Evaluation of the efficiency of Trichogramma sp. and Bacillus thuringiensis var. kurstaki against the corn stem borers, Ostrinia nubilalis subsp. persica (Lepidoptera: Pyralidae), in corn fields of Moghan plain

The corn stem borer, Ostrinia nubilalis var. persica, is one of the most important pests in corn fields of Moghan plain. In order to decrease the undesired effects of using chemical compounds, recently, the application of biocontrol agents were increased in wide areas of Moghan. In this research, we evaluated the efficiency of biocontrol agents in pest management in 2008. The experiment was conducted in a randomized complete block by five treatments and four replication, including, Indoxacarb (Avant)®, Trichogramma sp. wasps, Bacillus thuringiensis var: kurstaki, integration of Trichogramma sp. and Bt., and check. In order to estimate the rate of parasitism, four days after releasing the parasitoid wasps, the number of parasitized eggs were recorded. In each plot, 20 plants were randomly considered for recording the number of the larval holes on corn stems. In addition, the number of the damaged stems was recorded on the same number of corn plants before harvest. Statistically analysis of the recorded data were carried out by using MINITAB software. In treated plots by egg parasitoid wasp, the range of egg parasitism rate was 22 to 28 percent. The number of larval holes were 1.05, 1.30, 1.55, 1.38, and 2.04 per plant in Indoxacarb, Bt., parasitoid wasp, integration of Bt. and Trichogramma sp., and check treatments, respectively. There was significant difference among the treatments considering the number of larval holes. The number of damaged stem in Indoxacarb, Bt, Trichogramma, integration of Bt and Trichogramma sp., and check treatments were 0.17, 0.59, 0.98, 0.80 and 1.60 per plant, respectively. There was significant difference among the treatments considering the number of damaged stems. Despite this, there were no significant difference among biological control treatments in the number of larval holes and number of damaged stems. The achieved results from present study were revealed that the effect of the egg parasitoid wasp, Trichogramma sp. is lower than examined Bt. Furthermore, the integration of the examined biological control agents had shown no synergistic effect against the pest.