جستجوی مقالات مرتبط با کلیدواژه "اثرات زیرکشنده" در نشریات گروه "گیاهپزشکی"

In this research, the efficiency of the parasitoid wasp, Habrobracon hebetor (Say) in integrated with Matrine and Bacillus thuringiensis (Berliner) subsp. Kurstaki (Btk) against Anagasta kuehniella (Zeller), was investigated. Lethal and sublethal concentrations (LC30) of Matrine and Btk were determined by bioassay method on host larvae. To evaluate the preference of the host larval instars by the parasitoid, different larval instars were provided for parasitoid and the rate of parasitism was determined. The fourth and the fifth instar larvae of the host were treated with sublethal concentrations of Matrine and Btk then were provided for parasitoid in choice and non- choice conditions. The rate of paralysis, parasitism, egg-laying, emergence percentage and sex ratio of release wasps were determined. The results showed that female parasitoid preferred the fourth and fifth instar larvae of the host for parasitism. In the choice test, Matrine-treated larvae were more preferred by female parasitoid while in non-choice test, the highest amount of parasitism and egg-laying was related to the control treatment. The emergence percentage of adult wasps and their sex ratio (Female/Total), obtained from Matrine-treated fourth and fifth instar larvae, were 61 and 54% in the choice and 61 and 54% in the non-choice tests. The results showed that Matrine and Btk have significant potential in controlling of A. kuehniella. However, due to the sublethal adverse effects of these control agents on the efficiency of the parasitoid, simultaneous use of them with the parasitoid wasp, H. hebetor is not recommended.

Liriomyza sativae Blanchard is considered as one of the most important pests of greenhouse and farm vegetables. According to the recommendation of using thiocyclam insecticide against the mentioned pest, in the present study the lethal and sub-lethal effects (LC10= 49.15, LC20= 87.1 and LC30= 131.5 a.i. mg/L) of thiocyclam insecticide (Evisect® SP50%) was evaluated on the biological parameters of this pest under laboratory conditions. The method used in the experiments was Leaf dip technique for leaves containing fly larva. Data analysis was performed using Age-stage two sex life table theory.  The results showed that adult lifespan/longevity was significantly reduced by sublethal concentration. Fecundity was also affected by the studied concentrations and the lowest amount of this parameter (34.23 eggs/female) was recorded in LC30 concentration. Accordingly, sublethal concentrations reduced the net reproductive rate (R0), and there were significant differences among the values of this parameter at all treatments tested when compared with control (control: 78.01, LC10: 63.76, LC20: 33.6 and LC30: 11.58 offspring/individual). Other parameters such as intrinsic rate of increase (r), finite rate of increase (l) were also significantly lower than the control. The highest estimated values for r and λ were recorded at control (0.19 and 1.21 day-1, respectively). Finally, with the reduced rate of development for individuals treated with sublethal concentrations, the mean generation time (T) was significantly higher in individuals exposed to any concentration tested, So that it was the lowest in the control with 22.49 days and the highest in LC30 with 26.25 days. The findings of the present research indicate that thiocyclam insecticide has a good potential in controlling the leaf miner in lethal and sublethal concentrations, and the importance of considering the role of sublethal effects when attempting to evaluate the total impacts of specific pesticide on an insect pest population and its natural enemy.

Brevicoryne brassicae is one of the most serious cabbage pests in the world. This pest feeds on the leaves, mostly on the host plant's middle leaves. Despite having many natural enemies, aphids are not entirely controlled by natural enemies due to their rapid reproduction. Applying chemical insecticides is one of the essential methods used to control aphids; using one pesticide to control several pests can reduce the costs and frequency of spraying. In this study, the lethal and sub-lethal effects (LC25) of matrine insecticide with a contact and stomach function on the cabbage aphid, were evaluated under laboratory conditions.

The dipping method was used in bioassay and life table studies against adults of aphid insects. The LC50 value of matrine insecticide for adults of cabbage aphid was 83.33 μl/ml after 24 hours, and LC25 concentration (30.11 ml/ml) was used to estimate the sub-lethal effects of matrine on the biological parameters of the cabbage aphid. Experiments were performed on the acephala variety of cabbage. One common method of investigating insecticides' non-lethal effects is demographic toxicology, which uses life table and growth population parameters to evaluate toxicity.

According to the results, the female lifespan/longevity and fertility affected by sub-lethal concentration were significantly reduced compared to the control (distilled water and citowett). The mean oviposition period of adult aphids decreased from 8.92 days in control to 3.79 days in LC25 concentration of the insecticide. The present study's data also showed that the sublethal concentration also affected the offspring of treated cabbage aphids. Accordingly, the sublethal concentration of matrine reduced the net reproductive rate (R0) from 23.96 nymphs per female in each generation in the control treatment to 3.26 nymphs in LC25. The intrinsic rate of increase (r) in sublethal concentration was recorded as 0.36 (day-1) and in control as 0.1 (day-1). Other parameters, such as finite rate of increase (l) and gross reproductive rate (GRR), were also significantly lower than the control. The mean generation time (T) of treatment affected by LC25 concentration of matrine increased compared to the control treatment.

Results of the current research in laboratory conditions showed that this insecticide has significant lethal and sublethal effects on the cabbage aphid. Therefore, matrine, as an herbal insecticide, can be considered in the management programs of cabbage aphids.

This research was carried out to investigate lethal and sublethal effects of commercial formulations of indoxacarb and lufenuron on survival, development and parasitism of Trichogramma brassicae Bezdenko under laboratory conditions (25±2 °C, 60±5% RH, and 16:8 h L: D). Each insecticide was applied at four concenterations including 1000, 750, 500, and 250 ppm (i.e. at recommended field application rate and three lower concenterations) and their effects were studied through three exposure methods, including contaminating adult’s food (honey solution 10%) with insecticides, residual contact, and dipping parasitized host eggs (in pre-pupa stage of parasitoid) in insecticide solutions. The results showed that both insecticides significantly increased adults’ mortality and decreased their longevity, fecundity, and emergence rate in comparison to control, and these adverse effects, increased with increasing applied concenteration. The highest mortality (52.5±6 percent), shortest longevity (1.72±0.1 days), and lowest parasitism rate (14.7±0.97 percent) were observed in those parasitoids that fed on solution contaminated with indoxacarb 1000 ppm. Dipping parasitized host eggs in recommended field rates of indoxacarb and lufenuron adversely affected prepupa survival, and reduced adult emergence by 19.7 and 19.3%, respectively. According to the IOBC categories of toxicity, both insecticides were found to be "slightly harmful" when they ingested through contaminated honey solution, and "harmless" when adult parasitoids exposed to their residuals and prepupae dipped in their solutions. Therefore, these insecticides are recommended as nearly safe products in biological control programs of lepidopteran pests with T. brassicae.

Green lacewing، Chrysoperla carnea (Stephens)، is an important predator of arthropod pests such as aphids، psyllids، thrips and whiteflies. Toxicity of endosulfan، imidacloprid and indoxacarb was assessed on male and female C. carnea in the laboratory. Contact bioassays were carried out in glass Petri dishes. The LC50 values for indoxacarb، imidacloprid and endosulfan were 0. 011، 0. 053، and 0. 343 g AI/L for males، and 0. 019، 0. 098 and 0. 398 g AI/L for females، respectively. Males were more sensitive than females to all three insecticides. To assess the sublethal effects، using IOBC (International Organization for Biological Control) method، adults were treated with LC25 of each insecticide. Analysis of variance did not show significant differences among treatments regarding the developmental time of the first، second and third instars، pupae and sex ratio. Differences between treatments and control were significant regarding pre-oviposition، oviposition and post-oviposition periods، fecundity، fertility، longevity of male and female. Mean longevity for control، imidacloprid، endosulfan and indoxacarb were 30 ± 2. 3، 24. 3 ± 3. 3، 21. 3 ± 2. 4 and 19. 7 ± 1. 4 days for males، and 36. 9 ± 2. 5، 31. 8 ± 2. 9، 27. 7 ± 1. 7 and 26. 7 ± 2. 6 days for females، respectively. The highest and the lowest rates of fecundity were 540 ± 49 and 206 ± 42 in control and indoxacarb، respectively. Based on the IOBC classification method، imidacloprid، endosulfan and indoxacarb were slightly harmful (%30 < Total Effect Index < %79) against adults. The adult stage was very sensitive to indoxacarb، imidacloprid and endosulfan. Hence، these insecticides should not be applied when the density of adults is high in the field.

Cryptolaemus montrouzieri Mulsant is the most important predator of the mealybugs in citrus orchards of northern Iran. In this study, the lethal and sublethal effects of different doses of chlorpyrifos+oil, abamectin, and chlorpyrifos+abamectin+oil on the adult ladybeetles were investigated under laboratory conditions. Each pesticide was applied at 25, 50 and 100% recommended field application rates (i.e. chlorpyrifos at 500, 1000 and 2000 ppm and abamectin at 50, 100 and 200 ppm concentrations) with 1% oil on 7-day old female ladybirds through three exposure methods, including topical direct contact, residual contact and feeding on sprayed preys. 24, 48, and 72 hours after treatment the parameters such as survival rate, mean of daily oviposition, and hatching percent of the eggs were measured. The results showed that chlorpyrifos+abamectin+ oil affected the survival rates through all three exposure methods, whereas chlorpyrifos effect on the survival rate was only observed in topical contact, and abamectin had no adverse effect on the adult survival. Among all treatments, chlorpyrifos 2000+abamectin 200 ppm had the highest adverse effect on female ladybird survival (with 16 percent mortality). In contrast to survival rate, mean daily oviposition, and egg hatching percent were significantly reduced in all three treatments and exposure methods, and this reduction continued until 72 hours after exposure. The lowest mean of daily oviposition (8.2 eggs per female) was observed 24 hours after feeding on preys treated with chlorpyrifos 2000 ppm+ abamectin 200 ppm+oil, and the lowest egg hatching rate (57.9 percent) was recorded 24 hours after topical contact with the same treatment. In conclusion, using field rates of chlorpyrifos and chlorpyrifos+abamectin with oil adversely affect survival and fecundity of the ladybird. So, it is necessary to use of pesticide in suitable time and spraying to increase compatibility between pesticide application and ladybird activity, in citrus orchards.