Differential immunomodulatory effects of tebufenozide and fenoxycarb on cellular immunity in Helicoverpa armigera (Lepidoptera: Noctuidae) larvae

Abstract

Insect growth regulators (IGRs) such as tebufenozide (an ecdysone agonist) and fenoxycarb (a juvenile hormone analog) are widely used in pest management, but their immunomodulatory effects remain poorly understood. This study investigated the impacts of these IGRs on cellular immunity in Helicoverpa armigera (Hübner, 1808) (Lepidoptera: Noctuidae) larvae, a major agricultural pest. To test this, the first day third-instar larvae were fed on diet containing sublethal (LC10, LC25) and lethal (LC50) concentrations of tebufenozide or fenoxycarb at 24, 48, and 96 h and different cellular immunity parameters were measured. The total hemocyte counts (THC), plasmatocyte and granulocyte counts, nodulation, and phenoloxidase (PO) activities significantly increased following feeding of tebufenozide. In contrast, fenoxycarb decreased all the measured immune parameters, reducing THC, plasmatocyte and granulocyte counts, also significantly impairing nodulation and PO activity. These findings demonstrate that tebufenozide and fenoxycarb exert opposing effects on H. armigera cellular immunity.