Imported fire ants discard cricket eggs

Authors: Chen, Jian; Ni, Xinzhi; Grodowitz, Michael

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2024
Publication Date: 11/28/2024
Citation: Chen, J., Ni, X., Grodowitz, M.J. 2024. Imported fire ants discard cricket eggs. Insects. 2024, 15, 954.

Interpretive Summary: During routine feeding of crickets to laboratory imported fire ant colonies it was observed that while most of the cricket tissues are used by the fire ants only the hard outside shell or cuticle and the eggs are not utilized. Interestingly, the eggs are removed from the nest and deposited in refuse piles created by the fire ants. Why waste a highly nutritious food source such as cricket eggs? It was found though several experimental trials and chemical analyses that the surface of the cricket eggs have a chemical profile consisting mainly of fatty acids like that found on dead fire ants and as such elicits what is known as necrophoric behavior where chemical cues on the surface of the ants elicited a behavior where the dead ants are removed from the colony and deposited in refuse piles. Possible reasons for such similar surface composition between fire ants and cricket eggs are discussed.

Technical Abstract: 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 its eggs by disposing them in refuse piles. Bioassays using freshly collected cricket eggs showed that ants first retrieved eggs into their nest and then discarded eggs into the refuse piles. The major chemicals on the surface of cricket eggs were found to be fatty acids, including lauric acid, miristic acid, palmitoleic acid, palmitic acid, linoleic acid, oleic acid and stearic acid. Fatty acids are well known death cues of insects and elicitor of widespread necrophoric behavior in ants. It was shown that both 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 as that of dead ants collected from refuse piles. Possible causes for such a close match in fatty acid profiles between dead ants and cricket eggs are discussed.