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Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/4/2003 Publication Date: 9/1/2003 Citation: Showler, A., Moran, P.J. 2003. Effects of drought stressed cotton, Gossypium hirsutum L., on beet armyworm, Spodoptera exigua (Hubner), oviposition, and larval feeding preferences and growth. Journal of Chemical Ecology. 29(9):1997-2011. Interpretive Summary: The beet armyworm has been anecdotally reported to oviposit more on drought stressed than on non-stressed cotton plants. In this study, beet armyworms laid more eggs on drought stressed than on well watered plants, but larvae were heavier on the non-stressed plants. Although drought stressed leaves had greater amounts of soluble proteins, free amino acids, and soluble carbohydrates, water was the limiting factor for larval growth and development. Technical Abstract: The beet armyworm, Spodoptera exigua (Hubner), has been reported to oviposit more on drought stressed than on non-stressed cotton plants. Using potted cotton plants in cages, this study demonstrated that beet armyworms deposited 3.3, 4.6, and 2.3 times more (P less than or equal to 0.05) eggs on cotton plants that were grown on 1,500, 1,000, and 750 ml water/wk, respectively, than on those grown in well watered soil. Third instars, however, showed no preference for stressed cotton foliage over non-stressed foliage. Third instar beet armyworms raised on well watered cotton plants were 1.5, 2.3, and 2.6 times heavier than those reared on cotton grown in the 1,500, 1,000, and 750 ml water/wk plants (P less than or equal to 0.05), respectively. Physiochemical analyses showed that drought stressed leaves had significantly greater amounts of free amino acids that are essential for insect growth and development. Soluble protein and soluble carbohydrates were also more abundant in stressed leaves compared to non-stressed leaves. Despite the apparent increase in nutritional quality in drought stressed plants, larval survival was reduced because the limiting factor became water. Greater amounts of cotton leaf area were consumed from drought stressed leaves (P less than or equal to 0.05) than from non-stressed leaves, probably because the larvae had to metabolize greater portions of assimilated energy to supplement body water with metabolic water derived from respiration. The association of host plant nutritional quality to oviposition preference, and conversely, to reduced survivorship, is discussed. |
