No abstract

Spinosad is a natural product with biological activity against a range of insects including lepidoptera. It is comprised of two major components namely spinosyns A and D. The degradation of spinosad in soil under aerobic conditions was investigated using two U.S. soils (a silt loam and a sandy loam) which were treated with either 14 C-spinosyn A or -spinosyn D at a 2X use rate of 0.4mg/kg soil for spinosyn A and 0.1mg/kg for spinosyn D. Further samples of soil were pre-sterilised prior to treatment in order to establish whether spinosyns A and D degrade abiotically. Flasks of treated soil were incubated in the dark at 25°C for up to one year after treatment. 477 478 HALE AND PORTWOOD HPLC and LC-MS of soil extracts confirmed that the major degradation product of spinosyn A was spinosyn B, resulting from demethylation on the forosamine sugar. Other dégradâtes were hydroxylation products of spinosyns A and B, with hydroxylation probably taking place on the aglycone portion of the molecule. Half lives were similar for both spinosyns and were in the range 9-17 days, with longer half lives in the pre-sterilised soils (128 -240 days) suggesting that degradation was largely microbial.