Document Type : Complete paper

• Biocontrol of pests

Extended Abstract

Entomopathogenic nematodes (EPNs) are obligate parasites of insects and some other arthropods that cause the death of their hosts with the help of their symbiotic bacteria. Those nematodes are valuable biological control agents for pests. The compatibility of EPNs with insecticides is of great importance to use the mixture in the tank of sprayers or the simultaneous use of nematodes with insecticides in the integrated pest management (IPM) systems. On the one hand, such compatibility leads to economic savings in the application of control agents, and on the other hand, increasing the pest control percentage due to the combination of nematodes with insecticides, without increasing the concentration of insecticides, achieves positive economic and environmental benefits. The compatibility of EPNs is a species and isolates specific characteristics. In this research, the effect of bio-rational insecticide on the survival and pathogenicity of infective juveniles (IJ) native isolates of EPNs, Steinernema carpocapsae IRMoghan1, and Steinernema feltiae was evaluated. For the survival experiment, a suspension containing 500 IJml-1 of each nematode isolate was prepared in 150 milliliters of the recommended dose of flubendiamide (25 ppm). Then, five milliliters of the suspension were poured into Petri dishes (diameter 5.5 cm, in 30 Petri dishes). A similar concentration of IJ of both EPN isolates was prepared in distilled water and transferred into Petri dishes as a control. Petri dishes were sealed with Parafilm and incubated at 24 ± 1 °C in the dark for 24 hours, 48 hours, 72 hours, and seven days. At each time interval, five Petri dishes were examined for viability and pathogenicity of nematodes. For each treatment, in each time interval, 500 microliters of suspension were taken from Petri dishes in three replicates, and live and dead infecting larvae were counted under a stereomicroscope. Inactivated nematode larvae were considered dead if they remained motionless after stimulation. The experiment was repeated three times on three different days for each nematode isolate. The pathogenicity of the nematodes that were exposed to the flubendiamide was tested at each time interval. First, the prepared nematode-insecticide suspensions were washed three times with sterile distilled water to remove the insecticide residues. Then nematode suspension was prepared in distilled water (600 live and active nematode larvae per ml) for each treatment (each nematode isolate and control). Bioassay experiments on Galleria mellonella were performed in 12-well cell culture plates (length 12.3, width 8.25 and height 2.23 cm) which were covered with filter paper. In each well, 250 microliters of nematode suspension (150 IJ) and one last instar larva of G. mellonella were added. The plates were incubated at 24±1°C in the dark for 72 hours. Then, the mortality of G. mellonella larvae was recorded and to ensure the death of the insect due to nematode infection, the carcasses were dissected and the presence of nematodes inside the carcasses was confirmed. The results of variance analysis showed a significant difference in the percentage of mortality of two species of nematodes treated with flubendiamide insecticide (p<0.001) ; S. carpocapse IRMoghan1 showed higher mortality compared to S. feltiae due to flubendiamide treatment. Statistical analysis of the bioassay results of nematodes recovered from different time treatments with flubendiamide on G. mellonella larvae showed no significant difference between two nematode isolates (p˃0.05), although both nematode isolates caused higher mortality on G. mellonella than the control without nematodes. The high percentage of mortality of the larvae in the bioassay with flubendiamide-treated EPNs indicates the high efficiency of native isolates. Based on the results the native EPN isolates showed a high compatibility with flubendiamide, which is a valuable advantage for both Iranian isolates.