Effect of Abamectin Mixed with Mineral Oil on the Sweetpotato Whitefly (Homoptera: Aleyrodidae)

Abstract

The effects of abamectin applied alone or together with mineral (paraffinic) oil on sweetpotato whitefly, Bemisia tabaci (Gennadius), were determined on cotton plants under laboratory (leaf dip bioassays) and field conditions. Under laboratory conditions without exposure to sunlight, 1st instars were most susceptible to abamectin with a LC 50 of 0.015 mg (AI)/liter. The LC 50 for adults and 3rd instars were 0.14 and 1.83 mg (AI)/liter, respectively. The residual effect of abamectin alone or in combination with 0.5% mineral oil was estimated under controlled room conditions by exposing B. tabaci females to treated cotton seedlings at various periods after application. In other assays, effect of sunlight on the residual toxicity of abamectin was tested. The residual toxicity of 1 mg (AI)/liter abamectin applied to cotton seedlings, under laboratory conditions without exposure to sunlight, resulted in adult mortalities that declined from 86 to 39% over 28 d. A mixture of 1 mg (AI)/liter abamectin with 0.5% mineral oil resulted in higher mortalities; 100 and 88% at day 0 and 28 after application, respectively. When the seedlings were placed outdoors daily for 3 h, a low mortality of 20% was obtained 2 d after application with 1 mg (AI)/liter abamectin. A mixture of 1 mg (AI)/ liter abamectin with 0.5% mineral oil resulted in high adult mortality (93-100%) 20 d after treatment. In field trials, a mixture of 18 g (AI)/ha abamectin with 1% mineral oil decreased larval population levels throughout the experiment to a greater extent than the insecticide applied alone; resulting in 2.9 larvae per leaf at day 27 in the abamectin-oil mixture as compared with 9.6 and 14.6 larvae per leaf in the abamectin or mineral oil, respectively. Abamectin in combination with mineral oil is a potential agent for controlling B. tabaci and may be used in alternation with other effective novel compounds in insecticide resistance management strategies, especially when whiteflies and spider mites are both present in the field.