Comparative Study on Some Biological Indices of Agrotis ipsilon (Lepidoptera: Noctuidae) Larvae Treated with Three Control Agents under Laboratory Conditions

Aims: Sensitivity of Agrotis ipsilon towards three control agents: Runner, Tracer and local raw diatomaceous earth (silica nano-particles) were investigated.

Study Design: Evaluation of the effects of some insecticides on some nutritional indices of the black cutworm A. ipsilon.

Place and Duration of Study: Pests and Plant Protection Department, National Research Centre, Dokki, Giza, Egypt, within 2016-2017.

Methodology: Newly moulted 4th instar larvae were transferred individually into plastic cups (5 cm in diameter and 5 cm height) to avoid the cannibalistic behaviour then covered with muslin. These cups were divided into three groups each one was marked for one tested material, while the 4th group was marked as check (untreated control). Each one of the three groups was subdivided into three subgroups, each subgroup comprised 30 individuals to be represented for three concentrations (High, Medium and Low concentration). Each cup was provided with known weighed of fresh castor bean leaves treated with one of the abovementioned concentration of each tested material.

Nutritional indices were calculated using the following items: food consumption, weight gain, developmental time and percentage of mortality as well. Larvae were weighted before the experiment and repeated daily until the pupation or death. Weights were recorded daily; at the end of the experiment, all above recoded weights were expressed as percentage of dry masses and reweighted to reach a constant weight. The calculation of the nutritional indices as the following: Relative growth rate (RGR), the conversion of ingested food (Approximate digestibility (AD)), Efficiency of conversion of ingested food to body substance (ECI), consumption index and Efficiency of conversion of digested food into growth (ECD) were carried out according to the summarized equations.

Results: All the tested agents were found to be toxic to A. ipsilon, inducing significant mortality percentage at almost all tested concentrations. The physiological parameters (nutritional indices) affected by the tested agents were evaluated. Results showed that treated larvae reflected significant reduction in consumed food and growth. The approximate digestibility of treated larvae was insignificantly high for all treatments. Silica nano-particles insignificantly enhance the rapid mortality as compared with Tracer (insecticide) and/or Runner (IGR) at all tested concentration.

Conclusion: The growth rate was decreased when larvae consumed castor bean leaves dipped in IGR by increasing the concentration. This decrease in consumption rate is due to antifeedant, deterrent nature and toxic mode of action of IGR. Rearing of A. ipsilon larvae on host plant treated with IGR induced reduction in growth rate, efficiency in convert food to body mass and also, reduction in pupal weight. Depending on the obtained results, the IGR has adverse effect on A. ipsilon larvae. Thus, it can be used in the control program for the present insect pest, since the highest AD and the low ECD values lead to the retardation of growth.