Imported Fire Ants Discard Cricket Eggs

The house cricket, Acheta domesticus (Linnaeus), is often used as a food source for the maintenance of imported fire ants under laboratory rearing. It was found that both red imported fire ants, Solenopsis invicta Buren, and black imported fire ants, S. richteri Forel, consumed most of the soft tissues of female crickets, but avoided their eggs by disposing of them on refuse piles. Bioassays using freshly collected cricket eggs showed that ants first retrieved eggs into their nests and then discarded them onto the refuse piles. The major chemicals on the surface of cricket eggs were found to be fatty acids, including lauric, myristic, palmitoleic, palmitic, linoleic, oleic, and stearic acid. Fatty acids are well-known death cues of insects and elicitors of widespread necrophoric behavior in ants. It was shown that both the cricket egg extract and the reconstructed fatty acid mixture elicited the necrophoric behavior of S. invicta; however, they never elicited retrieving behavior. Unknown chemicals on cricket eggs, other than fatty acids, might be responsible for the retrieving behavior. Interestingly, cricket eggs had a very similar fatty acid profile to that of dead ants collected from refuse piles. Possible causes for such a strong match in fatty acid profiles between dead ants and cricket eggs are discussed.