Foraging trail traffic rules: a new study method of trajectories of the harvester ants.

Harvester ants are one of the most extensively studied groups of ants, especially the group foraging ants, Messor barbarus (Linnaeus, 1767), which construct long-lasting trunk trails. Limited laboratory investigations have delved into head-on encounters along foraging trails involving workers moving in opposing directions, with fewer corresponding studies conducted in the natural environment. To address this gap, we devised an in-field experimental design to induce lane segregation on the foraging trunk trail of M. barbarus. Using an image-based tracking method, we analyzed the foraging behavior of this species to assess the costs associated with head-on encounters and to figure out the natural coexistence of outgoing and returning workers on a bidirectional route. Our results consistently reveal heightened straightness and speed in unidirectional test lanes, accompanied by an elevated foraging rate compared to bidirectional lanes. This suggests a potential impact of head-on collisions on foraging behavior, especially on foraging efficiency. Additionally, Kinematic analysis revealed distinct movement patterns between outbound and inbound flows, particularly low speed and sinuous trajectories of inbounding unladen workers. The study of encounter rates in two traffic systems hints at the plausible utilization of individual memory by workers within trails, underscoring the pivotal role of encounters in information exchange and load transfer.

Context-dependent insect predation pressure on an avian ectoparasite.

Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host-parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.

Five new records of ants (Hymenoptera: Formicidae) from Morocco.

A recent catalogue of the rich ant fauna of Morocco included 214 species, with later studies adding an additional 12 species. Following recent fieldwork in the north of Morocco, we report five new records for the country (Plagiolepis pygmaea Latreille, 1798, Ponera testacea Emery, 1895, Strumigenys tenuipilis Emery, 1915, Temnothorax pardoi Tinaut, 1987, and Tetramorium parvioculum Guillem & Bensusan, 2009) and we present new data on the distribution and natural history of six additional species. This work brings the total number of ants known from Morocco to 233, taking into account two species which were omitted in the list of Cagniant.

Foraging strategy quick response to temperature of Messor barbarus (Hymenoptera: Formicidae) in Mediterranean environments.

Animals principally forage to try to maximize energy intake per unit of feeding time, developing different foraging strategies. Temperature effects on foraging have been observed in diverse ant species; these effects are limited to the duration of foraging or the number of foragers involved. The harvester ant Messor barbarus L. 1767 has a specialized foraging strategy that consists in the formation of worker trails. Because of the high permeability of their body integument, we presume that the length, shape, and type of foraging trails of M. barbarus must be affected by temperature conditions. From mid-June to mid-August 1999, we tested the effect on these trail characteristics in a Mediterranean forest. We found that thermal stress force ants to use a foraging pattern based on the variation of the workers trail structure. Ants exploit earlier well-known sources using long physical trails, but as temperatures increases throughout the morning, foragers reduce the length of the foraging column gradually, looking for alternative food sources in nonphysical trails. This study shows that animal forage can be highly adaptable and versatile in environments with high daily variations.