The effects of aerially applied diflubenzuron on decomposition rate and litter arthropods in Prince William County, Virginia

The gypsy moth, Lymantria dispar (L.), is a serious insect pest of forest and shade trees in the United States. To minimize the effects of the gypsy moth on humans and on oak-dominated forests, government agencies and private landowners implement large-scale suppression projects. The negative consequences of broad-spectrum pesticides on non-target organisms led to their replacement with insecticides such as diflubenzuron (DFB), a chitin synthesis inhibitor. DFB was used to treat 4 million acres in the United States between 1980 and 1994. In Prince William County, Virginia, DFB was used to treat 105,715 acres from 1986 through 2000.; Prince William County provided an ideal setting for an investigation, in an operational setting, of the effects of the multiple-year use of DFB on litter decomposition rates, litter arthropod populations and DFB residues.; Three approaches were used in this study. Litter arthropod populations, leaf litter decomposition and DFB residues were compared in three study areas that represented no spray with DFB (control), and three- and five-years of spray with DFB.; Litter arthropods were collected from a total of 30 sites in the three study areas on nine sampling dates over an 8-month period. Differences in litter arthropod populations in the three study areas were assessed using analysis of variance. Leaf litter decomposition rates were determined by assessing decreases in the mass of leaves in litter bags placed at each of the 30 sites and removed at 61 days or 124 days. Differences in leaf litter decomposition rates in the three study areas were assessed using analysis of variance. Leaf litter samples from each of the 30 sites in the three study areas on each of the nine sampling dates were analyzed using high performance liquid chromatography (HPLC) to determine the presence of DFB residues.; The rate of leaf litter decomposition was greater both the three-year and five-year spray sites than in the control site. The three-year spray site had a significantly greater (P < 0.025) mean loss in leaf litter mass after 124 days. The five-year spray site had a significantly greater mean loss of leaf litter mass as compared to the control site after 61 days (P < 0.05) and after 124 days (P < 0.05).; A total of 209,065 arthropods in 27 taxa and two groups were collected from the 30 sites in the three study areas on nine sampling dates over an 8-month period. Litter arthropods were more abundant in the spray sites than in the control site in 53.7% of the comparisons made, significantly different in 17.5% of the comparisons.; Data from the litter decomposition assessment and the litter arthropod survey suggest a favorable, rather than adverse, effect of DFB treatment on litter arthropods. Litter arthropod abundance appears to be greater in gypsy moth infested areas that are treated with DFB than in gypsy moth infested areas that are not treated with DFB.; HPLC analysis of leaf litter for DFB residues produced inconsistent and inconclusive results. The HPLC method employed in this study is not appropriate for use with leaf litter and cannot be recommended at this time.