Laboratory evaluation of temperature effects on germination, radial growth and sporulation of entomopathogenic fungi and on their pathogenicity to red spider mite, Tetranychus urticae koch

Entomopathogenic fungus (EPF) can provide safe and efficient insect pest management. Temperature, relative humidity (RH), light, air, nutritional content and host physiological condition are all elements that impact the proliferation and virulence of entomopathogenic fungus. The current study aimed to evaluate the effect of different temperatures on germination, growth, sporulation of entomopathogenic fungi and on their pathogenicity against Tetranychus urticae Koch was studied.

Laboratory experiment was conducted to study the impact of temperature on germination, radial growth and sporulation of five entomopathogenic fungal isolates viz., B. bassiana (Bb 111), B. bassiana (Bb 112), B. bassiana (Bb 113), B. bassiana (Bb 114) and M. flavoviride var. minus. Virulence of five entomopathogenic fungal isolates subjected to different temperature against T. urticae also evaluated through laboratory bioassay techniques.

Results one valuation of entomopathogenic fungal isolates with four different temperatures at 20°C, 25°C, 30°C and 35°C showed that 25°C was optimum for germination, radial growth and sporulation. Maximum germination was recorded with the entomopathogenic isolate Beauveria bassiana (Bb 112) (95.67%) at 25°C. Interestingly, at 25°C all the B. bassiana isolates showed a radial growth of more than 50 mm with the highest recorded as 84.67 mm by B. bassiana (Bb 111). Maximum spore production was observed with B. bassiana (Bb 112) at 25°C (1.63×10⁶ spores ml⁻¹) followed by B. bassiana (Bb 111) (1.45×10⁶ spores ml⁻¹). It was also the most pathogenic against T. urticae at 25 and 30°C. The isolate Bb112 grown at 25°C caused higher mortality of 97.57 per cent against T. urticae. From the findings the isolates of B. bassiana (Bb 112) and (Bb 111) were found promising bio control agent against T. urticae with varying temperature.