نشریه کنترل بیولوژیک آفات و بیماری های گیاهی
سال یازدهم شماره 1 (بهار و تابستان 1401)

The tomato leaf miner moth, Tuta absoluta (Meyrick) (Lep.: Gelechiidae), is one of the most important and destructive pests of tomatoes in fields and greenhouses and causes severe damage. The integration use of biological and chemical pesticides, with the aim of reducing the consumption and concentration of chemicals, and in order to lessen pollution in the environment and insect resistance, is considered. Therefore, this study aims to investigate the effect of different concentrations of Thiocyclam insecticide (Evisect® SP50%) and biological insecticide Problet® (Bacillus thuringiensis supsp. kurstaki), on the mortality of the 1st and 4th instar larva of T. absoluta with the aim of achieving the most effective insecticide mixture. For this purpose, experiments were performed with 0.5, one, and twice the recommended concentration of insecticides, and their combined use during 48 and 72 hours. The results showed that the mortality rate of the 1st and 4th instar larva of T. absoluta increased with increasing concentration and time of application of two insecticides. The LC50 values for the first and fourth instar larvae of T. absoluta were 15.13 and 32.80 ppm after 72 hours from the application of bacteria and Thiocyclam respectively. The recommended concentrations of insecticides caused 66.07 and 66.41% mortality in 1st larvae after 48 hours for Thiocyclam and bacteria respectively at half their recommended concentration (500 ppm). Thiocyclam + bacteria values for first and fourth instar larvae were 98.25 and 99.25%, respectively, at their recommended concentration (1000 ppm) after 72 hours.

Knowledge about natural enemy’s interactions in biological pest control programs in agricultural systems is important to increase their effectiveness. In this research, the effect of the pathogenic fungus, Beauveria bassiana (Hypocreales: Cordycipitaceae), on the fertility-life table parameters of the parasitoid wasp, Habrobracon hebetor (Say) (Hym.: Braconidae) was investigated. The experiment was conducted in a fully randomized design using 12 treatments in Twenty-five replications. The flour moth larvae were contaminated by four different conidia concentration (0, 103, 106, and 109 conidia/ml) of B. bassiana, then these larvae in three periods of 24, 48 and 72 hours after contamination were used as the host for female wasps. Based on results, larval and pupal periods of the wasps significantly increased under fungus application, so with increasing conidia concentration, larval and pupal periods increased from 2.94 and 6.36 days to 4.13 and 7.45 days, respectively. The adult longevity of female wasps decreased significantly from 18.97 days to 16.27 days by using B. bassiana. The intrinsic rate of population increase (r) and the finite rate of population increase (λ) of wasps showed a decrease with increasing the concentration of fungus and increasing time, while the mean generation time (T) increased from 16 days to 19 days by increasing conidia concentrations. Our results indicate that infection of host larvae with pathogenic fungus has a negative effect on the biological characteristics of parasitoid wasps and can reduce the efficiency of H. hebetor in pest control.

The predatory midge Dicrodiplosis manihoti Harris is one of the effective predators of cotton mealybug Phenococcus solenopsis Tinsely, which was reported from different regions of Khuzestan province. Since the mass-rearing and use of this predator in order to control the cotton mealybug requires identifying the best biological stage of the prey for feeding, in this research, the preference of the first, second and third instar larvae of D. manihoti mosquitoes by feeding on different stages of nymphs and adult cotton mealybugs at the optimal temperature of 32±1, relative humidity of 65% ± 10 and photoperiod of 14:10 hours (darkness: light) were investigated and the resulting data were analyzed using the Manly index. The comparison of the average Manly index showed that the larval stage of D. manihoti significantly preferred the adult of cotton mealybug to other growth stages, and the lowest consumption of this developmental stage was from the third-instar nymph without significant difference with the first and second instar nymphs (P<0.006, df=3,76 H=12.57). Meanwhile, the second and third instar larvae of predator significantly preferred the first instar nymphs to other developmental stages of pray and the lowest consumption of these developmental stages was significantly from the adult female. Feeding on the first instar nymph as an active growth stage and the main agent of transmission on hosts and other plants showed the importance of this predator in controlling the pest population and its control role.

Tomato leafminer, Tuta absoluta (Meyrick) (Lep.: Gelechiidae) is one of the important pests of tomato which causes heavy damage to tomatoes in the greenhouse and outdoor crops. In order to develop biological control of this pest, in the current study, the effects of Beauveria bassiana on different life stages of tomato leaf miner were evaluated in laboratory conditions. To investigate the effect of fungus on the length and survival rate of different stages of T. absoluta, the experiments were conducted in 10 treatments (control and different concentrations of fungal conidia) in three replications. The results showed that the egg stage and then the pupa are more sensitive to the fungus than the larval stages, and in different larval stages, young larvae are more sensitive to the application of the fungus than other larval stages. So the 50% lethal concentrations (LC50) of fungal conidia for different stages; egg, young larva, old larva and pupa was measured as 6×104, 1.16×106, 2×53.108 and 3.39 ×105 respectively. Also, the length of the larval and pupal periods of T. absoluta was affected by the application of B. bassiana, so that the length of the larval and pupal periods decreased from 51.31 to 44.12 days and from 6.64 to 5.33 days, respectively, by an increase in the concentration of fungal conidia. The results obtained in the investigation of the effect of B. bassiana on the mortality rate of different stages of T. absoluta showed that the mortality rate of all the different stages increased with the increase in the fungal conidia concentrations, so that at a concentration of 1010 conidia, the mortality rate of the different stages; egg, young larvae, old larvae, and pupae reached 89.65, 88.46, 60.71 and 90%, respectively. It was also found that by increasing the concentrations of fungal conidia, the survival rate decreased by passing of time in all stages of T. absoluta, and the survival rate increased with increasing age of larvae.