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The question of whether insects can perform concept learning or can use the geometry of space as in mammals has been recently addressed in Hymenoptera in an extensive way. We investigate here the ability of the tropical ant Gigantiops destructor to perform sequential learning and to use size relationships during navigation. Ants were trained to solve a dichotomic six-stage linear maze relying on the apparent width of two vertical landmarks. Each individual ant first learnt to associate a given landmark width to the motor decision of turning right or left to avoid dead-ends independently of a motor routine. When confronted for the first time with a new intermediate-sized pattern, for which no supposed snapshot could have been stored, ants made directional choices indicating that bar width judgments were not absolute but rather relative to the familiar visual patterns seen in the previous chambers. This result demonstrates that ants can generalize relationship rules by interpolating the relative width of a novel stimulus according to visual information kept in spatial working memory. In conclusion, ants can perform conditional discriminations reliably not only when stimuli are simultaneous but also when they are sequential. [ABSTRACT FROM AUTHOR]

Individual foraging ants are known to rely on views of their surroundings for route learning and for pinpointing goals. Different strategies have been proposed to explain how ants might process visual information for navigation, but little is known about the actual development and nature of the view-based strategies used by ants in complex natural environments. Here, we constrained the knowledge of Melophorus bagoti ants to either the nest vicinity or a curved route (length 10 m) and analysed their initial direction when released at both novel and familiar locations. In parallel, we used 360 deg pictures of the scene as a basis for modelling different navigational strategies. We propose here a new hypothesis based on skyline height comparison to explain how ants home from novel locations. Interestingly, this strategy succeeded well at novel locations but failed on familiar terrain. By contrast, the use of a visual compass strategy failed at novel locations but could explain the results on familiar routes. We suggest that ants might switch between skyline height comparison and a visual compass strategy, depending on whether they are on familiar terrain or not. How ants could switch between strategies and how their memories develop are discussed in turn. [ABSTRACT FROM AUTHOR]

The Australian desert ant Melophorus bagoti often follows stereotypical routes through a cluttered landscape containing both distant panoramic views and obstacles (plants) to navigate around. We created an artificial obstacle course for the ants between a feeder and their nest. Landmarks comprised natural objects in the landscape such as logs, branches, and tussocks. Many ants travelled stereotypical routes home through the obstacle course in training, threading repeatedly the same gaps in the landmarks. Manipulations altering the relations between the landmarks and the surrounding panorama, however, affected the routes in two major ways. Both interchanging the positions of landmarks (transpositions) and displacing the entire landmark set along with the starting position of the ants (translations) (1) reduced the stereotypicality of the route, and (2) increased turns and meanders during travel. The ants might have used the entire panorama in view-based travel, or the distal panorama might prime the identification and use of landmarks en route. Despite the large data set, both options (not mutually exclusive) remain viable. [ABSTRACT FROM AUTHOR]

Paltothyreus tarsatus workers show an adaptive predatory strategy compatible with central place theory which predicts that single-prey loading is an extension of the optimal diet choice while multiple-prey loading behavior would correspond to the optimal use of patches. The insight learning involved in the quick modifications of predatory strategy enables P. tarsatus to hunt all available prey in a great diversity of sizes and species. Nevertheless, this generalist predator strongly preferred termites and very large prey such as giant diplopods and crickets to other choices within its diet. In the hunting of these favorite prey, the recruitment of nestmates enhanced the efficiency of total predation, though the release of a chemical trail appeared to depend on the hunger-satiety balance of the colony. In addition to the hunger, the miscapture of prey also triggered the release of chemical trails. The strategy for capturing grouped termites was characterized by the loading of multiple prey at a single time, by a concentrated search in a restricted area and by an optional recruitment of nestmates. These behavioral characteristics of ponerine ants probably account for the flexibility of their predatory strategy for hunting aggregated small prey. [ABSTRACT FROM AUTHOR]

In this study we report a case of ant-trail following by lycaenid caterpillars. Euliphyra mirifica and E. leucyana caterpillars are involved in a commensal association with the weaver ant Oecophylla longinoda. The host nests are made with leaves which over the course of time dry out or are broken open by storms, forcing the ants to migrate and build a new nest elsewhere. Euliphyra caterpillars are stimulated by recruitment behaviour which triggers the migration of their host. They then follow the host trails leading to the new nesting site. Laboratory experiments showed that these caterpillars are able to follow host trails under varied conditions: (1) fresh trails actually used by workers, (2) fresh trails in the absence of workers, (3) heterocolonial, 2-month-old trails, and (4) fresh trails washed with water (to simulate the effect of tropical rains). They can also bridge trail gaps of more than 1 cm. Under natural conditions, the trails are frequently situated along thin twigs. The forward progress of the ants in such a situation is not impeded by the presence of large Euliphyra larvae. Workers just climb over the caterpillars, even on larger trails where there is enough room to pass alongside them. This suggests that an allomone is secreted on the dorsal part of the caterpillars. When crawling along heterocolonial trails, the caterpillars are not attacked, even if about 21% of the workers from the new colony spread their mandibles when encountering them. They are then adopted and are admitted to the nest of the new host colony of O. longinoda. [ABSTRACT FROM AUTHOR]

Ant parasitoidism has been reported in seven of the 26 recognized species of the mite genus Macrodinychus (Machrodynichidae). Macrodynichus sellnicki, previously reported as a parasitoid of the invasive ant Nylanderia fulva in Colombia, is now reported, in the same region, as attacking a native host, Ectatomma sp. 2 (E. ruidum complex). The mite develops within the protective silk cocoon of an Ectatomma pupa and waits for the emergence of the young ant before leaving the cocoon, unmolested. Overall nest prevalence was relatively high (34.6% of the 52 nests containing cocoons) but pupae prevalence was low (4.0%, n = 1401 cocoons). Mite life-history (parasite or parasitoid) was context dependent, shifting according to the intensity of the attack on a same host. Contrary to the strictly parasitoidic association of M. sellnicki with N. fulva, single mite attacks against E. ruidum did not result in host killing and solitary M. sellnicki (78.6% of the cases) behaved as parasites. However, in 21.4% of the attacks (0.9% of all available host pupae) more than one mite was involved and behaved as parasitoids, draining the host of its internal fluids and killing it. This is the first association of a macrodinychid mite with a species of the subfamily Ectatomminae, and the first ant associated mite for which such a context dependent life-style shift is described. [ABSTRACT FROM AUTHOR]