Howard Topoff

Avoiding predation by army ants: Defensive behaviours of three ant species of the genus Camponotus

Abstract Antipredation behaviours of three ant species of the genus Camponotus were investigated in field and laboratory studies. Contact with the army ant Neivamyrmex nigrescens was shown to produce nest evacuation and removal of brood by colonies of Camponotus festinatus . Colonies of Camponotus ocreatus and Camponotus vicinus defended their nests through recruitment of the major caste. The initiation of evacuation or aggressive recruitment was dependent upon tactile contacts between Camponotus nestmates. Other sorts of disturbance which did not involve army ant contact did not produce evacuation or recruitment, indicating a high degree of enemy specification by Camponotus . The comparison of worker morphology revealed a close relationship between each species strategy for nest defence and the degree of worker polymorphism exhibited. These findings suggest that interspecific ant predation has been a significant factor in the evolution of colony defence systems and caste polymorphism.

Colony takeover by a socially parasitic ant, Polyergus breviceps : the role of chemicals obtained during host-queen killing

Abstract Abstract. The behavioural adaptations of parasitic ant queens are more complex than those of parasitic birds, in which the egg-laying female approaches the nest only when the host parents are absent, and leaves immediately after egg deposition. Queens of the socially parasitic ant Polyergus breviceps are incapable of rearing their own brood, and therefore require the assistance of host Formica workers soon after egg laying. Accordingly, a newly mated Polyergus queen must penetrate a nest of Formica, kill the host queen, and become permanently accepted by the slave species workers. Laboratory tests show that a Polyergus queen will similarly attack and bite a dead (and therefore motionless) Formica queen. Immediately after attacking the dead host queen, the Polyergus queen will be accepted by workers from any colony of Formica belonging to the same species of the dead queen (but will be attacked by workers from other Formica species). Preliminary results also indicate that any adoption-facilitating chemicals obtained by the Polyergus queen are still effective 1 week after killing the host Formica queen. When Polyergus queens raised in colonies containing F. gnava were introduced into nests of F. occulta, most showed little interest in attacking the resident Formica queen. In four of 10 tests, however, the Polyergus queen killed the foreign queen and was accepted by the F. occulta workers. Such chemical transfer of foreign-queen odours may have played a key role in the evolution of social parasitism in Polyergus.

Behavioural ecology of mass recruitment in the army ant Neivamyrmex nigrescens.

The successful rearing of the army ant Neivamyrmex nigrescens in the laboratory has enabled us to demonstrate that the pheromone trail deposited by recruiting workers is qualitatively different from the ants exploratory trail. The recruitment trail alone can initiate as strong a mass recruitment response as can a recruiting worker that physically interacts with nestmates. The rapidity with which workers are aroused is due to secondary recruitment. Army ants are able to assemble a critical striking force before food is located, as a result of mass recruitment to new terrain. In addition to feeding behaviour, mass recruitment occurs when army ants emigrate to new nests. In both behavioural contexts, primary and secondary recruiters run more rapidly than exploring ants, and with exaggerated vertical motor patterns.

Army Ants on the Move: Relation Between Food Supply and Emigration Frequency

Underfed colonies of Neivamyrmex nigrescens in the laboratory emigrated on 62 percent of the nomadic days, as compared with only 28 percent for overfed colonies. Because the emigration frequency in the field is similar to that of underfed colonies, nomadic raids may not bring in enough food to satiate the larval broods. Since emigrations take time away from raiding, the food-related mechanism underlying emigrations may have evolved under more stringent ecological conditions.

Queen Sex Pheromone of the Slave-making Ant, Polyergus breviceps

Workers of the slave-making ant, Polyergus breviceps, raid nests of Formica ants and return with Formica pupae that mature into worker ants in the slave-makers’ colony. These Formica workers then tend the Polyergus brood, workers, and reproductives. During raids in the mating season, winged virgin Polyergus queens accompany the workers in the raiding columns. During the raid, the virgin queens release a pheromone that attracts males that quickly mate with the queens. We report the identification, synthesis, and bioassay of the sex attractant pheromone of the queens as an approximately 1:6 ratio of (R)-3-ethyl-4-methylpentan-1-ol and methyl 6-methylsalicylate. The ants produce exclusively the (R)-enantiomer of the alcohol, and the (S)-enantiomer has no biological activity, neither inhibiting nor increasing attraction to blends of methyl 6-methylsalicylate with the (R)-enantiomer.

Orientation of the army ant neivamyrmex nigrescens: Integration of chemical and tactile information

Abstract The success of the large-scale raids and emigrations of the army ant Neivamyrmex nigrescens (Cresson) depends upon their ability to orientate by responding to a chemical trail and to tactile stimuli provided by physical objects. Laboratory experiments showed that the workers response to tactile stimuli increases in the absence of a chemical trail. Under these conditions, test ants behave much as they do in the field at a raiding front. This may explain why raiding columns are typically established along the base of rocks, fallen tree trunks, and other inanimate objects. Other experiments show that tactile stimuli may, in turn, facilitate the ants orientation to weak chemical trails.

Precocial behaviour of callow workers of the army ant Neivamyrmex nigrescens: Importance of stimulation by adults during mass recruitment

Abstract Callows of the army ant Neivamyrmex nigrescens do not participate in predatory raids until 3 to 7 days after their eclpsion. Within 24 h after their eclosion, however, the entire callow population joins with the adult ants in emigrating to a new nesting site. This emigration is accomplished by mass recruitment of the callows by the mature adult workers. Tests show that adults use mechanical stimulation to arouse callows to trail-following. Callows remain in the nest during raiding because their central location effectively sequesters them from the excitatory effects of the adult workers. The early participation of callows in the predatory raids suggests a precocial development that might have evolved as an adaptation for group predation and nomadic emigrations.

Army ants do not eat and run: influence of food supply on emigration behaviour in Neivamyrmex nigrescens.

Abstract Laboratory studies show that the amount and location of food strongly influence the frequency and direction of emigrations. For two overfed colonies, emigrations occurred on only 28% of the nomadic days. By contrast, underfed colonies emigrated on 62% of the nomadic days. In addition, overfeeding kept one colony from emigrating for seven consecutive days, as compared with a maximum of two consecutive days for the underfed colonies. Most emigrations took place in the direction of booty location. It was shown, however, that colonies can also recruit and emigrate to suitable nests, independent of the presence of food.

A comparison of trail following between callow and adult workers of the army ant [Neivamyrmex nigrescens (Formicidae: Dorylinae)]

Abstract Although newly emerged (callow) army ants emigrate along with their colony on the first nomadic night, they remain in the nest and do not participate in raiding until they are several days old. In tests comparing trail following of callow and adult workers of Neivamyrmex nigrescens on an artificial trail, the callows performed as well as or better than the adults. Because we can no longer attribute the absence of callows from raiding columns to their inability to follow the trail, we hypothesize that the callows remain in the nest because they are extremely sensitive to the chemical (and tactual) stimuli that are most intense inside the nest.

Social Organization of Raiding and Emigrations in Army Ants

Publisher Summary The chapter discusses the results of field and laboratory research on the relationship between food supply and emigrations, on chemical communication and orientation, and on other behavioral processes that relate to brood stimulation theory. The goal of these studies is to understand how processes occurring inside the nest interact with factors in the colonys external environment in influencing differences in colony behavior between the nomadic and statary phases, as well as behavioral variations within each phase. The chapter discusses army ants in perspective by briefly reviewing their evolution and taxonomic status. Army ants comprise approximately 300 species of tropical and subtropical ants, whose behavior is uniquely characterized by the combination of group predation and nomadism. The two behavioral characteristics of army ants, group predation and nomadism, well known to many of the early naturalists, and usually postulated food exhaustion as the proximate cause of the ants periodic emigrations. By emphasizing the process of recruitment, raid site location, food supplies, and other factors whose primary influence takes place outside of the bivouac, this chapter extends and not replaces, Schneirlas concept of army ant social organization.