Interactions of the invasive Linepithema humile and honeydew-producing Hemiptera

Abstract

We investigated the importance of honeydew to the Argentine ant in an infestation in Raleigh, North Carolina, during the summer and winter months. Within this infestation there was a facultative mutualism between the Argentine ant and the endemic terrapin scale on red maples prevalent during the warmer moths. This mutualism had an indirect cost to the host tree with smaller seeds and leaves on Argentine ant infested red maple. When Argentine ants were excluded from trees, terrapin scale populations collapsed and local Argentine ant nests relocated away from excluded trees. We investigated the effect honeydew denial would have on boric acid consumption. Bait consumption was lower where honeydew access denied. We attribute this to longer distances reducing foraging effort of Argentine ant colonies.

It was unknown if Argentine ants could overwinter without feeding or whether continuous feeding is required even in North Carolina’s harsh winters. We maintained Argentine ant nests at 4oC, below minimum foraging limits but above freezing. Even in the presence of protein and carbohydrates Argentine ant nests failed after a few weeks, indicating that Argentine ant cannot survive extended periods without foraging. Argentine ants had been observed trailing on loblolly pine even when temperatures were below minimum foraging limits. We measured the bark temperature of loblolly pine during the winter months. Even when ambient temperatures were below minimum foraging limits the bark solar radiation could heat the bark to temperatures that were within the optimal foraging range of the Argentine ants. We compared the weights of Argentine ant workers trailing up the pine trunk to those trailing down. We found that workers trailing down the trunk were heavier than those trailing up indicating that the Argentine ants are feeding on a liquid food source, probably honeydew. Argentine ants are known to aggregate into big winter colonies and we showed that Argentine ant winter colonies aggregate around loblolly pines. We believe that this aggregation is not to escape cold temperatures but to concentrate around a reliable winter food source.