Phenol-Oxidase Activity and Haemocytes Changes in Helicoverpa armigera Hübner Infected by Entomopathogenic Fungi, Beauveria bassiana and Metarhizium anisopliae

Entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae are important and effective biocontrol agents against arthropod pests. Compared to chemical insecticides, insect pests do not easily develop resistance against these fungi. In this study, the lethal effects of exposure to B. bassiana and M. anisopliae, effects on phenol-oxidase activity, total haemocyte count, and changes in granulocytes and plasmatocytes were evaluated in ۳rd instar larvae of Helicoverpa armigera. The LC۵۰ values for B. bassiana and M. anisopliae were ۰.۷۹۵×۱۰۶, and ۵.۹۷۲×۱۰۷ spore mL-۱, respectively. LC۳۰ and LC۱۰ of either entomopathogenic fungi were injected into the body of larvae, and ۲۴ and ۴۸ hours after injection, their hemolymph was extracted. After ۲۴ hours, the highest and lowest phenol-oxidase activity was observed in LC۳۰ of M. anisopliae, and LC۱۰ of B. bassiana, respectively. After ۴۸ hours of infection, phenol-oxidase activity increased in all treatments. At the LC۳۰ of M. anisopliae, the highest phenol-oxidase activity was recorded, and other treatments also showed a significant difference compared to the control. Five types of hemocytes including prohemocytes, plasmatocytes, granulocytes, oenocytoids, and spherulocytes were identified in the hemolymph of larvae. The highest Total Hemocyte Count (THC) was recorded in LC۳۰ M. anisopliae at ۹ hours after initial infection. The highest number of granulocytes and plasmatocytes were recorded ۹ hours after treatment in LC۳۰ of M. anisopliae and LC۳۰ of B. bassiana. Our results showed that both fungi had the ability to affect phenol-oxidase enzyme activity and haemocytes. These microbial insecticides exhibited high potential for controlling the pest.

کلیدواژه ها:

Bioassay ، Cotton bollworm ، Enzymes ، Microbial agents ، Physiological effect.