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

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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.

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