Effects of Host Plant Cultivar and Insecticide Type on Rice Damage and Growth of Chilo suppressalis (Lepidoptera: Crambidae) Larvae in Semi-field Conditions

Rice striped stem borer, Chilo suppressalis (Walker, 1863), is considered as a major destructive pest in paddy fields in the most regions of Iran. In this study, the impact of the rice cultivars, Tarom and Shiroudi, and the insecticides, cypermethrin, tebufenozide and the emulsion and granule formulations of diazinon were examined on the damage indices, percentages of dead heart and whitehead. The study was performed as factorial randomized complete block design using artificial infestation in semi-field conditions in Amol County. No significant interaction was found between rice cultivar and insecticide for all indices in both vegetative and reproductive stages (P>0.05). The results of main effects in both phenological stages indicated that the weight of live larvae and damage indices were significantly higher on Tarom than those of Shiroudi (P & LE;0.05), while no significant difference was detected in larval mortality on the cultivars (P>0.05). The main effects of insecticide were significant for all biological and damage indices (P & LE;0.05). The efficacies of tebufenozide and cypermethrin in terms of larval mortality were 47.57 and 74.90 % at vegetative stage reaching to 79.15 and 92.08% at reproductive stage, respectively. The lowest efficacy in terms of larval mortality (73.33%) was obtained on plants treated by diazinon emulsion. At reproductive, the survived larvae weighed 170.80 mg.seedling-1 and the corrected whitehead index compared to the control reached 50.04% on plants treated by diazinon emulsion. According to the results, tebufenozide, regarding its relatively high efficacy and environmental compatibility, is suggested to be assessed further for integrated C. suppressalis management in the field conditions.