Food Distribution and Storage in Colonies of Monomorium pharaonis (L.) (Hymenoptera: Formicidae)

Abstract

The distribution (between adult workers and worker larvae) and storage of dyed foods (one protein, two lipids, and three carbohydrates) were investigated in standardized Pharaoh ant, Monomorium pharaonis (L.), colonies (n = 250 workers, 2 queens, and 25–30 mg worker brood) in the laboratory. Two foods were in liquid form (peanut oil and 1 M sucrose) and four were in solid form (egg yolk, beef fat, table sugar, and corn starch). Workers did not actively recruit to table sugar, but in a concurrent study it was used as building material to fill nest openings. Moistened corn starch was ignored by foraging workers with little storage. Workers became satiated on 1 M sucrose before any solution was given to larvae. Peanut oil, like the 1 M sucrose solution, was rapidly distributed among and stored internally by adult workers. Unlike the 1 M sucrose solution given primarily to older larvae, peanut oil was distributed rapidly to all larval stadia. Workers showed weak recruitment to beef fat even after 7 d of starvation. Only a few workers showed evidence of feeding on beef fat and none was distributed to larvae. Storage of solid lipid (beef fat) was variable. Workers in two of five colonies stored large quantities of beef fat in piles inside their nests. In three colonies only trace amounts of beef fat were stored after 24 h. In contrast, workers consistently stored large quantities of excess solid protein (moist egg yolk powder) in piles inside their nests. Solid protein was fed to and consumed primarily by older larvae, and none was detected in young larvae or adult workers. Workers actively recruited to liquid carbohydrate (1 M sucrose) and solid protein (moist egg yolk powder) foods after 2 d of starvation. A 7-d starvation period was necessary for active recruitment to lipids (peanut oil and beef fat), but caused extremely rapid recruitment (too fast for accurate observation) to carbohydrate and protein foods. Thus, colonies were starved for 2 d prior to the introduction of protein or carbohydrate foods, and 7 d prior to lipid foods. Our results suggest that lipids may not be rapidly depleted in the metabolism of the Pharaoh ant. Thus, protein and liquid carbohydrates (using simple sugars) may play a more important role as components of insecticidal baits that are important in Pharaoh ant management. However, in field colonies that may be stressed for lack of food (which may commonly occur), an insecticidal bait formulated from oil may be readily accepted and effective.