LIMITS OF VOLATILE CHEMICAL DETECTION OF A PARASITOID WASP, Microplitis croceipes, AND AN ELECTRONIC NOSE: A COMPARATIVE STUDY

Volatile chemical signals are used by many animals to find food, mates, or hosts. While the keen sense of smellof dogs has been used for centuries, other animals have not been significantly utilized. Recent studies have indicated that manyinsect species have the ability to learn volatile chemical compounds in association with food or other resources. These insectspresent a novel approach to volatile chemical detection that could provide a highly sensitive, inexpensive, flexible, and portablesensor. One characteristic of insects that makes them desirable as a potential chemical detector is their ability to detectextremely low levels of chemical compounds. A parasitoid wasp, Microplitis croceipes, was used as the model insect fordetermining the threshold of response for four compounds: 3-octanone, a compound found in many fungal pathogens;myrcene, a volatile constituent released by cotton plants fed on by cotton bollworms; and putriscene and cadaverine, twoproducts of the breakdown of dead animal protein by microorganisms. Eighteen wasps were trained to each of these individualcompounds at one dosage and tested at decreasing dosage levels until their responses were negligible. Each dosage was testedwith 18 freshly trained wasps. The wasp response to the odor was determined by a searching behavior called antennating.Wasp response was measured by the length of time the wasp antennated when exposed to the odor. The mean wasp responsefell below 10 s at approximately 3.1 10-7, 2.9 10-7, 3.9 10-6, and 4.5 10-7 mol L-1 of compound for 3-octanone,myrcene, cadaverine, and putriscene, respectively. For comparative purposes, the detection limits of an electronic nose, theCyranose 320, was determined for two of the four compounds. The response limits of the wasp for the compounds 3-octanoneand myrcene were 74 and 94 times better than the electronic nose, respectively. The response limit of the wasps to putriscene,3-octanone, and myrcene was approximately 10 times better than to cadaverine.