Species richness and fluctuation of defoliator Lepidoptera populations in Brazilian plantations of Eucalyptus grandis as affected by plant age and weather factors

Abstract

The effect of plant age and weather factors on species richness and fluctuation of defoliator Lepidoptera populations was investigated in a Eucalyptus grandis plantation subjected to a five-year survey (June 1993–July 1998) in Santa Bárbara County, State of Minas Gerais, Brazil. Adult Lepidoptera were collected every 15 days with five light traps, and the number of individuals per morphospecies in each site was recorded. Lowest numbers of individuals were obtained in July (14.4 ± 4.7 insects/trap) and highest numbers were obtained by late December (86.8 ± 41.1 insects/trap). During the five-year period, 653 species of Lepidoptera were collected and the Geometridae Stenalcidia grosica, Glena unipennaria, and Oxydia vesulia were the most abundant species. The mean seasonal fluctuation of the first two species were positively correlated with the total Lepidoptera fluctuation ( p < 0.01; r = 0.6; n = 98), unlike the third species (i.e. O. vesulia) which was poorly correlated with the total fluctuation ( p = 0.05; r = 0.2; n = 98). Multiple regression models were developed to assess the relative importance of plant age and weather factors (temperature, relative humidity, and rainfall) affecting species richness and fluctuation of Lepidoptera populations. Plant age and average temperature were the main weather factors affecting species richness and abundance of total individuals and individuals of the species S. grosica. Older plants (six- to seven-years old) and lower temperatures (≈18°C) seem to favor species richness and higher populations of Lepidoptera, especially S. grosica. In contrast, plant age and rainfall were the main factors affecting the fluctuation of G. unipennaria populations which presented higher incidence in older plants (six- to seven-years old) and higher rainfall (≈400 mm). We were unable to develop robust models for fluctuation of O. vesulia populations ( r 2 < 0.15). The obtained results suggest that high populations of the main defoliator Lepidoptera species present in the area are more likely to occur in plants older than five years and especially during the rainy season (October–March).