Diazinon Resistance in Different Selected Strains of Chilo suppressalis (Lepidoptera: Crambidae) in Northern Iran

Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is a cosmopolitan and destructive pest in rice fields of the world. This pest was reported in 1973 in Iran, and it has since spread widely in rice, Oryza saliva L., fields throughout the country. In this study, we tried to evaluate comparative toxicity of diazinon in five colonies of C. suppressalis, collected from Babol (Ba), Amol (Am) of Mazandaran Province and Rasht (Ra), Sheikhmahale (Sh), and Gourabzarmikh (Go) of Guilan Province, northern Iran. The LD50 values were compared. We also evaluated the general esterases, alkaline phosphatase (ALP), glutathione transferase (GST), and acetylcholinesterase (ACNE) activities from the five populations. The LD50 values of Ra, Ba, Am, and Sh (12.64, 11.4, 7.17, and 3.71 mu g/mg larva(-1)) were 13.67-, 12.33-, 7.75-, and 4.02-fold higher than Go population (0.924 mu g/mg larva(-1)). Using a-naphthyl acetate as substrate, the general esterase activities in Ra, Ba, Am, and Sh colonies were, respectively, 1.81-, 1.68-, 1.75-, and 1.35-fold more than those in Go Population. When beta-naphthyl acetate was used as the substrate, activity ratio wits measured 1.98-, 2.58-, 1.25-, and 1.24-fold compared with the Go population. Glutathione transferase activities in Ra, Ba, Am, and Sh populations were 1.27-, 1.68-, 0.98-, and 1.7-fold more than those in Go, when 1-chloro-2,4-dinitro-benzene was used as the substrate. When 1,2-dichloro-4-nitro-benzene was used as the substrate, activity ratio was measured 1.14-, 1.42- 0.56-, and 0.95-fold compared with Go population. The ALP activity demonstrated a significant difference among these populations and in Ra, Ba, Am, and Sh larvae were 3.54-, 4.62- 3.84-, and 2.18-fold more than Go. The ACNE inhibition or I-50 value wits 0.19, 0.22, 0.31, 0.19, and 0.26 mM in Ra, Ba, Am, Sh and Go populations, respectively. However, the results showed no significant differences in studied colonies. These biochemical characterizations of general esterases ALP, GST, and ACNE were consistent with diazinon bioassay in the five populations. It is inferred from increased esterase alkaline phosphatase and glutathione transferase, activities that might play an important role in the increasing resistance in C. suppressalis to diazinon among these five populations.