Abdominal Trophallaxis in the Slave-Making Ant, Harpagoxenus Americanus (Hymenoptera: Formicidae)

Abdominal trophallaxis refers to the passage of fluids from t h e abdominal tip of one individual to the mouthparts of another. I t is common among lower termites (Kalotermitidae and Rhinotermitidae) where it functions in the vital transmission of intest inal flagellates to newly molted individuals. However, it has rarely b e e n documented among ants (Wilson, 1971, 1976). By strict definition, the term abdominal trophallaxis should be applied only w h e n alimentary fluid is being transmitted (Wilson, 1971). Nevertheless, in practice, the origin of the fluid is often unknown, at least initially. Indeed, in all cases where this behavior has been described in a n t s , the fluid is either suspected of being, or has since been shown to be, ovarian in nature. For example, workers of certain Eciton spec ies (Dorylinae) readily feed from droplets secreted from the tip of t h e queen's abdomen, but this behavior has been observed only d u r i n g egg-laying bouts (Schneirla, 1944; Rettenmeyer, 1963). So-called "proctodeal feeding" has also been described among the Dol i choderinae (Dolichoderus quadripunctatus, Tapinoma erraticurn and Iridomyrmex humilis) (Torossian, 1958, 1959, 1960, 1961 ). However, at least in the case of D. quadripunctatus, the fluid h a s been identified as the yolky remnants of abortive trophic e g g s (Torossian, 1978, 1979). Among the Myrmicinae, Zacryptocerus varians exhibits a similar behavior which is also thought to be associated with egg-laying (Wilson, 1976). This paper reports an unusual and interesting case of abdominal trophallaxis in colonies of the socially parasitic myrmicine ant, Harpagoxenus americanus. 1 have followed Wilson (1976) and tentatively applied the t e r m abdominal trophallaxis, because the origin of the fluid is unknown. H. americanus is an obligatory slave-maker and forms m i x e d colonies with members of certain Leptothorax species in ea s t e rn