Joint action of benzoylphenylureas in binary mixtures against larvae of the cotton leafworm,Spodoptera littoralis

Abstract

In preliminary laboratory tests, the joint activity of six benzoylphenylureas (BPUs) was studied by investigating the activity of 90 of their binary mixtures against fourth-instar larvae of the cotton leafworm,Spodoptera littoralis (Boisd.), fed for 72 h on 10 ppm BPU-treated castor bean leaves. Experimental mixing ratios were 1:1, 1:4, and 1:9. At 10 ppm, the activity of the six BPUs was divided into two distinct groups. The first included the more active compounds (XRD-473, GR-333, and chlorfluazuron) while the second was composed of the relatively less active ones (diflubenzuron, triflumuron, and Dowco-439). Results of the assays indicated that only 18 of the 90 tested binary mixtures showed potentiation, whereas the majority, 70 mixtures, exhibited additive effects; two interacted antagonistically. Most of the potentiated pairs were at a mixing ratio of 1:9, pairing one strong BPU (at the low ratio) with a weak one (at the high ratio). The mixing ratio of 1:1 resulted in additive effects.