Resistance Monitoring And Studies On Biochemical Mechanisms Of Bemisia Tabaci(Gennadius)to Spinosad And Abamectin

Bemisia tabaci (Gennadius) is an invasive pest in the world and causes severe economic losses to the agricultural production in China. Two of the most prevalent cryptic species are B. tabaci Middle East-Asia Minor1(MEAM1) and Mediterranean (MED). They are invasive cryptic species and often occur in some areas in China. The MED particularly has strong resistance to some insecticides and more difficult to be controlled. In recent years, because of the heavy use of Synthetic insecticides, the resistant problem of B. tabaci becomes increasingly serious. Many conventional insecticides including organophosphates and carbamates have made B. tabaci develop high resistance. In some areas, B. tabaci has also developed resistance to insect growth regulators and neonicotinoid insecticides. The extensive resistance monitoring is in urgent need. We should select the insecticides of high efficiency, low toxicity and safty to control B. tabaci. We studied the discrimination of two invasive cryptic species of B. tabaci by using TaqMan allele-selective PCR, resistance monitoring to spinosad and abamectin, and the biochemical mechanism of resistance of B. tabaci. It is meaningful to the intergrated pest management and resistance control on B. tabaci. The results are summarized as follows:1. TaqMan allele-selective PCR was used for high-throughput allelic discrimination of MEAM1and MED in this study. A single nucleotide polymorphism (SNP) in a conservative region of the mitochondrial COI gene was selected as the amplification target. The TaqMan-MGB fluorescent dye-labeled was used in real-time quantitative PCR. Fourteen populations of B. tabaci collected from Beijing were identified with the method. The results showed that all samples of B. tabaci were cluster with the known MED species as shown by the higher fluorescence of FAM dye in scatter plot analysis of fluorescence data, and so the Beijing populations examined were all B. tabaci MED.2. We assayed bioactivity of spinosad and abamectin on different development stages of B. tabaci. The results showed that there was no apparent toxicity on eggs of B. tabaci. Compared to different concentrations of reagents and control treantment, eggs hatchability of MED species were between94%and97%. Eggs hatchability of MEAM1species were91%and93%. There was higher biological activity on nymphs and adults, and the adult stage is the best prevention. They were excellent insecticides to control B. tabaci. Abamectin had stronger bioactivity on nymphs and adults of B. tabaci. The lowest of LC50of nymphs was0.26mg/L and the minimum of LC50of adults was0.03mg/L. B. tabaci was more sensitive to abamectin than spinosad.3. Based on the toxicity of spinosad and abamectin to B. tabaci, the activities of detoxifying enzymes were studied at lethal concentration. The results showed that spinosad and abamectin could induce insect detoxifying enzymes system to stress reaction. Carboxylesterase, acetylcholinesterase and glutathione S-transferase were effective in the resistance of B. tabaci to spinosad and abamectin. Spinosad had obvious activation to carboxylesterase in B. tabaci. The activity of carboxylesterase after feeding for8h was significantly higher than CK (P＜0.01). The activity was the highest at48h after treatment and it reached14.49U/mg prot. Abamectin had inhibition after activation to carboxylesterase and glutathione S-transferase in B. tabaci. Spinosad on the activity of acetylcholinesterase was similar to abamectin. They were characterized by inhibition, activation and then inhibition.