تاثیر نماتودهای بیمارگر حشرات Steinernema carpocapsae و S. feltiae روی کرم برگخوار چغندر Spodoptera exigua

Entomopathogenic nematodes (EPN) from the family Steinernematidae are obligate insect pathogen, capable of infecting and killing a number of economically important insect pests. EPNs can be considered useful biological control agents due to high virulence, efficient host strategy, ease of mass production and safety towards non-target organisms. Different species and isolates of EPNs show different levels of efficacy against pests. Beet armyworm, Spodoptera exigua, is one of the most important cosmopolitan and polyphagous pest that cause serious damage. This pest is mostly controlled using synthetic insecticides then effective alternatives to synthetic insecticides such as biocontrol method need to be developed to reduce the pressure for insecticide resistance development and to reduce negative effects of the insecticides on natural enemies of pests and other non-target organism including humans. With the aim of evaluate the efficacy of native isolates of Steinernema carpocapsae and S. feltiae, 24 hours beet armyworm larvae susceptibility were studied using filter paper assays during 72 hours of post infection. EPNs efficacy were studied using seven treatments including 6, 12, 50, 100, 200 and 300 across four replications. Control treatment received only Ringer's solution. Beet armyworm mortality under treatments of both EPNs species were significantly affected. Unlike S. feltiae (F6, 21 = 7.9; P < 0.05) in which the mortality reached to its highest rate (60%) at 100 IJs/L concentration after 24 hours of post infection, larvae mortality exposed to S. carpocapsae (F6, 21 = ; P < 0.05) increased up to 200 IJ/L (100%) then plateau, at the same period, lowest rate of mortality of both EPNs were recorded at 10% IJs/L. By increasing the post infection period, mortality increased, after 72 hours and under S carpocapsae treatment, highest (%100) and lowest (%60) mortality were recorded at 200 IJs/L and 7 IJs/L respectively, these values for S. feltiae were 100 and 70 recorded at 25 IJs/L and 7 IJs/L respectively. In our results S. feltiae appeared as a more efficient EPN against 24 hours larvae. These differences in virulence can be attributed not only to EPNs inter-specific differences but also to their symbiotic bacteria or host strategies.