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Title: Influence of drought stress on Mexican rice borer (Lepidoptera:Crambidae) oviposition preference in sugarcane

Author
item Showler, Allan
item CASTRO, BORIS - DOW AGROSCIENCE,CA

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2009
Publication Date: 4/9/2010
Citation: Showler, A., Castro, B. 2010. Influence of drought stress on Mexican rice borer (Lepidoptera: Crambidae) oviposition preference in sugarcane. Crop Protection. 29(5):415-421.

Interpretive Summary: The Mexican rice borer, which infests sugarcane and other crops as well as rice, has been observed to prefer to lay eggs on drought-stressed sugarcane plants than on well-watered sugarcane. Our study showed that the preference was linked to increased numbers of dry leaves, where eggs are mostly laid, and to enhanced nutritional status of the plant based on accumulations of free amino acids essential to insect growth and development. The oviposition preference also resulted in greater infestation of stalks by larvae, and numbers of adult exit holes in stalks indicated that drought-stressed sugarcane will produce more Mexican rice borer adults than well-watered sugarcane.

Technical Abstract: The Mexican rice borer, Eoreuma loftini (Dyar), has been spreading northward from Mexico and Texas sugarcane and rice, and invasion of Louisiana is projected. This study showed drought stress increases water potential in sugarcane plants and results in >3.4-fold more dry leaves than in well-watered sugarcane. Drought stress caused seven of nine detectable free essential (for insect growth and development) amino acids to consistently accumulate, and another was elevated in two of three assays. Several free “nonessential” amino acids also occurred at higher levels in drought stressed plants. Dry leaves were preferred by the Mexican rice borer for oviposition by >7.8-fold over leaves on well-watered sugarcane, likely because of heightened host plant nutritional quality in terms of free amino acids (FAAs). Gravid female Mexican rice borers, when presented with dry excised leaves from drought-stressed and well-watered plants of two sugarcane varieties, however, were unable to discern between the four treatments for oviposition. Hence, the pest requires intact sugarcane plants to differentiate, suggesting the importance of chemoreception for host plant selection. Greater numbers of larval entry holes in the drought-stressed plants indicate levels of stalk infestation, and the high numbers of adult exit holes indicate the heightened capacity of drought-stressed sugarcane to produce new Mexican rice borer generations. The two sugarcane varieties did not show major genotypic differences in FAA accumulations and Mexican rice borer oviposition. However, the use of other varieties by growers, especially drought tolerant cultivars, might suppress infestations.