Field Crops News

Greenbug Biological Control In Grain Sorghum and Winter Wheat

The effectiveness of naturally occurring predators and parasitoids as biological controls of greenbugs in winter wheat and grain sorghum were experimentally evaluated during 1985 and 1986 in Kansas. Three treatments or cages were used to evaluate natural enemy activity; a fine mesh (0.325 mm wide opening) cage (total exclusion), a coarse mesh (1.05 mm wide openings) cage (partial exclusion) and a large mesh (6.4 mm wide openings) cage (no exclusion). The total exclusion treatment prevented entry of all predators and parasitoids. The partial exclusion treatment prevented entry of adult lady beetles, damsel bugs, minute pirate bugs, bigeyed bugs, green and brown lacewings and large spiders. It did allow entry of small larvae or nymphs of these predators and adult parasitoids. The no exclusion cages allowed entry of all stages of the invertebrate predators and parasitoids. Greenbug populations were added to each cage (15 per plant on seedling sorghum, 25 per plant on larger sorghum and on wheat). In grain sorghum, lady beetles (Coleomegilla maculata lengi, Hippodamia convergens and Scymnus spp.) comprised 89% of the predator population. The braconid wasp Lysiphlebus testaceipes was the predominant parasitoid observed. In winter wheat, Hippodamia convergens was the predominant predator observed; no greenbug parasitoid activity was observed during the study period. The natural enemy complex consistently reduced greenbug numbers in both grain sorghum and winter wheat, based on comparing greenbug numbers in total exclusion cages with those in no exclusion cages. The greatest effect of natural enemies in both crops appeared to be from the larger predators, such as lady beetles. Parasitoids had a sporadic effect in grain sorghum and were not observed in winter wheat, possibly because of low temperatures during the wheat growing period.

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