Ist and 5th instar n ymphs of these two species were observed in the postocular callosity, the n umber of ommatidia and tapered hair, the small segment between antennal seg ments, the rostrum third segment and slit lines. These slit lines were diff erent only in the 5th instar. Similarities observed were the presence of ta pered hairs in the joints, and the type of sensilla in the antennal segment s. Only the Ist instar shows anteclypeus and gena sensilla. The antennal se gments comprise the following types of sensilla: basiconica, bristles type I, bristles type II, bristles type III, campaniformia, coeloconica, chemose nsilla, placodea, trichobothria and trichoidea. We describe here for the fi rst time six (3+3) sensilla basiconica on the dorsal portion of the first s egment of the rostrum. (C) 2000 Elsevier Science Ltd. All rights reserved.