Effects of environmental heterogeneity on Lepidoptera and Hymenoptera populations in Eucalyptus plantations in Brazil

For 5 months, insects from the Lepidoptera and Hymenoptera orders were collected at five sites: in the interior of a Brazilian native forest, in the zone of contact between the native forest and a Eucalyptus plantation, and in three sites within the Eucalyptus plantation, at 200, 400 and 600 m from the edge of the native forest. Lepidoptera were collected with light traps and divided into three groups in relation to the damage they cause to Eucalyptus: primary pests, secondary pests, and other abundant but non-pest species. Hymenoptera were collected with Malaise traps and categorized as predators, egg parasitoids or larval parasitoids, In general, the heterogeneity hypothesis was supported: total lepidopteran abundance was higher and total natural enemy abundance was lower in the Eucalyptus plantation than within the native forest or at the edge of the native forest and the Eucalyptus plantation. Negative correlations were found between the abundance of Lepidoptera and that of egg parasitoids and larval parasitoids. No significant differences in the abundance of lepidopteran pests and hymenopteran natural enemies were found among the three sites within the Eucalyptus plantation. Plantations of Eucalyptus intercalated with native vegetation could reduce outbreaks of lepidopteran pests by increasing numbers of Hymenoptera natural enemies of these pests. (C) 1998 Elsevier Science B.V.