BIOLOGY  (for more information:  Espadaler, X. Bernal, V. i Rojo, M. 2006b.)

Many European authors describe Lasius brunneus as a timid species, adapted to life in old or dying trees and relatively frequent in Europe (Bernard, 1968; Collingwood, 1979; Kutter, 1977; Seifert, 1992). Nevertheless, although the genus Lasius, in general, is one of most abundant and common in the holarctic region, its general biology is poorly known. Strictly arboreal, Lasius brunneus usually nests under the bark in old, mainly deciduous trees. It has been found in oak, elm, beech, poplar, willow, majuelo and maple (Donisthorpe, 1927), and also in chestnut, linden and cork-oak. They can be present both in the tree, and in the ground at its base or under nearby stones.

  • Annual activity. In the studied plots in the forests of Sant Hilari Sacalm the activity throughout the year of Lasius brunneus shows similar trends to those of the majority of Mediterranean ants. Activity was detected from the month of March in all trees. In August and September there is a reduction in activity, probably because of the much lower air humidity and high temperatures. During the winter, activity is nil and this lasts for three months. Thus, its activity rhythm is no different from that of other native species. Following a period of building body reserves they go into hibernation during the colder months (Bonaric, 1971).

  • Food and feeding habits

- Ants may have a system of accumulation of reserves in the gaster, the fat body. This reserve is accumulated when winter approaches and is consumed when, in spring, normal colony activity resumes. In Lasius brunneus the evolution of the amount of fat body is similar to that in other native species, in which it is consumed completely by early June. From that moment the workers are forced to find external food sources. This provides a convenient window of time for the application of bait-based treatments.

- Food supply. The presence of the aphid Stomaphis quercus  (L.) has been observed under cork, during the months of March to May. Stomaphis quercus has been reported in the Iberian Peninsula on Quercus rotundifolia. In other places in Europe, this rare big aphid is known on oaks: Q. robur, Q. petrea and, exceptionally, in Alnus glutinosa and Betula pendula (Grandson et al., 2002). It is currently being surveyed in the U.K. (Aphid survey.pdf). Cork-oak was previously unknown as a host for this aphid. Observations in England demonstrate the relationship of this aphid with Lasius brunneus (Pontin, 1983). Since the aphid has been found in many of the studied sites in Catalonia, it is doubtless that the honeydew excreted constitutes a continuous food source from March onwards. It is not known if it is the most important food source for Lasius brunneus or, perhaps, the sole one.

- When considering a possible treatment with poisoned baits, an important fact, besides knowing the number of individuals in a colony, is the volume of liquid that a worker can ingest. Through laboratory tests we got a mean of 0,27 Ál per worker. Accepting as a rough estimate of mean worker number per colony that known for other species of Lasius (10,000 workers), and assuming that the global food consumption for brood is similar to that of adult workers, the quantity of bait to offer to a colony (brood + workers) is about 5 cc.

  • Another important aspect for its control, is to know whether the workers of Lasius brunneus are able to reconstitute the society were the queen to be eliminated. Tests in the laboratory with artificial nests, demonstrate that the workers of Lasius brunneus are sterile, so that a possible treatment that could kill the queen, would also finish, in the long run, with the whole society. However, although doubtful because of monogyny, the possibility of queen adoption on the part of an orphaned society cannot be completely discarded (Collingwood, 1979).

  • Location of the colony in the tree. Although it is certain that higher activity occurs in the north-oriented zones of the tree, the general location of the society within the tree is diffuse. The queen and the main body of the society are located in the non-exploited part of the cork.

 


Page authors: Xavier Espadaler  (Xavier.Espadaler@uab.es) and VÝctor Bernal (v.bernal@creaf.uab.es).