Effects of fenvalerate, a synthetic pyrethroid insecticide, on nontarget organisms in an old-field ecosystem

Fenvalerate Pydrin('(REGTM)), cyano(3-phenoxybenzyl)-methyl 4-chloro-(alpha)-(1-methylethyl)benzeneacetate, a synthetic pyrethroid insecticide, was experimentally applied to 3 of 6 1-ha study plots on an old-field site. Two applications of 0.112 kg AI/ha (0.1 lbs/acre) were made during both 1980 and 1981. The effects of fenvalerate on arthropod and small mammal communities, and the degradation and movement of residues are reported;Arthropod populations were monitored with pitfall traps and sweep nets. No significant treatment differences were detected among ground arthropods. Most foliar arthropod populations were significantly reduced (P < 0.05) by fenvalerate, with varying degrees of population recovery, ranging from increases above control levels within 3 weeks by thrips (Thysanoptera) to essentially no recovery by beetle larvae. A few foliar arthropod groups were not reduced, but only springtails (Collembola) significantly increased in number after application;Nine small mammal species were captured in live traps during both years from grids in each plot. In 1980, 16,632 trap nights resulted in 1638 captures of 390 individuals, and in 1981, 14,700 trap nights produced 3911 captures of 787 individuals. Insecticide applications did not significantly affect population size, reproduction, age and sex ratios, or movement patterns for any species;The highest fenvalerate residues were detected on vegetation (12.1 ppm), with little evidence of drift into control plots. Residue concentrations declined exponentially with half-lives ranging from 5.9 to 10.6 days. All insect samples contained < 0.5 ppm fenvalerate. These residues also declined through time. The highest residue levels were found in short-horned grasshoppers ((LESSTHEQ) 0.33 ppm). Residues in ground beetles (Carabidae) were < 0.15 ppm. All mammalian samples contained (LESSTHEQ) 1.0 ppm, with the meadow voles (Microtus pennsylvanicus) containing higher residues than deermice (Peromyscus maniculatus). The low residue levels reflected the low application rate, rapid environmental degradation, and rapid mammalian metabolism of fenvalerate.