USE OF STRIDULATION IN FORAGING LEAF-CUTTING ANTS - MECHANICAL SUPPORT DURING CUTTING OR SHORT-RANGE RECRUITMENT SIGNAL

Foraging leaf-cutting ant workers stridulate while cutting a leaf frag ment. Two effects of stridulation have recently been identified: (i) a ttraction of nestmates to the cutting site, employing substrate-borne stridulatory vibrations as short-range recruitment signals, and (ii) m echanical facilitation of the cut via a vibratome-effect. We asked whe ther foragers actually stridulate to support their cutting behavior, o r whether the mechanical facilitation is an epiphenomenon correlated w ith the use of stridulation as recruitment signal. To differentiate be tween the two alternatives, workers of two different Atta species were presented with tender leaves of invariant physical traits, and their motivation to initiate recruitment was manipulated by varying the pala tability of the leaves and the starvation of the colony. The lower the palatability of the harvested leaves, the lower the percentage of wor kers that stridulated while cutting, irrespective of the leaf's physic al features. After intense feeding, no workers were observed to stridu late while cutting tender leaves, and the percentage of stridulating w orkers increased with deprivation time. The results support the hypoth esis that leaf-cutting ant workers stridulate during cutting in order to recruit nestmates, and that the observed mechanical facilitation of stridulation is an epiphenomenon of recruitment communication.