Occurrence of Wasmannia auropunctata (Hymenoptera: Formicidae) in forests of northern Argentina

L. CALCATERRA, J. BRIANO, F. CUEZZO, L. RAMÍREZ, P. FOLLET

Ouro Preto, Minas Gerais, Brasil

Simposio; XIX Simpósio de Mirmecologia e I Simpósio Franco-Brasileiro de Mirmecologia; 2009

                The Little Fire Ant (LFA), Wasmannia auropunctata, is native to South and Central America and has spread fairly recently around the Pacific. It is now a serious pest in archipelagos such as Hawaii and Galapagos, where infestations are disrupting agricultural practices and threatening wildlife. In October 2008, SABCL started a program to find natural enemies for their potential use in both archipelagos. Three field surveys were conducted in 38 sites in northern Argentina to search for LFA and natural enemies. Surveys were focused in three types of natural forests: 1) Yungas (little modified low mountain forest) in northwestern Argentina, 2) Paranaense (Atlantic semi-evergreen moist forest) in northeastern Argentina and 3) Chaco/Espinal (mostly gallery forest) in central northern Argentina. A total of 665 samples of ants were obtained using sieves (6 per site in average) and baits (14 per site in average); 146 plots (0.25-m2) were sampled: 55 in Yungas, 46 in Paranaense, and 45 in Chaco/Espinal. The leaf litter of each plot was collected and sieved (1x1 cm) to a white plastic tray. Ants were collected with forceps and kept in 96% alcohol for their identification. Baits (1-2g of canned tuna on paper cards) were exposed for 45 min. In each site, baits were placed on the ground every 10-20m along a 200-m transect. Ants were attracted to a total of 519 baits: 164 in Yungas, 172 in Chaco/Espinal, and 183 baits in Paranaense. A total of 98 species was found in the Paranaense, 67 in Chaco/Espinal, and 55 in the Yungas; however, the mean number of species per sample was similar in the 3 regions. Wasmannia auropunctata was found up to 34º13´ south latitude and between 45 and 750 m of altitude. The presence of the LFA was 3 times higher in the Chaco/Espinal, occurring in 8 (72.7%) of the 11 sites. The LFA was 3-5 times more abundant in the Chaco/Espinal, being found in 25 (11.4%) of the 220 samples. Other Wasmannia spp. occurred with LFA: 1) Wasmannia sp. 1 was found for the first time in Argentina in the Chaco/Espinal. This non-described species is similar to that reported by Alex Wild (Wasmannia cf. alw01) for Paraguay; 2) Wasmannia sulcaticeps was found in the Yungas at 690-750 m of altitude; it co-occurred with W. auropunctata only in Calilegua at 750 m of altitude; 3) Wasmannia cf. rochai was found also for the first time in Argentina in the Paranaense at 192-243 m of altitude, but it did not co-occur with the LFA. So far, natural enemies were not found. Alarm pheromones are being used to improve the search of LFA colonies in the field.