Effectiveness of Entomopathogenic Nematodes Steinernema tbilisiense and S. thesami against pest oak - Lymantria dispar (L.) and Tortrix viridana (L.)

Steinernematids and Heterorhabditids are lethal insect pathogens with biocontrol potential for managing insect pests of agricultural importance.The efficacy of entomopathogenic nematodes (EPNs) of Steinernema tbilisiense and S. thesami was evaluated by oak pests, such as Lymantria dispar L. (Lepidoptera: Liparidae) and Tortrix viridanaL. (Lepidoptera: Tortricidae). To determine the efficacy of nematodes under laboratory conditions, suspensions of the following concentrations were tested: 700 nematode, 350 nematode, and 200 nematode in 1 ml of water. The experimental objects were mainly L. dispar and T. viridana. In those experiments, where a suspension of S. tbilisiense 700, 350 and 200 nematodes in 1 ml of water was used against L. dispar, 96.5, 62.0 and 55.0% insect mortality were respectively recorded. When applying S. thesami - 98.0; 71.0 and 57.5% deaths.During the action of S. tbilisiense on the caterpillars of T.viridana, 95.5, 58.0 and 53.0% died. When using S. thesami, respectively, 90.5., 66.0 and 56.0%.The most effective concentration was 700 nem. in 1 ml of water, in which a maximum biological efficiency (99-100%) was achieved in a number of replicates.When using combined suspensions of two species of S. tbilisiense and S. thesami nematodes (350 N each per 1 ml of water) caused the death of 98.0% of L. dispar caterpillars, while the effectiveness of S. tbilisiense alone was 62.0% and S. thesami - 71.0%.The same high efficacy was observed when using this suspension against T.viridana - 92.0%.Thus, in the joint application of two species of nematodes, higher results were obtained than when each nematode was used separately. From this, we can conclude that in this case there is a phenomenon of synergism.Field surveys were conducted in Saguramo, Lelubani, Tezami (Mtskheta district).Oak trees were treated with suspensions of S. tbilisiense and S. thesami (700 nematode in 1ml of water). The best results were obtained in the fight against caterpillars of III and IV stages (mortality 62.5 - 65.2%).It was found that when using S. tbilisiense at 19-220 and relative humidity of 75 to 81%, the mortality of caterpillars of III and IV ages was 59%. In case of S. thesami, the mortality of caterpillars reached 64.5%.With an increase in the dose of nematodes in a suspension of up to 1000 nematodes in 1 ml of water, the effectiveness of the preparation also increased accordingly.The mortality of caterpillars in the case of S. tbilisiense reached 74.2%; when using S. thesami - 76.5%.On the basis of the conducted studies, it was established that the nematodes S. tbilisiense and S. thesami used in our experiments are equally effective against leaf-eating pests of oak. The effectiveness of nematode preparations varies with the temperature and relative humidity of the air. The main condition for obtaining high effects is high air humidity (above 80%) and an increase in the concentration of nematode suspension. It is proved the mortality of insect increases with an increase in the concentration of up to 1000 nematode 1 ml of water.