EL PARASITISMO DE COTESIA FLAVIPES INDUCE INMUNOSUPRESIÓN E INCREMENTA LA SUSCEPTIBILIDAD DE DIATRAEA SACCHARALIS A BACILLUS THURINGIENSIS

Abstract

Cotesia flavipes (Hymenoptera: Braconidae) is an important gregarious larval endoparasitoid of Diatraea saccharalis (Lepidoptera: Crambidae), a serious pest of sugarcane in Mexico and USA. During oviposition, the parasitoid wasp C. flavipes injects polidnavirus, venom, and parasitoid eggs into larvae of its Lepidopteron host, the D. saccharalis. This research analyzed cellular and humoral immunosuppression of D. saccharalis parasitized by C. flavipes in terms of hemocyte composition, encapsulation (using Sephadex A-25 beads) and nodulation (using E. coli) processes, and the activity of phenoloxidase (PO). Moreover, the effects of parasitism on the metabolic rates and food consumption were studied, and the susceptibility of parasitized and nonparasitzed larvae to different Bacillus thuringiensis ( Bt) strains was assessed in terms of larval mortality and pupation rates. The hemocyte types into granular cells, plasmatocitos, and others by morphological characters were classified. In both nonparasitized and parasitized larvae, the major hemocyte types were the granulocytes and plasmatocytes which consisted of 70–75% in the total hemocyte population. There were strong reductions of total hemocyte counts in parasitized larvae compared to those of the control group. D. saccharalis larvae showed a strong suppression of their encapsulation response to Sephadex A-25 beads and there was a reduction in the number of nodules in parasitized larvae. In terms of humoral inmune capacity, significant reductions in PO activity were detected in both hemocytes and plasma in parasitized larvae compared to unparasitized, indicating a significant decrease in humoral inmune response. The parasitized larvae showed significant decrease in total hemolymph proteins after 8 days of parasitization. Parasitism by the C. flavipes affects the growth and caused a decrease in weight gain and food consumption in D. saccharalis larvae, resulting in a lower final weight for parasitized hosts. Approximate digestibility and the efficiency of conversion of digested food of the parasitized hosts were also lower in parasitized larvae. The D. saccharalis parasitized by C. flavipes exhibited higher susceptibility to HD-73, HD-551 and HD-133 strains. This research demonstrates that the parasitism of C. flavipes adversely affects both celular and humoral immunity, and increases the susceptibility of D. saccharalis to bacterial infections