فصلنامه تحقیقات آفات گیاهی
سال دوازدهم شماره 3 (پاییز 1401)

Dena County is one of the most important grape-growing area in the southwest of Iran. The dominant cultivar in this area is Askari and grapevine moth, Lobesia botrana (Denis & Schiffermüller, 1775), is major pest on this cultivar. The first generation of this pest has a high population and seriously damages the flowers. To investigate this cultivar’s tolerance to first generation injuries on flowers, a damage simulation experiment designed and carried out for two consecutive years. In the first step, the average number of bunch/tree and flower/bunch for each year calculated, accurately. Having these data, the experiments performed with seven treatments (removal of 0, 5, 10, 15, 20, 25, and 30 percent of flowers based on the calculated average number of flowers/bunch in each year) and four replications (each tree considered as one replication). At vintage time, harvested grape product weighed separately and analyzed for simple and combined analyses of variance. The results showed that Askari cultivar in Dena region had a good tolerance and could compensate completely for anthophagus generation damage to the blossoms so that no yield loss observed in the treatments. The ability to compensate for damage is achieved by reducing the natural shedding of flowers and increasing the berry’s weight. According to the obtained results, up to 30% removal of flowers on Askari cultivar in Dena region, there is no need for controlling the first generation, thinning the flowers also increases the quality of berry. However, it is necessary to study the higher levels of flower removal and then make a final decision about the damage threshold of first generation in the region.

Oxindole is an inhibitor of the eicosanoid signal leading to inhibiting the immune system of insects. One of the important problems of using biological agents such as Bacillus thuringiensis Kurstaki (BtK) is their low efficiency and slowness of effect. In this research, the effect of oxindole and Biolep® based on BtK, were investigated on toxicity, feeding indices, energy reserves, and digestive enzyme activity of Helicoverpa armigera Hubner (Lep.: Noctuidae) larvae. The results showed that oxindole increased larval mortality and decreased LC50 and LT50 values of Biolep®. The feeding indices of cotton bollworm were changed under the influence of sub-lethal concentrations of bacteria and oxindole. At the concentration of 0.5 g oxindole/ kg diet the relative growth rate (RGR) decreased and the approximate digestibility (AD%) increased compared to the absence of oxindole. The use of oxindole along with bacteria also decreased lipase activity. Glycogen as an energy reserve was adversely affected by simultaneous application of oxindole concentrations of 0.1 or 0.5 g.kg-1 and the sub-lethal concentrations of Biolep® compared to sub-lethal concentrations of Biolep® only. The results of this research showed that by adding oxindole as an inhibitor of eicosanoid signal and immune system to the diet of cotton bollworm, the effectiveness of Biolap® increased and the feeding physiology of the pest was affected.

Due to environmental pollution caused by chemical pesticide application, the use of eco-friendly methods such as induced resistance to manage insect pests is necessary. In this study, the induced resistance potential of gibberellic acid, with a concentration of 0.125 g/L, in cabbage was investigated against cabbage aphid Brevicoryne brassicae L. Population growth parameters of cabbage aphid, including intrinsic population growth rate (r), net reproduction rate (R0), finite population growth rate (λ), gross reproduction rate (GRR), and population doubling time (DT) affected by gibberellic acid were significantly reduced compared to the control group (P < 0.05). However, there was not any significant difference between gibberellic acid treatment and the control for mean generation time (T) and the mean fecundity per adult female. The mortality rate of nymphs and adult females, age-specific survival rate (lx), and age-specific fertility (mx) in gibberellic acid treatment were significantly decreased compared to the control (P < 0.05). The mortality rate of first-stage nymphs was higher than the control and other stages. The dispersal percentage of first-stage nymphs and adult females treated with gibberellic acid was increased compared to the control (P < 0.05). Based on the results of this study, gibberellic acid was effective for decreasing the population growth parameters of cabbage aphid, and it can be considered in the integrated management of the pest.

Potato tuber moth, Phthorimaea operculella (Zeller), is the most important pest in potato fields in the world and Iran. The use of appropriate agricultural and protection strategies to prevent oviosition of Ph. operculella on newly formed potato tubers at the end of the cropping season can be effective in reducing its damage. The effects of cover crops on damage reduction on newly formed potato tubers were investigated in a randomized complete block design with three replications during two years 2020 and 2021. After the senescence of potato foliage, the cover crops including of vetch (Vicia sativa), grass pea (Lathyrus sativus), rye (Secale montanu), and strengthening of the natural field vegetation were used as cover crops in the field. Tuber infestation (%) during two years in vetch, grass pea, reinforcement of field vegetation and rye was 8.00, 12.33, 26.33 and 26.17%, respectively and all treatments significantly reduced the damage on potato tubers when compared with control (39.17%). The number of larvae in the infested tubers showed a significant difference between treatments, and the treatments of vetch, grass pea, reinforcement of field vegetation and rye showed a lower larval density, respectively. Based on results, vetch is the most effective plant to cover the soil and prevent Ph. operculella oviposition on the potato tubers. Moreover, maintaining and strengthening of weeds in the field at the end of the growing season and after the drying of potato foliage could be a low-cost method to prevent damage by Ph. operculella on tubers in the soil.

The cotton mealybug, Phenacoccus solenopsis Tinsely (Hemiptera: Pseudococcidae), is an important pest of many plants in agroecosystems and urban green landscapes. In this study, potential of three isolates of Akanthomyces lecanii, isolates PAL6, PAL7, and PAL8, and an isolate of A. muscarius, isolate GAM5, to microbial biocontrol of this pest on Coleus blumei, as the pest host plant, were investigated under greenhouse conditions. The infested host plants to five last instar nymphs were treated using different conidial suspension concentrations (104,105, 106, 107, and 108 conidia/mL) of each isolate and the mealybug mortalities were recorded every day, for eight days. The mortalities were varied from 14.3% (isolate PAL7) to 1.79% (isolate PAL8). The highest mortality was observed in concentration of 108 conidia/mL of the pathogens. The highest mortality caused by the pathogens was recorded six days after treatment. Totally, conidial suspension concentration of 108 conidia/mL from A. lecanii PAL7 was the best candidate for microbial biocontrol of the mealybug among the pathogens causing 56.17% mortality in the pest population six days after treatment. The results can be used for developing microbial biocontrol of the cotton mealybug especially in greenhouse conditions.

Slug, Deroceras agreste is one of the most important lettuce pests in greenhouse and field conditions. Population fluctuations of this pest in Ghaemshahr (Mazandaran province) were studied by quadrat and trapping sampling methods in 2019 and 2020 in four lettuce fields. Investigations from September of one year (simultaneously with the start of the activity on weeds) to April of the following year (the end of the lettuce crop season) showed that after the egg hatch in September, the presence and activity of larvae is observed, which gradually increases their population from September until November and decreases from December to February. The population of adults was less than that of larvae in September and gradually increases until November. In December, the number of adults exceeds the number of larvae as the population of larvae decreases and they become mature. Then, until February the population decreases. At the beginning of the sampling in September and also in October and November from the autumn season, the population was higher than in other sampling months and the peak population of the slugs was observed in November with an average of 85±4.7 and 48±2.8 respectively for larvae and adults in the first year and 83±4.0 and 48±2.8 respectively for larvae and adults in the second year of the survey. Also, a positive and significant correlation was observed between the environmental factors, temperature and humidity, with changes in the slug population. Egg laying was on average 28.8 days after mating, the average number of eggs in each clutch was 30.14 and the percentage of hatched eggs was 90.2%. The results of this research, as one of the first studies on the density and fluctuations of slug, D. agreste population, can be useful in planning the management for control of this pest.

Camelina, Camelina sativa (L.) Crantz (Brassicaceae) is an oilseed plant that was imported to Iran in 2015. Camelina is a cold-tolerant oilseed crop with minimal input requirements. In this study, the population density of Thrips tabaci Lindeman and its effect on the yield of different lines of camelina were investigated under field conditions. In this regard, 136 lines of camelina cultivated in the farm and for sampling, each plant was considered as a sampling unit and the number of thrips was counted on each plant after tapping. The number of healthy and injured capsules and seeds were also counted in each line with three replications. The results showed that yield decreased with increasing percentage of injured capsules. In addition, the percentage of damaged seeds was negatively correlated with the yield of camelina lines and the percentage of injured capsules was positively correlated with the percentage of damaged seeds. The results of linear regression showed that the relationship between thrips population density and yield and percentage of damaged seeds was not significant, while a positive and significant relationship was observed between thrips population density and percentage of injured capsules, meaning that with increasing thrips density, percentage of injured capsules increased, as well. Based on the findings, line 54 was recognized as the most resistant line against T. tabaci which was a semi-sensitive, resistant and tolerant line in term of antixenosis, antibiosis and tolerance mechanisms, respectively.