نامه انجمن حشرهشناسی ایران (Feb 2009)
Lethal and sublethal effects of endosulfan, imidacloprid and indoxacarb on first instar larvae of Chrysoperla carnea (Neu.: Chrysopidae) under laboratory conditions
Abstract
The common green lacewing is an important natural enemy used for pest control in greenhouses. It is also very common in many agricultural systems. Hence, studying lethal and sublethal effects of insecticides on this predator would be useful. Toxicity of endosulfan, imidacloprid and indoxacarb was assessed on 1st instar larvae of Chrysoperla carnea (Stephens) in laboratory. Residual bioassays were carried out in glass Petri dishes. The LC50 values, for endosulfan, imidacloprid and indoxacarb were estimated 251, 24.6 and 133 mg ai/l, respectively. Imidacloprid was the most toxic among insecticides tested. To assess the sublethal effects, the 1st instars were treated with LC25 of each insecticide. Thereafter, these effects were studied using fertility life table experiments. The analysis of variance revealed significant difference between treatments and control with respect to developmental time of the 1st instar larvae. However, no significant difference was observed among endosulfan, imidacloprid and indoxacarb treatments considering the larval developmental time. Differences between treatments and control were not significant for the developmental time of the 2nd and 3rd instars, pupae, sex ratio, adult longevity, and adult fertility. The results showed that only net reproduction rate (R0) was significantly affected by treatments. The gross reproductive rate (GRR), intrinsic rate of increase (rm), doubling time (DT), mean generation time (T) and finite rate of increase (λ) were not affected. The highest and the lowest amounts of rm were 0.178 and 0.169 in control and indoxacarb, respectively. Imidacloprid was the most toxic of the insecticides tested on the 1st instar followed by indoxacarb and endosulfan. If results similar to laboratory findings are obtained in field conditions, these insecticides might be appropriate candidates for IPM programs.
