Some factors influencing the efficiency of Apanteles medicaginis Muesebeck (Hymenoptera: Braconidae) as a parasite of the alfalfa caterpillar, Colias philodice eurytheme Boisduval

Abstract

Investigations were conducted to determine important factors influencing the efficiency of A. medicaginis as a parasite of the alfalfa caterpillar C. philodice eurytheme. Studies of the rate of development of Colias at various temperatures indicate that it becomes of economic importance only during periods of high temp., for at low temps. the development time exceeds the time between cuttings of alfalfa. It is in high-temp. areas that A. medicaginis becomes an important factor in the control of C. p. eurytheme. Apanteles requires a much shorter time for development than does Colias, and should be able to respond rapidly to changes in host density: however, because alfalfa is cut every 30 to 35 days, it is difficult for the parasite to complete 2 generations between cuttings. This difference in emergence time, coupled with the difference in flight characteristics and host habitat selection, results in concentration of host and parasite in different fields so that at times small numbers of Apanteles females must cope with very large numbers of Colias. At such times the efficiency of A. medicaginis seems to be restricted by its limited longevity and associated low reproductive capacity. Neither superparasitism nor hyperparasitism seem to be important limiting factors. || ABSTRACT AUTHORS: Authors