The Use of Laboratory Studies of Three Hymenopterous Parasites to Evaluate Their Field Potential

Abstract

Estimates of the temperature tolerances and competitive interactions of 3 introduced parasites of the spotted alfalfa aphid, Therioaphis trifolii (Monell) (= T. maculata (Buckton)), derived from laboratory investigations, are discussed relative to their distribution, abundance, and effectiveness in alfalfa fields in California. The parasites Praon exoletum (Nees), Trioxys complanatus (Quilis), and Aphelinus asychis (Walker) are solitary and endoparasitic in habit. Such factors as developmental rate, reproductive potential, and innate capacity for numerical increase calculated at various constant temperatures were considered in an effort to analyze each parasite bioclimatically. In addition, the competitive characteristics of each were considered from the standpoint of mutual interference. It was concluded that although all 3 parasite species possess certain exclusive bioclimatic features which adapt each to slightly different conditions, by and large T. Complanatus should be the most effective parasite over a wide range of climatic conditions. A scrutiny of the competitive interactions among the three did not modify this conclusion. Field studies conducted in California by other investigators have shown that although P. exoletum was prevalent shortly after the introduction of the 3 species, T. Complanatus has more recently become the most widely distributed, the most abundant, and clearly the most effective parasite. These observations suggest the value of using laboratory studies as a basis for: (1) the advanced prediction of the geographic distribution and relative effectiveness of a parasite to be introduced, and (2) examining the possibilities that several parasite species may interfere with one another in their capacities to control the pest insect.