Influence of host plant nitrogen fertilization on hemolymph protein profiles of herbivore Spodoptera exigua and development of its endoparasitoid Cotesia marginiventris

Nitrogen effects on cumulative percentage (mean±95% CI) of C. marginiventris forming cocoons due to fertilization levels of cotton leaves in the host’s (Spodoptera exigua) diet. •Low N fertilization of cotton plants slowed parasitoid development.•Parasitoid size was inversely related to N fertilization of plants.•2 proteins of ca. 84 and 170kDa, respectively, dominated host hemolymph proteins.•Parasitism reduced some hemolymph protein concentrations in Spodoptera exigua.•Nitrogen-poor plant diets of herbivores may significantly alter parasitoid fitness. Nitrogen has complex effects on plant–herbivore–parasitoid tritrophic interactions. The negative effects of low nitrogen fertilization in host plants on insect herbivores can be amplified to the higher trophic levels. In the present study, we examined the impact of varying nitrogen fertilization (42, 112, 196, and 280ppm) of cotton plants (Gossypium hirsutum L.) on the interactions between the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), and the hymenopteran endoparasitoid Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae). We predicted that the development and fitness of C. marginiventris would be adversely affected by low host plant nitrogen fertilization through the herbivore S. exigua. The percentage of C. marginiventris offspring developing to emerge and spin a cocoon, and total mortality of parasitized S. exigua larvae were unaffected by nitrogen level. The developmental time of C. marginiventris larvae in S. exigua larvae feeding on low (42ppm) nitrogen cotton plants was approximately 30% longer than that of those feeding on higher (112, 196, and 280ppm) nitrogen plants. Parasitoid size (length of right metathoracic tibia), a proxy for fitness, of C. marginiventris males was positively affected by nitrogen level. Total amounts of S. exigua hemolymph proteins were not affected by nitrogen level, but were reduced by parasitism by C. marginiventris. Two proteins with molecular weights of ca. 84 and 170kDa dominated the S. exigua larval hemolymph proteins. Concentrations of the 170kDa hemolymph protein were unaffected by nitrogen treatment, but parasitism reduced concentrations of the 170kDa protein. Concentrations of the 84kDa protein, on the other hand, were interactively affected by parasitism and nitrogen treatment: higher nitrogen fertilization (112, 196, and 280ppm) increased protein concentrations relative to the 42ppm treatment for unparasitized S. exigua larvae, wh