Venom alkaloids of fire ants in relation to worker size and age.

Piperidine alkaloids compose most of the venom of the red imported fire ant, Solenopsis invicta, and we examined how six of these alkaloids varied across worker size and age. In a colony sampled intensively, the relative abundance of each alkaloid was highly correlated with worker size with one exception, and ratios of saturated to unsaturated alkaloids were positively correlated with worker size. Similarly, both the abundance and ratios of alkaloids differed significantly between the small and large workers sampled from colonies across Texas, USA. Young and old workers produced less venom than ants of intermediate age (3-7 weeks), and ratios of saturated to unsaturated alkaloids increased significantly with worker age. The differences in venom composition correspond to the size- and age-based functional roles of workers.