Toxicities And Effects On Biochemical Properties Of Spinosad To Beet Armyworm (Spodoptera Exigua Hǖbner)

Spinosad is the first member of the Naturalyte class of insecticides developed by Dow Agrosciences. It is secondary metabolites produced by Saccharopolyspora spinosa under natural fermentation conditions. Spinosad has a unique chemistry and mode of action, a high level of activity against economically important pests, a short half-life, and large margins of safety for mammals, birds, fish and even most beneficial insects. Few electrophysiology studies showed that the mode of action of spinosad is twofold: the nicotinic acetylcholine receptor and the GABA receptor are both affected. Toxicities and effects on biochemical properties of spinosad to beet armyworm were reported in this paper. It is our hope that this research will assist the others in studing the mode of action of spinosad, and assist pest managers in using the compound to control pests, thereby perserving its efficacy. Additionally, we hope this information will serve for the resistant management of beet armyworm.The main results are listed as follows:1. Spinosad has a high level of toxicity comparable to that of some of today's most active insecticides against third instar beet armyworms through exposure of larvae to dipped cabbage leaves. The LCso value of third instar larvae is only 0.80 mg spinosed/L. The synergists, PBO and TPP and the Bacillus thuringiensis failed to synergize spinosad in the population.2. Spinosad did not affect egg hatching, but cause substantial mortality of newly-hatched larvae; Susceptibilities to spinosad of different instar larvae of beet armywom were determined through exposure to dipped cabbage leaves. The LCso value of the second instar larvae was 0.09 mg/L. but the third and forth instar larvae were 0.80,1.42mg/L respectively, the activities of spinosad were decrease 8.89, 15.78 times; Spinosad did not affect adut emergence, pupal weight of beet armyworm, but affected pupating rate; The adult egg-production, life-span were significantly decreased when the adult treated with spinosad.3. When the third instar larvae were fed with leaves treated with spinosad at 0.1, 0.25, 0.8mg/L, the respiratory rate and maintain time increased along with dose increasing.4. Result in vitro showed that the activity of polyphenlo oxidase (PPO) in beet armyworm 4th intar larvae was significantly decreased, but the activity of carboxylester ase(CarE) in beet armyworm 3rd instar larvae was not influenced. Result in vivo showed that the activity of PPO was significantly increased firstly, but after 24h it was significantly decreased when the 4th instar larvae was fed with leaves treated with spinosad (0.1,0.25,0.8mg/L). The CarE activity was significantly increased 1.61 times when the 3rd instar larvae treated with spinosad at 0.05mg/L. The esterase isoenzymes polyacrylamide gel electrophoresis(PAGE) also showed the changes of the CarE activities.5. The endogenous enzymes of protective system including peroxide dismutase(SOD), peroxidase(POD) and catalase(CAT) were found to exist in the larvae of beet armyworm. When the 3rd instar larvae treated with spinosad at 0.05mg/L. The SOD activity was increased at 4h and the POD activity was increased at 4h and 12h , But the other time the three enzyme activities had no changes. The results showed that the activity of spinosad was not closely correlated with the protective enzyme systems.