فصلنامه تحقیقات آفات گیاهی
سال یازدهم شماره 2 (تابستان 1400)

Rice striped stem borer, Chilo suppressalis Walker (Lep.: Pyralidae) is considered as the most important pest in paddy fields in north of Iran and causes severe damages to rice cultivation. Currently, the use of chemical insecticides is the most common practice in controlling this pest. However, considering environmental problems, it is advisable to look for alternative methods, including the use of resistant or tolerant cultivars to rice striped stem borer. Thus in the current study 20 lines and cultivars of rice were considered. The results indicated that all 20 cultivars and lines tested in the first generation of rice striped stem borer showed dead hearts ranging from 15.29 to 21. 85% based on the standard evaluation system of rice (IRRI) and relatively stood in resistant group (Scale 5). In the second generation of the pest the infection symptom of white heads clusters depicted that the line number 4 was in the resistant group, and lines 2, 4, 5, 7, 13, 11, 14, 15 and 18 in relatively resistant group. The results of this study showed that cultivars and lines of 1, 3, 6, 8, 9, 12, 16 and 19 are grouped in a relatively sensitive group to rice striped stem borer. Our study also showed that the Gohar cultivar with 31.28% white heads in reproductive stage was placed in the sensitive group. Therefore, in the present study, line 5 (row 11(, line 14 (row 10) and line 37 (row 17) are recommended for breeding and integrated management programs for rice striped stem borer.

Edwardsiana iranicola Zachvatkin, 1945, also known as plane-tree leafhopper, has been observed on various hosts. This is the first report of the existence of the above species and its damage on plane trees in Ilam province. In this study, population fluctuations and spatial distribution of this pest on plane-trees in urban green spaces of Ilam province, were studied during the years 2019 and 2020. One leaf was selected as a sampling unit. Sampling was performed weekly by placing plane-trees leaves in a white plastic tray containing water, and then adult and nymphs were transferred with a soft brush into eppendorf tubes containing 75% alcohol. The damage of this leafhopper was seen as small white dots on the entire surface of the leaf, especially near the main veins. The results of population fluctuations showed that the adult, nymph and egg stages had two peaks in both years of sampling. Also, in both sampling years, the highest density of adults and nymphs were observed in the southern geographical direction. According to Taylor’s power law and Iwao’s methods, the spatial distribution of the pest for adult and nymph stages was random.

Whitefly (Trialeurodes vaporariorum West.) as a polyphage greenhouse pest with a large number of generations is one of the most important crop and greenhouse pests. In this study, the toxicity of emamectin, spinosad, buprofezin and imidacloprid on greenhouse whitefly and parasitoid wasps Encarsia formosa was investigated. The LC50 values obtained from the probit analysis of bioassay data as a result of the effect of different concentrations of emamectin, spinosad, buprofezin and imidacloprid on 3rd nymph stage of greenhouse whitefly after 24, 48 and 72 hours were (1.72, 1.33, 1.31 and 0.63), (1.40, 1.31, 1.27 and 0.44) and (1.15, 1.04, 0.93 and 0.31) ml L-1, respectively. According to these results, the most effective insecticide on 3rd nymph of whitefly was imidacloprid during 24, 48 and 72 hours and the least effective insecticide was emamectin. The results of analysis of variance and comparison of mean mortality due to treatments of emamectin, spinosad, buprofezin and imidacloprid on E. formosa after 5 days showed that buprofezin was the least dangerous and imidacloprid was the most dangerous insecticide for this natural enemy.Therefore, in integrated management of this pest, due to the ineffectiveness of buprofezin on E. formosa in comparison with other insecticides and also having high toxicity on the egg and 3rd nymph stage of the pest is recommended.

Epigenetic mechanisms such as histone changes, especially acetylation and deacetylation, play an important role making host-pathogen interactions by regulating gene expression, which is catalyzed by the enzymes histone acetyltransferase and histone deacetylase. Since one of the safe pest control methods is the use of pathogens, investigating the role of these mechanisms in response to insect pathogens plays a vital role in controlling pests. Studies have shown that histone deacetylase inhibitors affect the replication of mammalian pathogenic viruses. Therefore, in this study, the role of trichostatin as a histone deacetylase inhibitor in Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) virus replication and antiviral immune response in Sf9 cells was investigated. For this purpose, the cells were exposed to two concentrations of trichostatin (1 and 0.25 μM) one and three hours before or at the same time with viral infection and trichostatin effect on virus replication and some important immune system gene expression were investigated. The results showed that virus replication was not affected using this compound. Moreover, after using concentrations of 1 and 0.25 μM trichostatin, the expression level of primary genes of antiviral immune pathways (Ago2 and Dicer2) miRNA and siRNA (Ago1 and Dicer1) did not show significant difference compare with control. In conclusion, the replication of ACMNPV virus and the antiviral immune system in Sf9 cells did not affect by the epigenetic mechanism of histone deacetylation.

Cytoplasmic incompatibility (CI) is the most common reproduction manipulation induced by intracellular bacteria, Wolbachia which occurs when infected males mate with an uninfected female. The result of incompatibility in diploid species is embryonic death and in haplodiploid species, CI occurs in two ways: male development (MD) and female mortality (FM). The parasitoid wasp, Habrobracon hebetor infected with a Wolbachia- CI strain. In the present study, after removal of Wolbachia with antibiotic, the incompatibility type was determined by comparing the number of offspring, the number of male progeny and the mortality rate in different developmental stages in the compatible and incompatible crosses of H. hebetor. Also, the effect of temperature on CI intensity was investigated by comparing the number of offspring at 25, 30 and 35 °C in the compatible and incompatible crosses. The results showed that the number of offspring in the incompatible cross was less than the compatible cross and there was no difference in the number of produced males. Moreover, the highest mortality was observed in the egg hatching stage. Finally, high temperatures increased the number of offspring and decreased the severity of CI in the incompatible cross. Together, it can be concluded that CI type is female mortality in these parasitoid wasps. These results shed more light on the mechanisms underlying Wolbachia- host interaction.

The Mediterranean flour moth Anagasta kuehniella (Zeller) is used as a factitious host in mass rearing of biological control agents. In current study, the effect of different photoperiods on developmental time of immature stages and oviposition trends of A. kuehniella wereinvestigated. The experiments were carried out at 25±2oC ,65±5% RH and differents photoperiods including complete darkness, 16L:8D, 14L:10D, 24L:24D for immature stages and complete darkness, 24L:24D, 24L: rest in darkness, 14L:10D, 12L:12D and 12L: rest in darkness for female adult fecundity experiments. Results demonstrate that higher developmental time of embryonic developmental time achieve in full darkness (5.01±0.01 day) and in 24L:24D (5.00±0.02 day) which there was not significant different with others. Also, immature developmental time of A. kuehniella in darkness was significantly shorter (43.42± 0.64) than other treatments. Mean daily oviposition (52.13±3.22 eggs) and the total fecundity (323.60±10.99 eggs) were obtained in full darkness treatment. In according to this research condition, the darkness treatment, comparison with other treatments, is introduced as a best photoperiod for mass rearing of A. kuehniella.

The genus Stenchaetothrips Bagnall is belonging to the subfamily Thripinae with only one species in Iran. Here, the second species, S. faurei (Bhatti, 1962) is newly recorded from the country. Only two female specimens of this species have been collected on the rice fields from Ilam province (west of Iran). The color of body (mainly pale yellow), absence of campaniform sensilla on metanotum and the presence of compete comb on posterior margin of abdominal tergite VIII have been considered the most important characters of the species. Relevant illustrations and geographical distribution of the species are provided.