The Location of the Contact Chemoreceptors of the Stable Fly, Stomoxys calcitrans (Diptera: Muscidae)1

Two-toned, thin-walled setae on the tarsi and labella of the stable fly, Stomoxys calcitrans (L.), were identified as contact chemoreceptors by stimulation of individual setae and groups of setae, and by silver nerve stain. Location maps of tarsal contact chemoreceptors prepared for 10 flies of each sex indicated that prothoracic legs bore the most chemoreceptors and metathoracic legs the least. Contact chemoreceptors were concentrated on tarsi; a few were identified on tibiae and femora. Total numbers on opposite leg pairs were equal or nearly equal. A classification of 4 types of contact chemoreceptors was proposed on the basis of external morphology and occurrence: Type 1 (short, blunt tipped) occurred in a ventral position in the ventrolateral areas. Type 2 (with 1 flexure, acutely tipped) was found in ventrolateral areas while Type 2 (with 2 flexures, acutely tipped) occurred in dorsal and lateral areas. Type 3 (long, acutely tipped) was found only in the distal ventrolateral portions of prothoracic tarsomeres 1 through 4. Type 4 (very long, acutely tipped) occurred on all legs in the distal lateral portions of fifth tarsomeres. A comparison between the sexes in numbers of tarsal contact chemoreceptors revealed slight differences in dorsal and lateral areas except on the metathoracic legs in lateral anterior positions where the number on males was nearly 2.3 times greater. The greatest differences between sexes, however, occurred in the ventrolateral areas, which contained more than 75% of the receptors on the leg, and consisted of greater numbers of Type 2 contact chemoreceptor setae on males.