Effect of Diflubenzuron on Nontarget Canopy Arthropods in Closed, Deciduous Watersheds in a Central Appalachian Forest

Abstract

In a 6-yr study (1989-1994), we evaluated the impact of diflubenzuron on the diversity and abundance of arthropods in the Fernow Experimental Forest in West Virginia. Diflubenzuron is commonly used in gypsy moth, Lymantria dispar (L.), suppression programs in eastern forests. For the evaluation, foliage samples were taken with pole pruners from the forest canopy on 4 small deciduous watersheds; burlap bands were used on tree trunks on all watersheds. Pretreatment sampling was conducted mid-May through mid-August 1989 through 1991. Diflubenzuron was applied by helicopter to 2 watersheds; the 2 remaining watersheds served as control plots. Analysis of variance was used to compare treatment means. Gypsy moth larvae were reduced on the treated watersheds, particularly during the treatment and posttreatment year. Possible nontarget arthropod effects were researched for 27 mo after treatment. A significant reduction in the diversity of arthropod families was observed beneath burlap bands in treated plots. However, no reduction was observed for arthropod abundance. The diversity and abundance of macrolepidoptera larvae also were reduced by diflubenzuron during the treatment year. On foliage, overall arthropod family diversity and abundance, and numbers of macrolepidoptera and beetles were reduced significantly in treated watersheds. No significant reduction was seen for macrolepidoptera larval diversity on foliage. At 27 mo after treatment, total arthropod abundance and macrolepidoptera abundance on foliage remained significantly reduced. Declines were seen on treated watersheds for Carabidae, Gryllacrididae, Psocoptera, Phlaeothripidae, and some sapfeeders but were nonsignificant.