A simple wheat germ diet for studying the nutrient requirements of the Indian meal moth, Plodia interpunctella (Hubner)

Authors: Silhacek, Don; Murphy, Curtis

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2004
Publication Date: 6/1/2006
Citation: Silhacek, D.L., Murphy, C.L. 2006. A simple wheat germ diet for studying the nutrient requirements of the Indian meal moth, Plodia interpunctella (Hubner). Journal of Stored Products Research. 42:427-437.

Interpretive Summary: Infestation of processed cereal products by Indianmeal moths prior to reaching the consumer is a major loss to the milling industry. These losses may become greater when methyl bromide use is discontinued and other pesticide restrictions continue to tighten. Scientists at the USDA, ARS, Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, found that pesticide use can be decreased or eliminated by extending the growth rates of insect pests. Growth rates of Indianmeal moths can vary widely depending upon the nutritive and physical qualities of the processed cereal product. Wheat germ when supplemented with ca. 20% glycerol transformed from a cereal that was marginal to one that was optimum for larval growth. We investigated this observation and found that the accelerated growth was the result of an elevated water content in the diet along with an assimilatable source of energy, both of which were provided by adding glycerol to the wheat germ. For optimum Indianmeal moth growth cereal products should contain about 22% water and about 20% of a simple sugar such as glucose, fructose or sucrose for energy. The reduction of either or both of these components in a processed cereal product would reduce the product damage incurred by these moths.

Technical Abstract: The quantitative relationship of dietary water to the growth of the Indianmeal moth was investigated using a system where moisture content in the diet was established by the interaction of glycerol levels in the diet and the relative humidity in the air. The growth and development of the Indianmeal moth was strongly dependent upon the content of dietary water. Glycerol provided a suitable adjunct that raised dietary moisture levels. Increasing moisture levels in the diet generally increased the larval growth rate and larval size. The fastest growth rate and largest larval size on a 20%-glycerol/wheat germ (w/w) diet was observed when dietary moisture was ca. 25% (w/w). Increasing dietary moisture to 35% was achieved with 40% glycerol, but the diets were not suitable for larval growth. Glucose, substituted for glycerol was not effective in increasing dietary water or stimulating growth. We conclude that glycerol increases the larval growth rate and the larval size on wheat germ by increasing both, the amount of water and the amount of assimilatable energy in the diet.