Jean-Pierre Suzzoni

Ecdysteroid titre and caste determination in the ant,Pheidole pallidula (Nyl.) (Hymenoptera: Formicidae)

In the antPheidole pallidula, ecdysteroid level is higher in worker-biased eggs than queen-biased eggs. Moreover queens laying worker-biased eggs exhibit a higher ecdysteroid level than queens laying queen-biased eggs.

Surface Tension Strengths in the Service of a Ponerine Ant: a New Kind of Nectar Transport

cur during the passage of an egg through a honeybee queen’s reproductive tract? The fact that none of the control eggs in this study proceeded into embryonic development indicates that passage through the lateral oviducts alone is not sufficient to provide the appropriate mechanical distortions. Our histological study suggested that a more likely site where the distortions that activate embryonic development could occur is the central oviduct with its well-developed circular muscle. This would allow queens to store mature eggs in their lateral oviducts and produce viable haploid embryos by squeezing these eggs as they pass through the central oviduct on their way to the ovipositional pore. It appears, therefore, that in honeybees the central oviduct has taken over the role of mechanically stimulating unfertilized eggs that the ovipositor carries out in the Terebrantia. This was necessitated by a change in function of the ovipositor from an egg-laying role in Terebrantia to a stinging role in Aculeata. A mechanism of egg activation that did not rely on constriction at the ovipositor tip must have evolved in the Aculeata before or concurrent with this change of ovipositor function. The use of the circular muscle and narrow central ovident in honeybees might be one such mechanism. It remains to be seen whether the same or similar mechanisms are involved in other Aculeate species. The findings of such studies could have implications for the evolution of a stinging ovipositor and the divergence of the Aculeata from the Terebrantia.

BEHAVIORAL ADAPTATIONS OF AN AFRICAN PONERINE ANT IN THE CAPTURE OF MILLIPEDES

Workers of the ponerine ant Plectroctena minor are equipped with hypertrophied mandibles that can seize tubular millipedes, their essential prey, of up to 4 mm in diameter. We studied their predatory behavior in four situations where they captured spirostreptid millipedes. (1) P. minor workers generally seized millipedes of less than 4 mm in diameter dorsally and by their anterior part. During seizure the mandibles slipped on the exoskeletal coils of the millipede body and were caught between two segments that were slightly separated by the strong pressure. This facilitated stinging that mostly occurred ventrally in the soft intersegmentary space of the seized zone. (2) When a millipede was more than 4 mm in diameter, the workers seized it by an appendage before stinging or by wrapping themselves around the prey, then recruited nestmates in order to retrieve it. (3) The workers probably perceived kairomones from millipedes rolled into sloughing lodges as they opened the lodges and singly captured individuals less than 4 mm in diameter. Larger individuals (more than 4 mm in diameter) were captured after the workers recruited nestmates that generally cut up these prey on the spot. (4) When encountered in a test-tube simulating galleries, 95 to 105 mmlong millipedes (around 8 mm in diameter) were always captured. When the millipedes head was near the test-tube opening, the workers gripped the antennae or mandibles and stung the extreme anterior part of the millipede body, triggering rapid paralysis. In this case, they were even able to singly master then to retrieve these millipedes 94 to 117 times their weight, which represents the highest ratio for a solitary hunting strategy in ants. When the hind part of the millipede was near the test-tube opening, seizure was difficult and nestmates were recruited in most cases. We concluded that the behavioral flexibility of P.minor , which mainly occurred during the solitary phase of prey mastering, permitted the capture of millipedes of a wide range of sizes.

Selection and capture of prey in the African ponerine antPlectroctena minor (Hymenoptera: Formicidae)

Abstract Prey selection by Plectroctena minor workers is two-fold. During cafeteria experiments, the workers always selected millipedes, their essential prey, while alternative prey acceptance varied according to the taxa and the situation. Millipedes were seized by the anterior part of their body, stung, and retrieved by single workers that transported them between their legs. They were rarely snapped at, and never abandoned. When P. minor workers were confronted with alternative prey they behaved like generalist species: prey acceptance was inversely correlated to prey size. This was not the case vis-a-vis millipedes that they selected and captured although larger than compared alternative prey. The semi-specialised diet of P. minor permits the colonies to be easily provisioned by a few foraging workers as millipedes are rarely hunted by other predatory arthropods, while alternative prey abound, resulting in low competition pressure in both cases. Different traits characteristic of an adaptation to hunting millipedes were noted and compared with the capture of alternative prey. We also noted the parsimony of the behavioural phases during their capture compared to the capture of alternative prey.

Ecdysteroid production during caste differentiation in larvae of the ant, Plagiolepis pygmaea

ABSTRACT. Variations in ecdysteroids were measured by radio‐immunoassay in worker‐biased and queen‐biased larvae of the ant Plagiolepis pygmaea Latr. (Hymenoptera, Formicidae) during late larval development, i.e. from the end of winter diapause up to the prepupal period. At the end of diapause, larvae are bipotential and, depending on culture conditions, can become either queens or workers. Ecdysteroid profiles revealed that there are striking differences between the two castes: worker larvae showed high titres during their development, queen larvae had low titres over the same period.

Territorial aggressiveness and predation: two possible origins of snapping in the ant Plectroctena minor.

Plectroctena minor workers have long mandibles that can snap and deliver a sharp blow to intruders or prey, stunning or killing them. Encounters between homocolonial P. minor workers separated for 24 h or 15 days never resulted in snapping, while this behaviour was always noted during encounters between heterocolonial workers on neutral arenas or on the territory of a colony. In the latter case, only the aliens, that generally tried to escape, were snapped at. Snapping also occurred during encounters with workers belonging to sympatric ponerine species. During predation, the percentages of snapping varied according to prey nature, suggesting prey discrimination. Termite soldiers were always snapped at, while other prey were more often snapped close to rather than far from the nest entrances, indicating an intermingling of territorial aggressiveness and predatory behaviour. We discuss the adaptive value of snapping for hunting in galleries.