BIOLOGICAL AND ECOLOGICAL STUDIES OF SELECTED NATURAL ENEMIES OF GEOCORIS SPP. (HEMIPTERA: LYGAEIDAE) IN SOUTHERN ARIZONA ALFALFA FIELDS.

Abstract

Field studies of population of Geocoris and Nabis indicated that the density of adult Nabis was higher than Geocoris before April, but the reverse was true after April. In general, the abundance of adults and nymphs of each species was caused by alfalfa harvesting, dispersal of adults, discrepancies of sweep-net sampling, differences in mortality of eggs and the differences in the diapause termination of adults. The field cuttings of alfalfa reduced populations of both species, but adults were reduced more than the nymphs. In laboratory studies adults and nymphs of each species fed on each other on alfalfa in small cages, but in larger cages when only adults were caged, interspecific predation of adults did not occur. This suggests that, in the field, interspecific predation of nymphs can be more prevalent than adults of each species since nymphs which are more sedentary than adults are less affected by alfalfa cuttings. A number of predatory insects other than Nabis that were common in the alfalfa, such as Chrysopa carnea Stephens, Orius tristicolor (White), Hippodamia convergens Guerin, and Sinea confusa Caudell, were also found to prey upon Geocoris in the laboratory. Hyalomya aldrichii Townsend was the only parasite reared from Geocoris adults and nymphs from the field. The parasite did not numerically respond to the density of Geocoris and had minor impact on the population of the predator. The host preference of this parasite among the Geocoris spp. and between Geocoris and Nabis was not determined since rearing the parasite in the laboratory failed. Telenomus sp. parasitized groups of Geocoris eggs exposed in alfalfa fields. In the laboratory, it parasitized both G. pallens and G. punctipes eggs. Rearing the parasite at 30(DEGREES)C resulted in poorer emergence of adults than at 20(DEGREES)C and 25(DEGREES)C. Predaceous insects that synchronize with populations of Geocoris, larger in size then Geocoris, especially Nabis and Sinea spp. may be more important than parasites in regulating population of Geocoris in the field.