RESPONSE OF SOIL AND LEAF-LITTER MICROARTHROPODS TO FOREST APPLICATION OF DIFLUBENZURON

The objective of this study was to assess the effects of forest applic ation of diflubenzuron (Dimilin(R)), a gypsy moth suppressant, on nont arget invertebrates in litter and soil on the forest floor. Four exper imental watersheds (two treatment and two reference) in the Fernow Exp erimental Forest, West Virginia, were sampled for two years before and one year after application of diflubenzuron (70 g ha(-1), Al). Soil a nd leaf litter arthropods were monitored before and after application using soil cores and litter bag colonization samplers. Frequency analy sis, BACIP, and ANOVA were used to analyse the data for diflubenzuron treatment effects. During the 36 month study, soil core samples were d ominated by mites (49%) and springtails (28%). A total of 19 taxonomic groups were suitable for statistical analysis. We detected no signifi cant treatment effects based on total organism counts or counts by tro phic categories (p < 0.05). There were no significant treatment effect s for populations of major taxonomic groups, except for Araneae (spide rs). Analysis of leaf litter bags also showed no significant differenc es in total numbers of invertebrates or in trophic categories between treated and reference watersheds during the 12 month post-treatment st udy. Density of one species of springtail (Sminthurus purpurescens) an d springtails as a group were significantly lower in treated watershed s. High variation was associated with both soil core and leaf bag samp les; because of this variation, a significance level of 0.05 should be considered very conservative. Long-term trends in soil biota were evi dent, demonstrating the need for well-established pre-treatment baseli ne data for pesticide impacts on soil organisms.