Abstract
Enemy removal experiments and enemy trap experiments were used for evaluating the natural enemies of greenbug, S. graminum (Rondani). In enemy removal experiments, malathion applied at 0.03 kg Al/ha and chlorpyrifos applied at 0.005 kg Al/ha produced no significant differences (at P = 0.05) in the natural enemy or greenbug populations when compared with the untreated (control) plots. In a similar comparison, three application frequencies of these insecticides, i.e., three, seven and fifteen day intervals, produced no differences in the greenbug or natural enemy populations. In enemy trap experiments, Karate (0.02 kg Al/ha) and Bidrin (14.88 oz/ha) applications at three day intervals were effective to exclude predators. These natural enemy exclusion agents permitted significantly higher populations of greenbugs and lower populations of predators in the treated plots when compared with the untreated plots (P = 0.05). The relative usefulness of the two approaches is discussed in evaluating the natural enemies of greenbug. Results from experiments on the effects of malathion on host selection behavior present some interesting contrasts to earlier work on effects of insecticides on beneficial insects. Aphelinus asychiv (Walker) in an olfactometer was attracted to malathion-treated sorghum leaf infested with greenbug. This suggests that the insecticide or associated additives produced resulted in an increased attractiveness to the pest-insect-plant complex. The parasites preexposed to malathion displayed sluggish or no movement when presented with greenbug-infested and uninfested sorghum leaves in an olfactometer. These results suggest that failure of parasite exclusion in the treated plots may be primarily due to parasites accumulating in the treated plots due to their attraction to malathion, and to their inability to move after contacting the malathion.
Rao, Asha (1996). Evaluation of natural enemies of greenbug, Schizaphis graminum (Rondani), on sorghum using two approaches of the insecticidal check method. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -R368.