h. barari

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.

Different species of weevils (Col.: Curculionidae) are found in oilseed rape fields, which some of those are canola stem-borer weevils. They feed inside petioles, crown and/or stems of the crop in larval stages and cause damage. These weevils are mainly belonging to genus Ceutorhynchus, which little information about their taxonomy, distribution and biology is available in Iran.

During 2016-2018, the biological characteristics of canola stem-borer weevils were investigated in canola fields of Mazandaran, Lorestan and Golestan provinces. In each province, three fields were selected for collecting samples. Yellow water traps were used for weekly collecting adult weevils from the fields during crop growing season. For collecting weevil-infested crops and determining infestation rate, 10 quadrates (0.5 × 0.5 m) were used per field. The adult weevils collected by the traps were identified and the pest biology as well as the infestation rates of the crop by the weevils were studied.

In this study, five Ceutorhynchid species were collected and identified: C. picitarsis and C. chalybaeus from Mazandaran, C. erysimi and C. pallidactylus from Golestan and C. sulcicollis from Lorestan, Mazandaran and Golestan. In late November, the adult weevils migrated to canola fields and after feeding and mating, the females deposited their eggs into main veins, petioles of the lower leaves or inside of the collar area of young canola plants and the emerged larvae penetrated into the host plant. The three larval instars of this pest fed inside host plant tissue during autumn and winter till mid spring season. The feeding activity of the first and second instar larvae were observed in late November and late December, respectively. Third instar larvae were found from beginning until mid-spring season. In late April, third instar larvae left the host plant, dropped in the soil for pupation and new generation adults emerged in May. These weevils are univoltine. The results showed that, the maximum infestation rates of oilseed rape by the stem weevils in Mazandaran, Lorestan and Golestan provinces was 20.1±0.89, 14.8±1.29 and 10.2±0.29 percent, respectively.

Determining the time of adult migration activity, oviposiotion and larval development of the weevils is an integral part of pest management strategy in oilseed rape fields. In this study, flight and oviposition activity of adults and also feeding activity of the first instar larvae were mainly observed in late November, which suggests this time as a suitable time for chemical control, if necessary. These weevils are mostly distributed around the Caspian Sea region (Mazandaran and Golestan provinces) however more investigations are required to conclude the existence of those in other parts of country.