فصلنامه تحقیقات آفات گیاهی
سال چهاردهم شماره 3 (پاییز 1403)

Sesamia cretica Lederer is one of the most important pests of corn and sugarcane crops in Iran. To study the population fluctuations, spatial distribution, and sequential sampling plan of this pest, sampling was done weekly in maize fields of Andimeshk and Shush regions, during 2022 and 2023. To estimate the population of pest immature stages, the whole plant of maize was selected as the sample unit. The results indicated that this pest produced four generations annually on maize, with an average population of 1.56±0.285 and 0.38±0.134 per plant in the first year, and 0.52±0.102 and 0.65±0.246 per plant in the second year, observed in Andimeshk and Shush, respectively. The spatial distribution of S. cretica was determined by two regression methods, Taylor’s power law and Iowa’s models. Both methods showed that the distribution pattern of pest in maize fields across both regions was aggregated throughout the two years of sampling. To enhance the description of the data by Taylor's power law, parameters of this method were used to develop sequential sampling plan using Green’s method at precision levels of 0.1 and 0.25. In sequential sampling model, sample size required to determine pest’s mean population was decreased by increasing density and decreasing the precision level from 0.1 to 0.25. Based on these results, S. cretica due to its multigenerational characteristics, poses a significant threat to maize fields. In this context, spatial distribution indices can be effectively utilized to enhance sampling strategies aimed at accurately estimating the population of this pest.

In this study, the effect of three cucumber cultivars (Vihan, Shahab, and Saba) and two types of culture substrates (soil and hydroponic) was investigated separately on the functional response of 3rd instar larvae of Chrysoperla carnea (Stephens) to different densities (2, 4, 8, 16, 32, 64, and 128) of 4-day-old nymphs of Aphis gossypii Glover. The 3rd instar larvae of predator were starved for 16 h before the experiment. The experiment was conducted for 24 h in leaf cages at 25±2 ̊C, 65±5 % RH, and 16:8 h (L: D). Logistic regression analyses revealed that the functional response of the C. carnea to A. gossypii in all treatments was type II. The attack rate (a) of 3rd instar larvae of the predator in hydroponic culture treatments was significantly higher than the soil culture. The handling times (Th) of the predator varied from 0.1310 to 0.1665 h on different treatments.  The 3rd instar larvae demonstrated the highest feeding attack rate on A. gossypii when associated with the Vihan cultivar, followed by the Shahab and Saba cultivars across both culture substrates. The results revealed that the culture substrates and plant cultivars can affect the functional response parameters of 3rd larval instar of C. carnea.  Further research is necessary to gain a deeper understanding of how plant culture substrates and cultivars influence the interactions among cucumber, A. gossypii, and C. carnea.

Bacillus thuringiensis serves as an effective biopesticide in controlling specific pests. Nonetheless, exposure to solar ultraviolet (UV) radiation is a significant factor that contributes to the degradation of the spores and crystals of this bacterium. Therefore, research on protective compounds against UV radiation is essential. In this study, the effects of activated charcoal, graphene oxide, and nanographene oxide in preserving the pathogenicity of B. thuringiensis var. kurstaki (Btk) against ultraviolet radiation on the beet armyworm, Spodoptera exigua (Hübner) were investigated under laboratory and field conditions. The probit analysis of concentrations of Btk on second-instar larvae of the S. exigua after 48 and 72 hours in the laboratory showed that LC50 was 1149.62 and 729.13 ppm, respectively. Additionally, the study examining the impact of UVC on the pathogenicity of Btk indicated that larvae exposed to UVC-treated Btk experienced lower mortality rates compared to those exposed to the non-irradiated bacterium. The variance analysis regarding the impact of UV radiation on spore germination, when using protective agents in comparison to the control group, demonstrated that activated charcoal showed the more effective results. Additionally, an analysis of variance regarding the UV-protective properties of the treatments in preserving the effectiveness of Btk against second-instar larvae conducted under both laboratory and field conditions revealed that activated charcoal had a higher protective effect compared to other treatments. Based on the results, activated charcoal is recommended for use with Btk against this pest. Activated charcoal can be suggested for inclusion in formulations of this biopesticide to protect it from solar UV radiation

Oak trees (Quercus infectoria) are one of the main components of forest communities in western Iran and play a vital role in preserving water and soil in this region. Oak gall wasps (Hymenoptera: Cynipidae) cause gall on different parts of oak trees. This research was conducted to investigate the concentration of some plant metabolites in different tissues of oak trees and some leaf galls formed by gall wasps and their changes during the growing season in the Javanroud region. For this purpose, four types of galls (Neuroterus numismalis Geoffroy, Neuroterus quercusbaccarum L., Cynips divisa Harting, and Cynips quercusfolii L.), leaves containing gall, and healthy leaves were collected as a sampling unit from oak forests in Javanroud city. This study measured the concentration of some food compounds and secondary metabolites, such as soluble and insoluble sugars, total phenol, total tannin, and condensed tannin. The results of the variance analysis of the data showed that the concentration of different metabolites during the season in four different types of gall and the two investigated tissues were significantly different. The results showed that the peak concentration of carbohydrates and starch in all four types of galls and two types of plant tissue occurs in October, while the highest amount of total nitrogen and crude protein is found in September. Because gall tissue is considered the only food source for the gall-producing wasps, the quality of its food seems very important to them.

Tetranychus urticae Koch is one of the major pests of many agricultural crops. The application of effective pesticides with novel mechanism of action is one of the common strategies in integrated management programs. In the present study, the effect of different concentrations of cyenopyrafen were assesed on the biological parameters of the T. urticae in laboratory conditions (25±3 °C, 65±5% RH, and photoperiod 8:16 h (light: dark). The assessment was conducted through a spraying method and involved analyzing the age-stage, two-sex life table across two successive generations. The LC50 value of cyenopyrafen was determined to be 250.945 ppm for protonymph stage. Among the sublethal concentrations of LC10, LC20, and LC30, the LC30 concentration exhibited the most significant impact on biological and reproductive parameters. This concentration resulted in a decrease in the oviposition rate, a reduction in the duration of the oviposition period, and a shortened lifespan for both male and female individuals in the first generation. The sub-lethal concentrations of cyenopyrafen also affected the progeny of treated protonymphs and caused an increase in the duration of the egg, larvae, protonymph, and deutonymph stage and a decrease in the adult lifespan of the female from 22.26 to 18.21 days, and this process caused a reduction in the fecundity rate from 45.63 to 28.86 eggs and the length of the oviposition period from 17.13 to 13.17 days. Consequently, the intrinsic rate of population increase was diminished, recorded at 0.20±0.51 day-1 in the control group and 0.15±0.051 day-1 at the LC30 concentration, with the most pronounced negative impact observed at the LC30 level. The population growth trend observed at the LC30 sublethal concentration was slower compared to the control. It is advisable to examine the impact of cynopyrafen on T. urticae within both greenhouse and field conditions for its application in integrated management.

Melon fruit fly Myiopardalis pardalina (Diptera: Tephritidae) is one of the important pests of melon and cantaloupe in the melon farms of the Iran and its activity causes a decrease in the quantity and quality of the crop yields. Identification and use of resistant cultivars can be effective in control and reducing the damage of this pest. In the present study, the sensitivity of four melon cultivars (Sefidak, Firoozi99, Khatooni, and Helmindi) was investigated to damage of M. pardalina. Also, skin thickness and length of the fruiting period of these cultivars were evaluated. The lowest damage was observed in Sefidak and Firoozi99 cultivars (the average of damage is 18-20%). A positive correlation was observed between the fruiting period of the plant and the amount of pest damage, while there was no correlation between the skin thickness and the amount of pest damage. Based on the obtained results, Sefidak and Firoozi99 cultivars, as cultivars with relatively low damage, can be used in the integrated pest management program in melon farms in Sistan region.

The chickpea pod borer, causing major damage to chickpea (Cicer arietinum L.) crops in most chickpea-growing regions of Iran and is a key pest of this yield. This study aimed to introduce and evaluate novel, effective insecticides as alternatives. The research was conducted using a randomized complete block design with five treatments and three replications in rainfed chickpea fields of Markazi, Kermanshah, and West Azerbaijan provinces. Treatments included two concentrations of chlorantraniliprole (150 and 100 mL/ha), thiodicarb (750 g/ha), indoxacarb (250 mL/ha), and control (water spray). Sampling of live larvae was performed one day before spraying and 3, 7, and 14 days after insecticide application. The results showed that all tested insecticides were effective. On the seventh day after application, chlorantraniliprole at 150 mL/ha showed higher efficiency than other treatments by 95.8% ± 2.1, 86.4% ± 2.4, and 92.3% ± 4.6 in West Azerbaijan, Markazi, and Kermanshah provinces, respectively. Additionally, assessment of damaged pods revealed that in Markazi province, application of chlorantraniliprole at 150 mL/ha resulted in the lowest damage percentage. In Kermanshah province, indoxacarb followed by chlorantraniliprole at 150 mL/ha, proved to be the most effective while in West Azerbaijan province, both thiodicarb and chlorantraniliprole at 150 mL/ha were the most successful in minimizing pod damage. According to the obtained results, chlorantraniliprole is recommended for inclusion in management programs of this pest in chickpea fields.