mehdi dastranj

Sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae) is the most important pest of wheat and barley in Iran. The aim of this study was to determine the resistance probabel levels of summer populations of Sunn pestcollected from Varamin (under the pressure of insecticides) and Gonbad (with no history of insecticide application) regions. Toxicity of the insecticides for the collected adults was measured using a topical bioassay. Treatments were performed under the pronotum with each insecticide in acetone for treatments and acetone alone for the control. The treated insects were maintained in laboratory conditions and mortality was recorded 24 hours after treatment. Fenitrothion LD50 values for Gonbad population males and females were 26.27 and 26.8 ug/insect, respectively. Varamin population LD50 values were also estimated 135 and 157.11 ug/insect for fenitrothion, respectively. LD50 values for deltametrin estimated for males and females of Gonbad population were 0.025 and 0.15 ug/insect. The values were also estimatid 0.47 and 1.75 ug/insect for males and females of Varamin population, respectively. Based on the overall results, Sunn pest showed reduced susceptibility of Varamin population to both insecticides studied. Although the susceptibility to deltamethrin was higher, its resistance ratio was also higher than fenitrothion concerning the probability of resistance development. The results obtained can be useful in Sunn pest control programs.

Glutathione S-transferase (GST) genes control vital traits for metabolism of the variety of toxins that expose insects to the environment (insecticide) or plant defense systems. Sunn pest is the most important pest of wheat and barley in the Middle East where it threats food security throughout the region. Sequencing the sunn pest's RNA provides an opportunity to identify the structure and function of the different gene families. To our knowledge, this is the first study to identify 43 GST candidate genes in sunn pest using bioinformatics tools. The identified candidate genes clustered in 5 cytosolic GST (Delta, Theta, Zeta, Omega, and Sigma) and Microsomal GST using phylogenetic analysis. The Sigma subclass was identified as the biggest subclass with 22 candidate genes, while microsomal GST found to be the smallest group with one candidate gene. Given the role of GST in the interactions among the insect, toxins, and environment, our results facilitate future investigations on insecticide resistance and their utilization in pest management programs against sunn pest.

The seasonal abundance patterns of the wheat spike aphids were studied by weekly sampling of five winter wheat fields in Gorgan region in northern Iran during two growing seasons، 2006 and 2007. Spatial distribution of different developmental stages and morphs of the aphids were described by fitting data to Poisson (random) and negative binomial (clumped) distributions، as well as by calculating dispersion indices. A sequential sampling plan was also developed using the fixed-precision method of Green for estimating the density of adults، nymphs and total population. Sitobion avenae (F.) and Schizaphis graminum (Rondani) were two main species infesting wheat spikes in this region. The first aphid colonies appeared on spikes during early April and peaked (16. 01±2. 86 aphid per spike) during early May. Based on R2 and F of regression analysis، Taylor’s power law provided a more adequate description of variance/mean relationships than did Iwao’s patchiness regression model، and the b values ranged from 1. 034 (alate adults) to 1. 545 (apterus adults). Aphid population، especially nymphs and apterous females، was aggregated during most of the growing season and negative binomial models fitted data sets better than the Poisson series. However، alate morphs showed a noticeable tendency to the random distribution and 63. 7 percent of their data sets fitted the Poisson distribution. Regarding sampling cost or required sample size، the developed fixed-precision sequential sampling plans showed an acceptable performance for estimating aphid density at the precision level of 0. 25. Optimum sample size was flexible and depended upon the aphid density and desired level of precision، and ranged from 25 spikes in density of 16. 01 aphids/spike to 268 spikes in 0. 168 aphids/spike at the precision level of 0. 25. The information presented in this study may be used in population management of aphids in wheat fields.