تأثیر تبوفنوزاید و فنوکسی کارب بر پاسخ‌های ایمنی سلولی کرم غوزه پنبه Helicoverpa armigera

The immune system of insects is divided into cellular and humoral responses, which provide a strong defense against invading agents. Using insect growth regulators (IGRs) is a suitable candidate for controlling insect pests due to their lesser side effects on humans and the environment. These compounds can disrupt the normal growth and development of insects by mimicking hormone functions such as juvenile hormone (JH) or ecdysteroids. The effects of some JH and ecdysteroid analogs on certain aspects of insect immunity have been identified, but the effects of tebufenozide and fenoxycarb on the cellular immune responses of the cotton bollworm Helicoverpa armigera remain unknown. Therefore, the present study aims to examine the impact of fenoxycarb and tebufenozide on the cellular immune responses of the larvae of the cotton bollworm. For this purpose, the total number of hemocytes, plasmatocytes, granulocytes, nodulation, and phenol oxidase enzyme activity were investigated in third-instar larvae exposed for 24, 48, and 96 hours to sub-lethal doses (LC10, LC25) and lethal dose (LC50) of fenoxycarb, which were 3.42, 5.43, and 9.12 mg per liter, respectively, as well as the sub-lethal (LC10, LC25) and lethal (LC50) doses of tebufenozide, which were 3.67, 6.88, and 10.51 mg per liter, respectively. Based on microscopic studies, five main morphotypes including prohemocytes, plasmatocytes, granulocytes, eosinophils, and spherulocytes were identified in the hemolymph of this pest. The results indicated that the total number of hemocytes increased after 48 and 96 hours of exposure to lethal and sub-lethal doses of tebufenozide, while this number decreased following the use of fenoxycarb. Furthermore, contrary to the suppressive effect of fenoxycarb on the immune system of this insect, the application of tebufenozide on the larvae of the cotton bollworm increased the total number of hemocytes, plasmatocytes, granulocytes, nodulation rate, and phenol oxidase enzyme activity. The lowest number of hemocytes, plasmatocytes, and granulocytes, as well as the lowest phenol oxidase activity, were observed 48 hours after exposure to LC50 concentration of fenoxycarb, whereas the highest levels of hemocytes, plasmatocytes, granulocytes, and phenol oxidase activity were observed 48 hours after exposure to LC50 concentration of tebufenozide. Overall, these results suggest that the immune response system is regulated by hormone-like compounds, in such a way that fenoxycarb can inhibit cellular immune responses while exposure to tebufenozide can enhance cellular immune responses.