Tarsal sensilla of Chironomus (Diptera : Chironomidae) : number, parasitogenic changes, ultrastructure, and function

Abstract

The tarsi of the middle- and hindlegs of adult Chironomus (Diptera : Chironomodae) bear short, ventral sensilla chaetica (ssc), long sensilla chaetica (Isc), and macrotrichia arising from doubly spined sockets (mss). Females of C. anthracinus, which are parasitized by mermithid nematodes, have the same numbers of ssc as normal females, but parasitized males show intersexual numbers with a high degree of feminization. In the genus Chironomus, the ssc are palmate with about 10–20 “fingers”. They are terminal pore sensilla with 4 sensory cells, unbranched dendrites, and 2 lumina in the shaft, characters indicating that they function as contact chemoreceptors. The presence of sensillum liquor may indicate an additional olfactory function. Details of dendrites, tormogen, trichogen, sheath and sensory cells are documented by transmission electron microscopy. The Ise are similar to the ssc, but lack a palmate tip and sensillum liquor. The mss are mechanoreceptors. The biological significance of the sensilla and of their parasitogenic change is discussed.