Nectar intake rate is modulated by changes in sucking pump activity according to the colony starvation in carpenter ants

FALIBENE, A.; GONTIJO, A.; JOSENS, R.

San Pablo, Brasil

Simposio; XVIII Simpósio de Mirmecología; 2007

Feeding dynamics has been deeply studied in fluid feeding insects. However, only in the carpenter ant Camponotus mus, the ability to vary the sugar solution intake rate was clear-cut demonstrated depending only on the individual responsiveness, which is modulated by the carbohydrates requirements of the colony. When fluid viscosity and ant morphometry remain constant, changes in intake rate could only be attributed to changes in sucking forces. Electrical records of this activity revealed two different signal patterns (Josens et al., 2006. J. Ins. Physiol. 52: 1234-1242): one is quite regular (RP) showing a sinusoidal type, whose frequency gradually decreases throughout the intake (5 to 2.5 Hz); the other is more irregular (IP) and presents higher frequencies (between 7 and 12 Hz). This study tries to enlighten the underlying mechanism of the intake rate modulation in ants. For that, ants proceeding of a colony with different carbohydrate starvation states were analysed during feeding on sucrose solutions of different concentrations. Behaviour and electrical activity were recorded by means of a non-invasive experimental device. The results have shown that ants can modulate the intake rate for a variety of solution concentrations (10%, 40% and 60% w/w). The IP did not occur during the intake of dilute solutions (10% and 40%) independently of the starvation. On the other hand, during the RP, higher signal frequencies were found beyond the values previously recorded reaching up to 7 Hz. The intake rate varied together with the pumping frequency -for a higher starvation state, higher frequencies and intake rates were obtained.  Besides, for concentrate solutions (60%) the IP occurred in relation with the nutritional state of the colony: the more starved the colony was, the more ants presented this pattern and the longer it appeared in each single intake. As the intake rate of concentrate solutions varied in the same direction as the IP, the relation between both variables was analysed. However, contrary to what could be expected, the presence of IP did not affect the intake rate, which is modulated in the same way as for dilute solutions, i.e. through frequency variations in pump activity during RP. So, each individual ant is able to change the pumping frequency according to the sugar requirements of the colony resulting in a modulation of the intake rate for a variety of solution concentrations.