Toxicological and biochemical basis of synergism between the entomopathogenic fungus Lecanicillium muscarium and the insecticide matrine against Bemisia tabaci (Gennadius)

Abstract

The sweetpotato whitefly Bemisia tabaci (Gennadius) was challenged with different combinations of matrine (insecticide) and Lecanicillium muscarium (entomopathogenic fungus). Our results revealed a synergistic relationship between matrine and L. muscarium on mortality and enzyme activities of B. tabaci. To illustrate the biochemical mechanisms involved in detoxification and immune responses of B. tabaci against both control agents, activities of different detoxifying and antioxidant enzymes were quantified. After combined application of matrine and L. muscarium, activities of carboxylestrease (CarE), glutathione-s-transferase (GSTs) and chitinase (CHI) decreased during the initial infection period. Acetylcholinestrase (AChE) activities increased during the entire experimental period, whereas those of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) decreased during the later infection period. The increased mortality and suppression of enzymatic response of B. tabaci following matrine and L. muscarium application suggests a strong synergistic effect between both agents. The strong synergistic effect is possibly related to the disturbance of acetylcholine balance and changes in AchE activities of the whitefly as both matrine and L. muscarium target insect acetylcholine (Ach) receptors which in turn effects AchE production. Therefore, our results have revealed the complex biochemical processes involved in the synergistic action of matrine and L. muscarium against B. tabaci.

Figure 1

(a) Carboxylestrase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in carboxylestrase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment.

Figure 2

(a) Glutathione-s-transferase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in glutathione-s-transferase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment.

Figure 3

(a) Acetylcholinestrase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in acetylcholinestrase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment.

Figure 4

(a) Chitinase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in chitinase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment.

Figure 5

(a) Superoxide dismutase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in superoxide dismutase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment.

Figure 6

(a) Peroxidase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in peroxidase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment.

Figure 7

(a) Catalase activities of Bemisia tabaci at different time intervals following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatment; (b) Linear regression analysis between fold changes in catalase activities and different days following matrine, Lecanicillium muscarium, and matrine + Lecanicillium muscarium treatments.