Increasing attractiveness of baits with venom gland extract for Atta sexdens rubropilosa (Forel) (Hymenoptera: Formicidae).

The effect of larval cuticle extract (larval pheromone) and venom gland extract (trail pheromone) on transport of formulated baits by Atta sexdens rubropilosa (Forel) was studied in the field and under laboratory conditions. In the laboratory, we observed the transport to the nest of baits impregnated with 10 µL of venom gland extract (0.01 gland/bait) or 10 µL of larval cuticle extract (0.05 larva/bait). The most transported impregnated bait was then tested in the field placing rubber septa impregnated with 100 mL of extract or with 100 mL of solvent with the baits at 0.2, 1.0, 5.0, and 10.0 m away from the trail and from the nest entrance. Baits impregnated with venom gland extract were transported more often than baits formulated with larval cuticle extract. In field tests, the venom gland extract reduced the time required for ants to detect baits and increased the transport of baits displayed at 0.2 m from the foraging trail or nest entrance. The increase in the transport of impregnated baits and the lower time to be transported might help to reduce the loss of bait in the field and decrease the risk of active ingredient contacts with non-target species.

Resource allocation among worker castes of the leaf-cutting ants Acromyrmex subterraneus subterraneus through trophallaxis.

The division of labor between the different worker castes of leaf-cutting ants may reflect in their capacity to exchange liquids by trophallaxis. The crop capacity of and trophallactic exchanges between different size classes of worker leaf-cutting ants of the sub-species Acromyrmex subterraneus subterraneus were investigated. Size classes were defined from head capsule widths and crop capacity of each class was determined following ad libitum feeding on dye solution. Experiments were carried out to investigate trophallactic exchanges between donor ants and recipient ants of each class size combination on a one to one basis. An experiment was also performed to investigate dye distribution within mini-colonies following introduction of three classes of donor ants. Worker ants were categorized into four size classes from their head capsule widths (C1=0.8-1.0 mm; C2=1.2-1.5 mm; C3=1.6-2.0 mm; C4=2.1-2.4 mm). C1 ants crop capacity was 0.13 microL; C2: 0.21 microL; C3: 0.52 microL; C4: 1.03 microL. Ants of each class previously fed on the dye solution (donors) were placed individually with an unfed ant of each class (recipients) and the presence of dye solution, passed from the donor to the recipient by oral trophallaxis was observed after 1h. Results showed that all classes of donor ants performed trophallactic exchanges with all recipient classes. However, statistically fewer exchanges were seen for C2 donor ants when placed with C3 recipient ants. Ten donor ants of each of three classes (C2, C3 and C4) were introduced into mini-colonies without queen ants. It was observed that C1 and C2 ants were poor recipients, whilst C3 and C4 received the highest percentages of dye. Within 10h of introducing the donor ants, 14 to 20% of their nest-mates had received dye solution, with 58 to 77% of dye passed to recipients. These studies show the altruistic nature of "food-laden" leaf-cutters and indicate that ants involved in garden maintenance activity are less likely to receive liquids from foraging workers.

Survey of Neodohrniphora spp. (Diptera: Phoridae) at colonies of Atta sexdens rubropilosa (FOREL) and specificity of attack behaviour in relation to their hosts.

Atta sexdens rubropilosa is a leaf-cutting ant that is a significant agricultural and forestry pest in the Neotropical region. This ant is parasitized by flies from the genera Neodohrniphora spp., Apocephalus spp. and Myrmosicarius spp. This study was carried out to determine which species of Neodohrniphora spp. are found near foraging trails of Atta sexdens rubropilosa and to evaluate the specificity of attack behaviour of these parasitoids. From May 2002 to April 2004, we sampled Neodohrniphora spp. hovering over foraging trails of Atta sexdens rubropilosa between 8:00 and 11:00 h and between 15:00 and 18:00 h. To investigate the attacking behaviour against the ants, flies were released individually inside an observation chamber containing a single leaf-cutting ant worker. Each parasitoid was confronted successively with a worker ant of A. sexdens rubropilosa, Atta laevigata Smith, Acromyrmex crassispinus Forel and Acromyrmex subterraneus molestans Santschi. Phorids of three species were identified: Neodohrniphora elongata Brown, Neodohrniphora declinata Borgmeier and Neodohrniphora tonhascai Brown. The three phorid species were active throughout the year and often along the same foraging trails, but N. elongata was the most frequent species. In the laboratory assay, N. elongata, N. declinata and N. tonhascai attacked workers of A. sexdens rubropilosa, A. laevigata and A. crassispinus, but not of A. subterraneus molestans.