Biological Activity of the Spinosyns, New Fermentation Derived Insect Control Agents, on Tobacco Budworm (Lepidoptera: Noctuidae) Larvae

Abstract

The spinosyns are a new class of fermentation-derived tetracyclic-macrolide insect control agents that are active against lepidopterous pests such as the tobacco bud worm, Heliothis virescens(F.). Nine spinosyns, 2 pesudoaglycones (each lacking 1 of the sugar moieties), and the aglycone (lacking both sugar moieties) were tested on neonate H. virescens larvae in a drench assay. Spinosyn A, the principle component of spinosad (Tracer Naturalyte Insect Control), was the most active of the spinosyns examined (spinosyn A LC₅₀ = 0.3 ppm) and was as active as cypermethrin (LC₅₀ = 0.26 ppm). Spinosyn A was also tested directly against cypermethrin in a further series of laboratory efficacy assays. Although spinosyn A (LD₅₀ = 1.28,2.25 mg/g) was significantly less active than cypermethrin (LD₅₀ = 0.52 mg/g) in topical bioassays against 3rd-instar H. virescens, the results show spinosyn A to be in the activity range of some pyrethoids and more active than a variety of other insect control agents. Spinosyn A and cypermethrin exhibited a rapid knockdown of 3rd instar H. viescens larvae with T₅₀s (time to 50% knockdown) at 10 mg per larva of 81 min and 25 min, respectively. Spinosyn A was significantly less active than cypermethrin in a dried residue contact bioassay, but equivalent (no significant differences) in activity to cypermethrin in diet/egg and leaf-spray bioassays, and significantly more active than cypermethrin in a leaf-dip bioassay. Thus, spinosyn A demonstrates that natural products can provide efficacy against pest lepidopterous larvae, such as H.. virescens, that is on par with that observed for some of the most active synthetic insect control agents, including many pyrethroids.