Control efficacy of Korean entomopathogenic nematodes against fungus gnat, Bradysia agrestis (Diptera: sciaridae) and persistence in bed soil

摘要

In recent years, the fungus gnat, Bradysia agrestis has caused serious problems on watermelon seedlings raised in propagation houses. Because of many chemical insecticides cause phyioioxic effects, alternative control measures are needed. Five Korean isolates of entomopathogenic nematodes strain, Steinerneniti carpocitpase Pochcon. S. glaseri Dongnae. S. longicaudum Nonsan. Heterorhabditis bacteriopliarct Hamnyang, and Heterorhabditis sp. Gyeongsan. were tested against this insect in the laboratoryand propagation house. The efficacy of B. agrestis, was different depending on nematode species, dosage, temperature, and larval stage of fungus gnat. S. carpocapase Pochcon strain was most effective among the tested nematodes. Control efficacies on thethird and fourth instars of fungus gnat were more susceptible than the second instar. Mortalities were higher at 25 and 30 deg C than 18 deg C. When S. carpocapasc Pocheon strain was treated with 160 infective juveniles (IJs)/larva, larval mortality was58 percent in the second instar. 95 percent in the third instar. and 98 percent in the fourth instar. respectively. When S. earpaeapase Pocheon strain was treated on the third inslar at the rate of 160 IJs, the mortality was 81 percent at 18 deg C. 95 percent at 25 deg C. and 86 percent at 30 deg C. respectively. Lowest LC_(50) value was represented by S. curpoeapase Pocheon strain, showing 4.3 Us in the third instar. and 4.2 IJs in the fourth instar at 25 deg C. The rate of larval reduction of B. agrestis, was above 70 percent even at the rale of 5 IJs/g. The nematodes persisted for 12 weeks in ihe media above 10 percent moisture. In addition, nemalodes persisted with high viability during the raising period of watermelon seedlings for 35 days and one week after transplanting to the field. The results show that Korean entomopathogenic nematodes. S. carpocapase Pocheon strain, in particular, is an effective tool for managing the fungus gnat larvae in propagation houses.