Journal of Insect Physiology 46 (2000) 1103–1110 www.elsevier.com/locate/jinsphys Foraging in the ant Camponotus mus: nectar-intake rate and crop filling depend on colony starvation Roxana B. Josens a,* , Flavio Roces b a Departamento de Ciencias Biolo ´gicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pab. II — Ciudad Universitaria, (1428) Buenos Aires, Argentina b Zoologie II, Biozentrum der Universita ¨t Wu ¨rzburg, Am Hubland, D-97074 Wu ¨rzburg, Germany Received 28 June 1999; accepted 1 December 1999 Abstract The effects of colony starvation on the dynamics of nectar collection were studied in individual workers of the ant Camponotus mus. A laboratory colony was first deprived of carbohydrates for 15 days, and thereafter fed daily ad libitum with diluted honey until satiation. During these two successive experimental phases, the probability of feeding, crop filling and fluid-intake rates were recorded daily for individual foragers collecting a 10% (w/w) sucrose solution. The feeding responses of individuals varied with the nutritional state of the colony. When the colony was deprived of sugar, acceptance of the sucrose solution was higher than under satiation. Feeding time increased with increasing starvation. During deprivation workers fed nearly continuously on the solution, whereas a number of feeding interruptions occurred under satiation. Crop filling also increased with increasing starvation, and showed a marked decrease when the colony was satiated. Fluid-intake rate during the deprivation phase was roughly twice that during the satiation phase. This matched well with the difference in sucking frequency recorded during ingestion in satiated and starved workers, which was also higher during starvation. Results indicate that the responsiveness of foragers, determined by the nutritional state of the colony, influenced both foraging decisions and the dynamics of fluid intake.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Ant; Camponotus mus; Intake rate; Motivation; Starvation; Cibarial pump; Crop 1. Introduction Ants of the genus Camponotus feed on insects and carbohydrate solutions obtained from Homopteran honeydew and extrafloral nectaries (e.g., Levieux and Louis, 1975). Even though these sources are composed of sugars (principally sucrose, glucose and fructose), amino acids, lipids and secondary compounds (Baker and Baker, 1982; Bentley and Elias, 1983), sugar con- centration is one of the main variables affecting the indi- vidual foraging behavior of ants. In particular, the fluid- intake rate — i.e., the gross rate of energy gain — is largely determined by the sugar concentration of the fluid being ingested, and by its effects on feeding dynamics (Josens et al., 1998). Several theoretical models based on the Poiseuille * Corresponding author. Fax: + 54-11-4576-3384. E-mail address: walter@bg.fcen.uba.ar (R.B. Josens). 0022-1910/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII:S0022-1910(99)00220-6 equation have been developed to account for the dynam- ics of ingestion in fluid-feeding animals (Kingsolver and Daniel, 1979, 1983; Heyneman, 1983; Harder, 1983, 1986). Such models have taken into account the effects of the mechanical properties of the fluid (e.g., its density, viscosity, surface tension, etc.), the morphometry of the buccal apparatus, and the pressure differences exerted by the feeding system during intake. Regarding the feeding mechanics, Kingsolver and Daniel (1979, 1983) have distinguished two principal modes of fluid intake in insects: by suction as in butterflies, and by licking as in bees (and hummingbirds). While butterflies are assumed to feed continuously, bees extend and retract the glossa into the fluid, so that it adheres to the surface and sub- sequently reaches the functional mouth. In both cases, insects need to generate a negative pressure in the ali- mentary canal in order to transport the liquid into the cibarium. Such a difference is generated by the rhythmic contraction of transverse muscles that are inserted between the inner (buccal) and the outer (cranial) walls