Evaluation of the Effect of Some Biopesticides on Alfalfa Weevil Larva, Hypera postica (Gyllenhal.) in Laboratory and Field Conditions

Abstract

Alfalfa weevil (Hypera postica Gyllenhal.) control is traditionally based on the use of chemical insecticides. Due to the side effects of these compounds, there are many motivations for the use of integrated control methods, which may include the use of biopesticides (microbial and botanical). The result of the effect of seven doses  of the tested biopesticides (500, 1000, 1500, 2000, 2500, 3000 and 3500 ppm) under laboratory conditions indicated that the insecticides Azadiractin^® (1859.971 ppm) and Biobit^® (2000.57 ppm) were of the highest, while Basiokara^® (3178.697 ppm) and Naturalis^® (2973.246 ppm) were of the lowest lethality. Field experiments were carried out based on randomized complete block design with 10 treatments and 4 replications. The treatments included Palizin^® (2.5 mL/L), Azadiractin^® (2 mL/L), Tondaksir^® (2.5 mL/L), Basiokara^® (3 mL/L), Biobit^® (2.5 mL/L), Naturalis^® (3 mL/L), two-component treatments, Azadiractin^® (1 mL/L) + Basiokara^® (1.5 mL/L), Biobit^® (1.25 mL/L) + Tondaksir^® (1.25 mL/L), and the chemical insecticide Cypermethrin^® (2 mL/L) in two year studies (2015-2016). Water was used as a control treatment. Sampling was done before pesticide application and on the third, seventh and fourteenth days after application and live larvae were counted in each plot. The percentage of the efficacy was calculated by Henderson-Tilton equation. The analysis of variance showed experimental treatments were of significantly different impacts at a probability level of 1% over two years. Comparison of the average mortality rate of alfalfa larvae showed that the highest ratios of the insecticides Cypermethrin^® (69.375%), Azadiractin^® (57.875%) and Biobit^® (46.25%) were of the highest lethalities, while that of Naturalis^® (27.52%) and Basiokara^® (22%) led to the lowest mortalities of alfalfa weevil larvae. Based on LC₅₀ values and the results of field experiments, Azadiractin^® and Biobit^® are recommended as a high toxic insecticide useful in the integrated management of the pest in organic alfalfa production system.