Some natural factors limiting the abundance of the alfalfa butterfly

Abstract

does not appear. First page follows. Introduction The early history of the alfalfa butterfly as a pest is well covered in the works of (Wildermuth (1911), (1914), (1920).4 In California and other parts of the West the caterpillar of this butterfly, Colias eurytheme Boisduval,5 is the most serious pest attacking alfalfa. Here, in cases of severe outbreaks, entire fields are often defoliated. During the course of the alfalfa weevil investigation in the region adjacent to the San Francisco Bay and in the northwest portion of the San Joaquin Valley, it was observed that the amount of damage done by the alfalfa butterfly varied not only from year to year but from field to field. One of the reasons for this behavior came to light during September, 1938. In an alfalfa field near Tracy a large number of larvae were collected for use in toxicity studies. The alfalfa was about one third grown and supported a very large population of small larvae. At first it appeared that the developing population was sufficient to inflict serious damage. However, most of the larvae collected proved to be parasitized by a hymenopterous parasite, Apanteles flaviconehae Riley. (Wildermuth (1914)) probably referred to this parasite when he recorded A. fiavicombe as a relatively unimportant parasite of the alfalfa butterfly at Salt Lake City, Utah.