Biological activity of the spinosyns, new fermentation derived insect control agents, on tobacco budworm (Lepidoptera : Noctuidae) larvae

The spinosyns are a new class of fermentation-derived tetracyclic-macrolide insect control agents that are active against lepidopterous pests such as the tobacco budworm, Heliothis virescens (F.). Nine spinosyns, 2 pesudoagly cones (each lacking 1 of the sugar moieties), and the aglycone (lacking bot h sugar moieties) were tested on neonate a virescens larvae in a drench ass ay. Spinosyn A, the principle component of spinosad (Tracer Naturalyte Inse ct 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 labor atory efficacy assays. Although spinosyn A (LD50 = 1.28, 2.25 mu g/g) was s ignificantly less active than cypermethrin (LD50 = 0.52 mu g/g) in topical bioassays against 3rd-instar a 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 a virescens larvae with T(50)s (time to 50% knockd own) at 10 mu g per larva of 81 min and 25 min, respectively. Spinosyn A wa s significantly less active than cypermethrin in a dried residue contact bi oassay, but equivalent (no significant differences) in activity to cypermet hrin in diet/egg and leaf-spray bioassays, and significantly more active th an cypermethrin in a leaf-dip bioassay. Thus, spinosyn A demonstrates that natural products can provide efficacy against pest lepidopterous larvae, su ch as H. virescens, that is on par with that observed for some of the most active synthetic insect control agents, including many pyrethroids.