Liquid feeding in the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae)

In order to accurately test liquid bait effectiveness in the lab, we determined that a starvation time of 96h is more appropriate than 72h of starvation time for laboratory fire ants (Solenopsis invicta Buren) to better simulate foraging ants in the field. Densities and viscosities of two commercial baits and 20% sugar water at 25C were measured then compared to amount of material consumed per ant at these physical properties. Mean densities of 20% sugar water, Dr. Moss, and Terro were 1.051, 1.287, and 1.354 g/mL, respectively, and viscosity of each bait treatment varied in the same order but more drastically (1.7, 32, 400 centipoise, respectively). Ants that feed on formulated baits exhibit feeding behaviors different from those which occur when feeding on sugar water. At first glance, one might conclude that the difference is due to the toxicant, but our findings suggest that physical properties of baits may be a factor in this change in feeding behavior. In order to determine the effect of liquid physical properties on feeding, the method of liquid feeding was first determined. Next, sucrose solutions were prepared to test effects of viscosity and sucrose concentration on Solenopsis invicta separately. Solutions containing boric acid were also prepared to record the toxicant effect in these tests. Individual ants were offered a droplet of solution, then amount taken and time was recorded. Fire ants used suction to feed, whereas lapping movements of the glossa were not observed. Initial weight of ants explained about 40% of the variability in total crop load. Total crop load was found to depend on viscosity as well as initial ant weight. As viscosity increased in a 30% sucrose solution, relative crop load and intake rate decreased. According to these results, individual ants feeding from solutions without boric acid will leave with a total crop load that is 54% dependent on individual motivation whereas the crop load of ants feeding from a 0.5% boric acid solution only 46% depended on individual motivation. One explanation may be that boric acid solutions in this study acted as unique food sources