تاثیر زمان‌های مختلف در معرض قرارگیری بر کارایی حشره‌کش‌های‌ آبامکتین و آزادراکتین علیه کرم قوزه پنبه

The cotton bollworm, Helicoverpa armigera Hübner, is a major pest in cotton and one of the most polyphagous and cosmopolitan pest species that damage hosts economically. Integrated pest management program in which a variety range of approaches are used to gain sustainable control is supported due to its lower environmental impact and reducing resistance frequency in target population. Here the results of sub-lethal effects of Abamectin (Aba) and Azadirachtin (Aza) on immature stage of cotton bollworm during different exposure times are presented. Laboratory population was established using artificial bean-based diet. First instar 24 hours larva were involved in assays. Larvae were subjected to treatments by mixing treatments with appropriate amounts of diet. 15.62- 2000 ppm was characterized as a main concentrations range for Aba, this range for Aza was recorded as 100-800 ppm. Three sub-lethal doses from Aba including 100, 200 and 400 ppm and 62.5, 125 and 250 ppm in the case of Aza were involved in assay to test combination effects of both agents against H. armigera larvae. LC50 values of Aba were 477.24, 149.53 and 88.88 ppm when larva exposed for 24, 48 and 72 hours, respectively and dose –effect line slops were calculated as 1.12, 1.71 and 2.29 respectively. The results showed that toxicity increase 3.2 and 5.4 folds by increasing one and two days in larva exposure time to Aba, respectively. The dose-effect line became steeper as time increases. An interesting result was the independence of larval mortality with Aza concentration, after 72 h. of larvae exposure, lower mortality was recorded at higher concentration (35% mortality at 800 ppm) compared to lower one (55% mortality at 200 ppm). This situation was observed in combination treatments in which higher concentration of Aza (400 ppm) was used (Nearly 60% mortality at combination treatments contain 400 ppm and 90% at the present of 100 ppm of Aza after 72 h.). Combination treatments containing 200 and 100 ppm of Aza with 250 ppm of Aba caused significantly higher mortalities. It seems that lower toxicity of Aza at higher concentrations is probably the rational outcomes of its anti-feeding effect on larva.