Pheromonal and behavioral queen control over the production of gynes in the Argentine ant Iridomyrmex humilis (Mayr)

Abstract

Both field observations and laboratory experiments have suggested that queens of I. humilis inhibit the production of new queens (gynes). Using small colony fragments, laboratory experiments were conducted to determine the means by which this inhibition is achieved. The addition of queen corpses to queenless fragments effectively inhibited the production of gynes, suggesting that a queen inhibitory primer pheromone is involved. This inhibitory influence was removed when corpses were washed in pentane, lending further support to the pheromonal hypothesis. Adult gynes (winged virgin queens) were not inhibitory, whereas young dealated mated queens of the same age were, suggesting that only inseminated queens produce the pheromone. Daily addition of eggs to queenless units did not appear to have a strong inhibitory influence, indicating that the lower worker/larva ratios associated with the presence of an egg-laying queen in such colony fragments does not greatly influence the production of sexuals. Pheromonal inhibition of gyne development appears to be achieved mainly by preventing the sexualization of bipotent female larvae, probably by affecting the brood-rearing behavior of workers. In addition, queens may also cause the execution of female larvae after they have become sexualized. In nearly all cases, the addition of a living queen to previously queenless units containing gyne larvae caused workers to execute one or more of these larvae within 24 h. In some cases queens were also seen attacking gyne larvae. The addition of queen corpses resulted in the execution of gyne larvae, suggesting that a queen pheromone mediates, at least in part, this execution behavior of workers. These results show that I. humiIis queens exert control over the production of gynes in two ways: (1) by preventing the sexualization of female larvae and (2) by killing female larvae after they have become sexualized. A queen primer phero-* Present address: mone appears to be involved in both processes. Queen behavior also plays a role, at least in the execution of gyne larvae. This queen control over the production of gynes, probably mostly pheromonal, appears to operate strongly in the field where gynes are produced only in spring just after a sharp drop in the inhibitory queen influence due to the massive execution of queens by the workers.

Production of sexuals in a fission-performing ant: dual effects of queen pheromones and colony size

“…We can exclude the possibility of worker thelytoky, which has been suggested as a possible mode of gyne production in QL colonies of A. senilis (Ledoux 1984), because this required a thermal shock to which our lab colonies were not submitted. This suggests that under QR conditions, the queen inhibits diploid brood determination to gynes either directly or by affecting worker care behavior towards these larvae (Wilson 1971;Brian 1973;Vargo and Passera 1991;Wheeler 1994).…”

“…The queen may directly affect larval physiology, or she may inhibit gyne production indirectly by modifying worker behavior. Hence, apart from a few notable cases of maternal effect (de Menten et al 2005) or genetic control (Julian et al 2002;Volny and Gordon 2002), the differentiation between gynes and workers seems to occur at the larval stage and depend on the type of care provided by the nurses (Wilson 1971;Brian 1973;Vargo and Passera 1991;Wheeler 1994). In addition, while workers of many species have retained functional ovaries and could increase the colony reproductive allocation by laying their own male eggs, other constraints (worker-worker conflicts over male parentage and colony-level selection) generally prevent them from doing so under queenright (QR) conditions (Woyciechowski and Łomnicki 1987;Ratnieks 1988;Hammond and Keller 2004).…”

Sex Ratio Conflict and Worker Production in Eusocial Hymenoptera

“…Workers of some Myrmica species have for instance been reported to provide less food to overwintering than to spring larvae (Brian 1983). Aggression toward larvae developing into gynes has been reported in several ant species (Fletcher 1986;Vargo and Passera 1991). The differential treatment of gyne-inclined larvae by workers may represent means to incite larvae to develop into workers.…”

Power over reproduction in social Hymenoptera

“…However, access to brood also gives the adult workers more power. In several polygynous ant species, workers starve, attack or cannibalize queenpotential larvae (Brian 1973;Vargo & Fletcher 1986a,b;Edwards 1987Edwards , 1991Keller et al 1989;Vargo & Passera 1991;Keller & Passera 1992). This either leads to the larvae being killed, or it may cause them to develop into workers rather than queens (Bourke & Ratnieks 1999).…”