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

Authors: CHEN, YIGEN - University Of Georgia; RUBERSON, JOHN - Kansas State University; Ni, Xinzhi

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2013
Publication Date: 3/1/2014
Citation: Chen, Y., Ruberson, J.R., Ni, X. 2014. Influence of host plant nitrogen fertilization on haemolymph protein profiles of herbivore Spodoptera exigua and development of its endoparasitoid Cotesia marginiventris. Biological Control. 70:9-16.

Interpretive Summary: Nitrogen fertilization can influence plant-pest-beneficial insect interactions in a crop field. The influence of low nitrogen fertilization on insect herbivores can be amplified in the parasitization or predation of the crop pests. In the present study, we examined the impact of four levels of nitrogen fertilization treatments of the cotton plants on the interactions between the beet armyworm and a parasitoid wasp. The experiment showed that the percentage of the parasitoid wasp offspring developing to emerge from the larvae and spin a cocoon, and total mortality of parasitized beet armyworm larvae were unaffected by the varying nitrogen levels. The developmental time of the wasp larvae in the beet armyworm larvae feeding on lowest nitrogen-treated cotton plants was approximately 30% longer than that of those feeding on the plants treated with three relatively high levels of nitrogen fertilization. The size of the male wasps was positively affected by the nitrogen level. Total amounts of the beet armyworm proteins were not affected by the nitrogen level, but were reduced by the wasp parasitism. Two dominant proteins in the beet armyworm larvae were affected differently. The concentrations of the protein with high molecular weight were unaffected by the nitrogen treatments, whereas parasitism reduced it. In addition, the concentrations of the protein with low molecular weight were interactively affected by both parasitism and nitrogen treatment, that is, the three higher nitrogen fertilization levels increased protein concentrations when compared to the lowest nitrogen treatment in the non-parasitized beet armyworm larvae, whereas nitrogen treatment had no effects on the wasp-parasitized larvae. In the beet armyworm larvae feeding on the plants treated with the lowest nitrogen fertilization, parasitism increased the dominant protein with low molecular weight, while the cotton plants treated with three high levels of nitrogen fertilization and the wasp parasitism of the beet armyworm larvae decreased concentrations of the protein. Possible mechanisms and ecological consequences for the extended development of the wasp inside the beet armyworm hosts grown on low-nitrogen treated plants are discussed.

Technical Abstract: Nitrogen has complex effects on plant-herbivore-parasitoid tri-trophic interactions. The negative effects of host plant with low nitrogen fertilization on insect herbivores in many cases can be amplified to the higher trophic levels. In the present study, we examined the impact of varying nitrogen fertilization (42, 112, 196, and 280 ppm) on 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 (42 ppm) nitrogen cotton plants was approximately 30% longer than that of those feeding on high (112, 196, and 280 ppm) 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 haemolymph proteins were not affected by nitrogen level, but were reduced by parasitism by C. marginiventris. Two proteins with molecular weights of ca. 84 and 170 kDa dominated the S. exigua larval haemolymph proteins. Concentrations of the 170 kDa haemolymph protein were unaffected by nitrogen treatment, but parasitism reduced concentrations of the the 170 kDa protein. Concentrations of the 84 kDa protein, on the other hand, were interactively affected by parasitism and nitrogen treatment: higher nitrogen fertilization (112, 196, and 280 ppm) increased protein concentrations relative to the 42 ppm treatment for unparasitized S. exigua larvae, whereas nitrogen treatment had no effects on parasitized larvae. For S. exigua larvae feeding on 42 ppm nitrogen plants, parasitism increased concentration of the 84 kDa protein, while for those feeding on 112, 196, and 280 ppm nitrogen plants, parasitism decreased concentrations of the protein. Possible mechanisms and ecological consequences for the extended development of C. marginiventris on S. exigua hosts grown on low-nitrogen plants are discussed.