Temperature and dose-size effects on infectivity and reproduction of entomopathogenic nematode, Steinernema longicaudum Gongju Strain

온도와 농도가 곤충병원성 선충 Steinernema longicaudum 공주계통의 병원성과 증식에 미치는 영향

Effects of temperature and dose-size on infectivity and reproduction of Korean entomopathogenic nematode, Steinernema longicaudum Gongju strain were examined. The greater wax mea Galleria mellonella larvae were exposed to 5, 10, 20, 40, 80, and 160 infective juveniles/larva in $60{\times}15$ mm petri dishes and kept in $13^{\circ}C$, $18^{\circ}C$, $24^{\circ}C$, and $30^{\circ}C$ incubators. Each petri dish contained one larva weighed from 180 to 200 mg. Infectivity was observed everyday for 14 days and reproduction for 30 days. The infectivity of S. longicaudum was more influenced by temperature than by dose-size. Mortalities by S. longicaudum were lower at $13^{\circ}C$ at all concentrations but higher at $24^{\circ}C$ and $30^{\circ}C$ even at lower concentrations, 5 or 10 infective juveniles/larva. Lethal time was also shorter with increasing temperature and dosages. All host larvae died at $24^{\circ}C$ and $30^{\circ}C$ in 2 days at the rate of 160 infective juveniles per host while 83.3% of tested larvae died at $24^{\circ}C$ in 10 days and 90% at $30^{\circ}C$ in 6 days at the rate of 5 infective juveniles. Reproduction was also better with increasing temperature and dosages. The highest number of progenies was obtained at $30^{\circ}C$ in 6 days at the rate of 80 infective juveniles. However, progenies were not produced from cadavers at $13^{\circ}C$. Reproductive period was the shortest at $30^{\circ}C$ of all temperatures by 6 to 9 days. The results indicated that optimum temperatures for infectivity was $24^{\circ}C$ and $30^{\circ}C$ for reproduction.

충남 공주지방의 강변 잔디밭에서 검출된 곤충병원성 선충 Steinernema longicaudum 공주계통의 병원성과 증식에 미치는 온도와 접종농도의 영향을 알아보았다. 꿀벌부채명나방 유충 한 마리당 선충을 5, 10, 20, 40, 80, 160마리 농도로 처리하여 13, 18, 24, $30^{\circ}C$의 항온기에 보관하면서 14일간 치사율과 치사소요일수를 조사하였고, 동일 온도에서 30일 동안 감염태 유충의 증식수와 증식기간을 조사하였다. 그 결과 온도와 농도가 높을수록 병원성이 높게 나타났지만 농도보다는 온도에 의하여 더 많은 영향을 받았다. 즉, $13^{\circ}C$에서는 모든 농도에서 치사율이 낮았으나 $24^{\circ}C$와 $30^{\circ}C$에서는 5마리와 10마리의 낮은 농도에서도 높은 치사율을 나타내었다. 온도와 농도가 높아질수록 치사일수도 단축되어 $24^{\circ}C$와 $30^{\circ}C$에서 160마리 농도는 2일만에 기주를 100% 치사시켰으나, 5마리 농도는 $24^{\circ}C$에서 10일만에 83.3%, $30^{\circ}C$에서 6일만에 90%의 기주 치사율을 나타내었다. 유충의 증식은 온도와 농도가 높아짐에 따라 양호한 경향이었지만 접종농도간에는 유의성이 인정되지 않았다. 저온인 $13^{\circ}C$에서는 모든 농도에서 전혀 증식이 이루어지지 않았다. 증식기간도 $30^{\circ}C$에서 $6{\sim}9$일로 다른 온도와 비교하여 가장 짧았다. S. longicaudum 공주계통의 병원성 발현 최적 온도는 $24^{\circ}C$였고 증식 최적 온도는 $30^{\circ}C$였다.