Climate Change Impact on Neotropical Social Wasps

Establishing a direct link between climate change and fluctuations in animal populations through long-term monitoring is difficult given the paucity of baseline data. We hypothesized that social wasps are sensitive to climatic variations, and thus studied the impact of ENSO events on social wasp populations in French Guiana. We noted that during the 2000 La Niña year there was a 77.1% decrease in their nest abundance along ca. 5 km of forest edges, and that 70.5% of the species were no longer present. Two simultaneous 13-year surveys (1997–2009) confirmed the decrease in social wasps during La Niña years (2000 and 2006), while an increase occurred during the 2009 El Niño year. A 30-year weather survey showed that these phenomena corresponded to particularly high levels of rainfall, and that temperature, humidity and global solar radiation were correlated with rainfall. Using the Self-Organizing Map algorithm, we show that heavy rainfall during an entire rainy season has a negative impact on social wasps. Strong contrasts in rainfall between the dry season and the short rainy season exacerbate this effect. Social wasp populations never recovered to their pre-2000 levels. This is probably because these conditions occurred over four years; heavy rainfall during the major rainy seasons during four other years also had a detrimental effect. On the contrary, low levels of rainfall during the major rainy season in 2009 spurred an increase in social wasp populations. We conclude that recent climatic changes have likely resulted in fewer social wasp colonies because they have lowered the wasps' resistance to parasitoids and pathogens. These results imply that Neotropical social wasps can be regarded as bio-indicators because they highlight the impact of climatic changes not yet perceptible in plants and other animals

Questioning the implementation of habitat corridors: a case study in interior São Paulo using ants as bioindicators

In this paper we operated ant collections in three inland Atlantic forest fragments and in the neighboring Edmundo Navarro de Andrade State Forest (FEENA), an Eucalyptus plantation located in Rio Claro, interior of São Paulo State. We show that the ant communities of the native forest fragments are more similar among themselves than to the ant community of FEENA. Thus we evidence that, in addition to the clear difference in vegetation segment, other components of the biota (like ants) can be different between FEENA and the native forest fragments. Our results conveniently served as a basis to discuss the proposal of connecting FEENA to the three native forest fragments by a habitat corridor. These fragments are important to conservation purposes since they represent the biggest areas of native vegetation in the region

Queen Specific Exocrine Glands in Legionary Ants and Their Possible Function in Sexual Selection.

The colonies of army ants and some other legionary ant species have single, permanently wingless queens with massive post petioles and large gasters. Such highly modified queens are called dichthadiigynes. This paper presents the unusually rich exocrine gland endowment of dichthadiigynes, which is not found in queens of other ant species. It has been suggested these kinds of glands produce secretions that attract and maintain worker retinues around queens, especially during migration. However, large worker retinues also occur in non-legionary species whose queens do not have such an exuberance of exocrine glands. We argue and present evidence in support of our previously proposed hypothesis that the enormous outfit of exocrine glands found in dichthadiigynes is due to sexual selection mediated by workers as the main selecting agents

Combined use of pheromone trails and visual landmarks by the common garden ant Lasius niger

This study investigated the relative importance of pheromone trails and visual landmarks on the ability of Lasius niger foragers to relocate a previously used food source. Colonies formed foraging trails to a 1-M sucrose feeder. Sections of this trail were then presented back to the same colony after variable time intervals. Individual outgoing foragers were observed to determine if they walked for 15 cm in the direction of the feeder or not. On newly established pheromone trails formed by 500 ant passages, 77% of the foragers walked in the correct direction vs 31% for control foragers ( no trail pheromone). Pheromone trails decayed to the control levels in 20-24 h. Trails formed with fewer ant passages ( 125 or 30) decayed quicker. The use of visual landmarks was investigated by using trails with outgoing foragers from the colony that established the trail, either in the same room or in a different room, with different visual landmarks, to that used during trail establishment. Approximately 20% more ants walked in the correct direction in the same room vs the different room. This difference decreased to around 10% 2 h after trail establishment, indicating that the ants in the different room were learning the new visual cues to navigate by. Our results show that visual landmarks and pheromone trails are approximately equally useful in initially guiding L. niger foragers to food locations and that these two information sources have a complementary function