Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/26/2007
Publication Date: 2/21/2008
Citation: Chen, Y., Ruberson, J.R., Olson, D.M. 2008. Nitrogen fertilization rate affects feeding, larval performance, and oviposition preference of the beet armyworm, Spodoptera exigua, on cotton. Entomologia Experimentalis et Applicata. 126:244-255. DOI:10.1111/j.1570-7548.2007.00662.x. Interpretive Summary: Agronomic factors such as fertilization of crop plants can have a significant effect on insect-plant interactions. We studied larval development and oviposition preference of Spodoptera exigua, a generalist pest of many crops, on cotton plants that differed in their nitrogen content. Both larval growth rate and oviposition were enhanced on higher N plants. Higher nitrogen plants also grew faster and larvae preferred these plants over those with lower N, although they tended to eat more leaf tissue on the lower nitrogen plants. The chlorophyll content of leaves and petioles is strongly correlated with the amount of nitrogen in the plant, which can be used as a rapid determinant of the nitrogen in plants. Increased preference for plants with higher nitrogen suggests that judicious application of fertilizer may be needed to effectively suppress plant feeding damage by S. exigua.
Technical Abstract: Nitrogen (N) is one of the most critical chemical elements for plant and animal growth. Development and oviposition of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) was studied in relation to varying nitrogen levels in cotton, Gossypium hirsutum L. The development of S. exigua caterpillars fed upon plants with reduced N was prolonged in the lower N treatments (42, and 112 ppm N). Caterpillars reared on artificial diets underwent only 5 larval instars before pupation, but caterpillars reared on cotton plants, irrespective of the N levels, experienced a supernumerary 6th larval instar. Further, significantly more caterpillars reared on lower N cotton plants underwent supernumerary development compared to caterpillars reared on higher N cotton plants. Caterpillars inflicted little feeding damage on plants before they were 7-d-old, but fed heavily thereafter and the lifetime feeding damage per caterpillar ranged from 55 to 65 cm2, depending upon the N level of the food plant. Caterpillars distinguished between cotton plants with various N levels and fed preferentially upon higher N plants. Female moth oviposition choice was also affected by host plant N levels in the study -- cotton plants with higher N levels were preferentially chosen by S. exigua females for oviposition. The positive and negative effects of N on beet armyworm and cotton production are discussed based on these findings.