Thermal tolerance mechanism of invasive cotton mealybug parasitoid, Aenasius arizonensis Girault (Hemiptera: Encyrtidae)

Abstract

The sustainability and fitness of biocontrol agents depends on the abiotic factors of which temperature is the most critical factor. Thermal stress affects parasitoid behavior owing to change in physiological activities. So, an experiment was conducted to know the effect of thermal stress on the antioxidant enzymes in Aenasius arizonensis (Girault), a specific parasitoid of cotton mealybug, Phenacoccus solenopsis (Tinsley). Enzyme activity in P. solenopsis and A. arizonensis at each thermal stress treatment was noticed. At 3 h of thermal stress, the temperature dependent increase in the SOD activity was observed. The maximum activity was noticed at 41 °C in both P. solenopsis and A. arizonensis compared to the 27 °C. The SOD activity was found more in four hours exposure compared to the three hours exposure at all the temperature treatments. Catalase activity was also found to increase with the increase in temperature, the effect of thermal stress was found to be significant in A. arizonensis and P. solenopsis for the activity of catalase. The maximum GST activity was found at 41 °C for both P. solenopsis nymphs and A. arizonensis adults exposed to different temperature treatments for 3 h of duration. However, all the temperature treatments for P. solenopsis nymphs were non-significant, whereas, for A. arizonensis, it was found significant for the GST activity. We observed that thermal stress had no effect on the concentration of MDA in both P. solenopsis and A. arizonensis subjected to different durations of temperature regimes. Elevated levels of SOD, CAT and GST might be providing possible protection against reactive oxygen species generated under elevated thermal stress.