Efficacy of some insecticides on larvae and adults of alfalfa weevil, Hypera postica in field conditions

Alfalfa weevil, Hypera postica Gyllenhal is the most important pest of alfalfa fields in Iran. Main damage is related to larvae by feeding on plant leaves especially on first cutting. In this study, mortality of alfalfa weevil larvae and adults and damage reduction on plant leaves were assessed by using the recommended concentrations of some combinatory and botanical insecticides including lufenuron+ emamectin benzoate (Proclaim fit®), lufenuron+fenoxycarb (Lufox®), thiacloprid+deltamethrin (Proteus®), and azadirachtin (Neem-Azal®). Numerous observations were made on the mortality of insect larvae and adults and also the number of damaged (eaten) leaves of plants on one day before spraying (control) and 1, 3, 7, and 15 days after spraying. A factorial experiment with RCB design was adopted with three replications in Nagadeh suburbs in the spring 2018. Results showed that there was a significant difference in efficacy of used insecticides with control. lufenuron+emamectin benzoate and lufenuron+fenoxycarb had higher lethality on larvae with more than 95% after 15 days of treatment. Lufenuron+fenoxycarb along with lufenuron+emamectin benzoate and azadirachtin imposed more mortality adult alfalfa weevils. There were no statistically significant differences on the percent damages of larvae and adults among azadirachtin, lufenuron+emamectin benzoate and lufenuron+fenoxycarb treatments after 15 days. Considering the economic importance of weevil larvae especially in the first cut and the results of mortality and damage percent in different treatments, azadirachtin can be recommended as the most appropriate option in damage control of alfalfa weevil.