Effect of crop seed water content on the rate of seed damage by red imported fire ants (Hymenoptera : Formicidae)

Red imported fire ants, Solenopis invicta Buren, are known to feed upon pla nted field crop seed; however, the relationship with varying levels of seed water content is not known. Lf red imported fire ants are feeding on plant ed seed during periods of slow seed germination, and if the seed are more p alatable or otherwise more easily damaged at elevated water contents, the r isk of crop-stand loss is increased. In this study, 5 types of field crop s eeds-wheat, Triticum aestivum L.; corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench; cotton, Gossypium hirsutum L.; and soybean, Glycine m ax L.-were exposed to red imported fire ants under laboratory conditions to measure damage caused by feeding. The seeds were dry and on moistened filt er paper for maximum rate of germination, and at 20, 40, and 60% water cont ents for various parts of the study. Moistened seed suffered 2-90 times mor e damage in 48 h than comparable dry seed. When commercial sorghum seed was tested at 4 initial water contents, seed damage increased approximate to 2 2 times over damage to dry seed. A model was developed to predict the feedi ng damage to commercial sorghum seed as a function of elapsed time and seed water content. The risk of feeding damage relative to germination increase d up to as much as 20 times when the initial water content was 60% compared with dry seed, except for corn damage. which was relatively insensitive to water content. We conclude from laboratory studies that crop-stand losses are likely to be most severe for wheat and grain sorghum when moistened see d are exposed to feeding by red imported fire ants.