Single females of Spalangia drosophilae Ashmead searching for 80 puparia of Hippelates collusor (Townsend), arranged in clumped or linear distributions, oviposited randomly producing equal numbers of progeny from cither host arrangement. Mixed groups of linear and clumped puparia caused changes in behavioral patterns that resulted in reduced progeny production, thus showing parasitization to be nonrandom. Host destruction was, nevertheless, greater in an all-clumped distribution, tile greater acceptance of clumped groups resulting in a greater number of progeny. Mixed groups involving a choice between linear or clumped distributions demonstrated the greater acceptance of clumped groups. Direct observation showed that the all-dumped distribution elicited the greatest overall initial attraction for hosts and subsequent movement to other areas. It was concluded that maximum host destruction resulted when completely random behavior was involved. A recognition of this, however, required a knowledge of behavior, host condition, and progeny production. The question of evaluating an exotic parasite’s effectiveness before introduction is discussed.

Betulaphis viridis is described and illustrated. It is a bright green species that occurs on the upper surfaces of the leaves of Betula pendula Roth and is known only from Ontario.