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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.
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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).
- 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 µl 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.
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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).
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