Vapor Toxicity and Concentration-Dependent Persistence of Buprofezin Applied to Cotton Foliage for Controlling the Sweetpotato Whitefly (Homoptera: Aleyrodidae)

Abstract

The biological and chemical persistence of buprofezin above and within cotton leaves, along with its vapor activity and translaminar effect against Bemisia tabaci (Gennadius) larvae, were studied. The 30% loss of foliar buprofezin varied from a short period (2.3 d) at 62.5 mg (AI)/liter to a relatively long period (13 d) at 250 mg (AI)/liter. At 250 mg (AI)/liter, complete suppression of progeny formation was observed up to 14 d after treatment; potency was reduced to 50% of its original value in 26 d for suppression of egg hatch and in 28 d for cumulative larval mortality. At least 60-70% of the buprofezin was a surface residue and was responsible for the variable persistence and for a pronounced vapor phase activity. Buprofezin vapors emitted from leaves treated with 450 mg (AI)/liter resulted in 95.7 and 62.4% kill of first instars at a distance of 2 and 4 cm, respectively. Less than 4% of the initial deposit that penetrated into the leaves was sufficient to produce a moderate translaminar effect. Treatment of the upper leaf surface with 150 and 450 mg (AI)/liter induced approximately 25% mortality of larvae placed on the lower surface. A third foliar fraction (approximately 30%), which showed high rainfastness but was readily extracted by methanol, is probably buprofezin absorbed to the leaf wax or to the inert residue of the formulation. Results strongly indicate that buprofezin acts by contact, inhalation, or both.