ABSTRACT
The literature contains contradictions regarding the importance of puparial factors in host location by parasitoids of muscoid flies. Several olfactometers were designed to enable this matter to be resolved; the most effective design found was the "sandwich choicer," built from the tops of tissue culture plates and small petri dishes. Details are given of the sandwich choicer construction and operation, and of a simple environmental chamber suited for the olfactory testing of parasitoids. Using a Rate of Selective Attraction (ROSA) index, the parasitoids were found to be selectively attracted by volatiles from whole puparia of Musca domestica L. and Phoenicia (Lucilia) pallescens (Shannon). ROSA indexes found were: whole puparial volatiles = 5.2%/h; larval medium volatiles - 3.7%/h; 500 ppm ammonia vapor = 2.9%/h; water vapor = 2.6%/h; and the volatiles from a solvent extract of puparial cuticle = 1.7%/h. It was concluded that puparial volatiles are likely to play a role in the proximate phase of host location. The very regular rate of attraction of members of the parasitoid population is considered to reflect the operation of central nervous system "attention switching" circuitry.
