Comparison of the efficacy of insecticides, alphacypermethrin and lambda-cyhalothrin, against canola flea beetles

Background and Objectives
Flea beetles are the main pests of oilseed rape which the adult beetles cause damage via feeding on cotyledons and early leaves of crop. They gnaw small round holes into leaves, decreasing assimilation surface and slowing down plant's growth. Heavy damage at the early stage of cotyledons may destroy the plant. The critical period of damage on the crop is from germination and cotyledon stage until the appearance of 4–6 true leaves, later the damage is less harmful. Control of this pest mostly depends on using chemical pesticides via seed dressing and/or foliar application. This study aimed to estimate the effects of new chemical insecticides to control this pest in Iran.
Materials and Methods
To chemical control flea beetles, the project was carried out in a Randomized Complete Blocks Design with six treatments and three replications in the provinces of Mazandaran and Golestan in 2018. The treatments were alpha-cypermethrin 15% WDG, with two doses (300 g/ha and 150 g/ha), lambda-cyhalothrin CS10% (75 ml/ha), malathion EC 57% (600 ml/ha), thiacloprid OD24% (300 ml/ha) and control. Sampling and counting of the flea beetles were done 1 day before and 3, 7, and 14 days after treatment via counting the cached beetles on yellow sticky traps (one trap in the center of each plot) as well as the active beetles in a 0.5×0.5m quadrate in each plot center. Fourteen days after treatment, the percentage of infested plants and leaf surface damage were measured. The beetle's mortality was calculated by the Henderson-Tilton formula. Data were analyzed with SAS ver. 9 software, and the means were compared using Duncan. 
Results
All insecticides showed a significant difference at 1% probability level comparing with control. Alpha-cypermethrin with 300 and 150g/ha and lambda-cyhalothrin in Mazandaran and Golestan provinces with 87.17,84.19, 81.66; 76.66, 86.12, and 76 percentage efficacies had the highest effectiveness in control the pest, respectively. Malathion in Mazandaran and Golestan with 24.59% and 22.66% and thiaclopride 14.01% and 19%, respectively, were less effective in controlling and reducing flea beetles damage on the crop. Moreover, the percentage of infested plants was significantly different among insecticides 14 days after treatment at a probability level of 1%.
Discussion
Pest management of canola flea beetles faces ecological challenges and severe dependence on synthetic chemical pesticides. Insufficient soil moisture, late planting, unsuitable planting beds, and hot and sunny days with dry winds in the early growing stages of canola in autumn increase the damage and reduce the green area of the field in a short time. Due to the unsatisfactory effect of biological substances and plant compounds on canola flea beetles, chemical insecticides are one of the main options to reduce the population of this distractive pest in rapeseed fields. In various studies, in addition to chemical insecticides, biological compounds and botanical insecticides were tested to manage the control of pest. But in most cases, chemical insecticides were more effective. Therefore, determining the appropriate time for application and using effective insecticides are integral parts of the pest control strategy. This study's result showed that alpha-cypermethrin 15% WDG (150 and 300 g/ha) and lambda-cyhalothrin CS10% (75 ml/ha) could be used as new insecticides to control canola flea beetles.