CENTRAL PROJECTIONS OF FIRST-ORDER OCELLAR INTERNEURONS IN THE BUG TRIATOMA-INFESTANS (HETEROPTERA, REDUVIIDAE)

The projections of first-order ocellar interneurons were analyzed in t he hematophagous bug Triatoma infestans by cobalt filling. The axons r un between the calyces of the mushroom bodies and dorsal of the centra l body to different regions of the brain and the subesophageal and tho racic ganglia. The interneurons can be grouped into large L cells and small S cells. The L cells have cell bodies ranging from 11.5 to 25 mu m and axons ranging from 8 to 25 mu m diameter (measured in the ocell ar nerve); the S cells have smaller cell bodies of 9 mu m or less and axon diameters less than 5 mu m. The projections of ten L cells are de scribed in detail; they project to the protocerebral posterior slope ( PS), the other ocellus (O), the optic neuropile, and the subesophageal , pro-, meso-, and metathoracic ganglia, either to ipsi- (PS I, II), o r contra- (PS IV, V), or bilateral areas. In this case projections occ ur to the same areas (PSO, PS III) or different areas at each side (PS OE; E = eye). Large-descending (LD) first-order interneurons project t o the contralateral posterior slope of the protocerebrum, the deutocer ebrum, and subesophageal, pro-, mese-, and metathoracic areas (LD I-II I). Cell bodies are located in the dorsal protocerebral lobes and pars intercerebralis, except the PS II neuron and three LD cells, which ar e located in the ipsilateral posterior protocerebrum. This is the firs t report about ocellar pathways in Hemiptera. Their adaptive function is discussed with reference to the bugs' behavior as Chagas disease ve ctors. (C) 1996 Wiley-Liss, Inc.