Effect of Heat Shock on Performance of Entomopathogenic Nematodes Strains Heterohabditis Indica and Heterorhabditis Bacteriophora" Inside Galleria Mellonella Larvae

Temperature is the most important factor affecting survival, infectivity, development, and reproduction of entomopathogenic nematodes, therefore, it is necessary to study the effect of heat shock on their penetration, development, and reproduction capabilities inside a target insect. The penetration capacity into Galleria mellonella larvae of the infective juveniles of two EPNs species; Heterorhabditis indica and Heterorhabditis bacteriophora, decreased as a result of exposing the IJs to the temperatures of 35oC and 40oC and relaxed for two days at 25oC compared to the control at 25oC. The decrease in penetration of IJs from both species was more significant at 40oC than that at 35oC. Furthermore, the IJs penetration capacity of the locally isolated strain H. indica was greater than that of H. bacteriophora strain, which was isolated from temperate climatic region, at both temperatures. However, the penetration capacity of H. bacteriophora IJs was improved as a result of preconditioning the IJs at 35oC before exposure to 40oC about 37 folds compared to 3 folds improvement in the penetration of H. indica IJs, when the obtained penetration rates were compared to values observed at 40oC. The development of the penetrated IJs to hermaphrodites was also decreased when the IJs were exposed to 40oC without preconditioning. The recovery to hermaphrodites did not exceed 45% of that in the control in both nematode species. While upon the preconditioning treatment, the percent of H.indica IJs developed to hermaphrodites was close to that of the control and the development of H. bacteriophora IJs was only 72%. These results indicate that preconditioning was less efficient in reducing the inhibitory effect of the lethal temperature 40oC on the development of H. bacteriophora IJs to hermaphrodites. The total reproduction of the IJs, expressed per IJ injected inside larva of Galleria mellonella, showed a tendency to decrease with the increase in the number of IJs injected inside the larvae at 25oC in both species. Also this decrease was observed with the temperature increase. The yield of the IJs at the density (26 IJs/ larvae) did not exceed 12 and 15% of that when 3 IJs per larvae were used at 35oC for H. indica and H. bacteriophora respectively. Preconditioning H. bacteriophora IJs improved their reproductive capacity by 2.6 and 3 folds compared to 1.8 and 1.1 folds in the reproduction improvement of H. indica IJs. This result supports our suggestion that preconditioning the IJs at 35oC before exposure at 40oC, gives the opportunity for heat shock proteins synthesis which plays a protective role in reducing the negative effects of stress such as, temperature and crowd ness.