ABSTRACT
The intensive use of chemical pesticides has been a common practice among farmers which leads to increases in the abundance of pests due the disturbances caused by the mortality of natural enemies and reduction of biological controls. Aiming to evaluate the natural biological control in cotton crops on the Distrito Federal, Brazil, predators of the cotton aphid Aphis gossypii (Hemiptera: Aphididae) and parasitoids of the cotton leaf worm Alabama argillacea (Lepidoptera: Noctuidae) were identified and evaluated during 2004/2005. Evaluation was done on cotton crops located in different areas and managed with different pest-control methods (chemical insecticides, microbial insecticides and control). Five species of ladybeetles, Cycloneda sanguinea, Scymnus sp., Hippodamia convergens, Eriopis conexa and Olla v-nigrum, as well as the earwig Doru cf. luteipes and predator fly Condylostylus sp. (Dolichopodidae) and several other species of spider were observed as the most abundant predators of aphids. There was no difference in the predator species richness within the studied areas. There was a positive and significant correlation between predator species and the density of aphids in the biological insecticides treatment, suggesting a possible numerical response of predators in the absence of broad-range chemical insecticide use. Chemical pesticides offered satisfactory control only for the first generation of the cotton leaf worm A. argillacea. This finding could be related to a parasitism incidence in this treatment (2.2 ± 1.40%) against the control (23.9 ± 9.50%). A disruption effect in parasitism was not observed in the biological control area (5.8 ± 1.87%) when compared with the control. Parasitoids were found in the orders Diptera (Tachinidae, Phoridae) and Hymenoptera (Encyrtidae, Eulophidae, Chalcididae, Ichneumonidae, and Braconidae).
KEY WORDS
Cotton pests; entomofauna; parasitoids; predators; population control
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