Some Effects of Temperature and Competition on the Distribution and Relative Abundance of Aphytis Lingnanensis and A. Chrysomphali (Hymenoptera: Aphelinidae)

Abstract

For the past 10 years 2 insect parasites, Aphytis linyn(ncnsis Compere and A. chrysomiphali (Mercet), have existed in southern California in necjarly identical ecological niches. These 2 species aie ci(,se.y related ectoparasites of the California red scale, ,uonidiella aitrantii (Mask.), one of the most troul)lesome citrus tree pests. This scale species constitutes the only suitable host available to eithk.r parasite in the areas of this study. Both par asites attack the same stages of the host and have very similar life histories and habits. I ndiv idul1.s of the 2 l)arasite species live in the same manner, in the same type of environment, and on identical food, both as larvae and as adults. At low magnification they are readily distinguishable only in the pupal stage; at higher magnification adults can he distinguished by an expert. Aphytis chnvsouiiphlli has heen present in California for ahout 60 years, p)resumahly having been accidentally introduced, directly or indirectly, from the Mediterranean area. It became generally distributed as a parasite of the California red scale in southern California many years ago, hut was much more common in some areas than in others. A pali ntis linynanesis a purposeful introduction from the Orient, was colonized throughout southern California h)y the l)epartment of Biological Control, Citrus lFxperiment Station, Riverside, heginnlling in 1948 in an effort to obtain better l)iological control of the California red scale. Fromn that time to the present these species have been in direct competition wherever they coexist. After colonizing Aphytis lingnanensis in 21 field llots in which A. chrysoniphali already existed, it was found that linynanensis usually became dlominant, sometimes to the point of apparent extermination of chrysonziphali, in a period of from 1 to 4 years (approximately 10 to 40 parasite gen' Paper No. 1181, University of California Citrus Experimellt Station, Riverside, California. 2 Entomologist, Department of Biological Control, University of California Citrus Experiment Station, Riverside. 3 Assistant Entomologist, Biological Institute, Belgrade, Yugoslavia. Research performed as an International Cooperation Administration Fellow at the University of California Citrus Experiment Station, Riverside. erations) (DeBach 1954). To quote from the same paper: