No abstract

The interrelationships between the pea aphid, Acyrthosiphon pisum (Harris) and its parasite, Aphidius smithi Sharma & Subba Rao, were studied i' _l alfalfa fields at ~ive: side, California from July 1961 to July 1962 and at Pala Mesa (San Diego County), Cahforma from July 1962 to July 1963.Response of Aphidius to changes in Acyrthosiphon density was repeatedly observed in each plot. However, in both areas during much of the year the wasps' density dependence _was obscured by certain factors in the environment. Weather conditions, agricultural practices, and competition from fungus disease appeared to be the most important of these factors. In each area, though, in late spring when conditions were apparently optimum for parasite activity the wasp evinced a clear cut response to increasing aphid density and quickly overwhelmed the host population.The possible relationships of the findings of the present study to the density-dependent phenomenon in general are briefly discussed.

The interrelationship between the aphid, Acyrthosiphon pisum (Harris) and its parasite, Aphidius smithi Sharma & Shubba Rao, was studied in two strip harvested alfalfa fields near Famoso, California in the summer of 1963. Strip harvesting had a stabilizing effect on the alfalfa environment particularly as regards micro climate. As a result both Acyrthosiphon and Aphidius remained highly active in midsummer. By contrast in previously studied solid harvested alfalfa fields both species were strongly depressed during summertime. The current studies also produced information on migration of female Aphidius and on the wasp's density dependence.

No abstract

No abstract