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

The effect of plant age and weather factors on species richness and fluctua tion of defoliator Lepidoptera populations was investigated in a Eucalyptus grandis plantation subjected to a five-year survey (June 1993-July 1998) i n Santa Barbara County, State of Minas Gerais, Brazil. Adult Lepidoptera we re collected every 15 days with five light traps, and the number of individ uals per morphospecies in each site was recorded. Lowest numbers of individ uals were obtained in July (14.3 +/- 4.7 insects/trap) and highest numbers were obtained by late December (86.8 +/- 41.1 insects/trap). During the fiv e-year period, 653 species of Lepidoptera were collected and the Geometrida e Stenalcidia grosica, Glena unipennaria, and Oxydia vesulia were the most abundant species, The mean seasonal fluctuation of the first two species we re 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 poor ly correlated with the total fluctuation (p = 0.05; r = 0.2; n = 98). Multi ple regression models were developed to assess the relative importance of p lant age and weather factors (temperature, relative humidity, and rainfall) affecting species richness and fluctuation of Lepidoptera populations. Pla nt age and average temperature were the main weather factors affecting spec ies richness and abundance of total individuals and individuals of the spec ies S. grosica. Older plants (six- to seven-years old) and lower temperatur es (approximate to 18 degrees C) seem to favor species richness and hig her populations of Lepidoptera, especially S. grosica. Tn contrast, plant age and rainfall were the main factors affecting the fluctuation of G. unipenna ria populations which presented higher incidence in older plants (six- to s even-years old) and higher rainfall (approximate to 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 mai n def oliator Lepidoptera species present in the area are more likely to occur in plants older than five years and especially during the rainy season (Octob er-March). (C) 2000 Elsevier Science B.V. All rights reserved.