Davide CONCONI, Luca NESSI, Dr. Prof. Martine ROWELL-RAHIER
Université de Neuchatel , Institut de Zoologie, Laboratoire d' Ecologie Animale
et Entomologie, Rue Emile-Argand 11, CH-2007 Neuchatel.
.
Tél: +4138 23 21 11, Fax: +4138 23 30 01
Dispersal of insects from their host plants is an important factor in the evolution of host use since dispersal provides insects with the ability of encountering new potential hosts, to select suitable host-plants, to escape competition, natural enemies or other plant-related unfavourable conditions and finally it tends to increase genetic variation within and sometimes among insect populations. Adults are usually more mobile than larvae but larval dispersal has been shown to occur in various phytophagous insects.
In our research we were interested in Oreina cacaliae (Coleoptera, Chrysomelidae) larval dispersal. O. cacaliae is an alpine leaf beetle, specialised on asteracean plants (Adenostyles, Senecio, Petasites). Larvae as well adults sequester plant pyrrolizidine alkaloid N-oxides for their defence. We investigated the larval dispersal since it might be a mean to select highly suitable host-plants. The adults are flightless, aposemantic and disperse little.
The study area was on Adenostyles alliariae grassland in the Val Ferret (Walliser Alps, Switzerland). In a control and treatment with tanglefoot excluding the host-plant colonisation or dispersal, larvae were marked and resighted. The results show that larvae of second, third, fourth (last) instar are mobile and able to colonise new host plants. On the other hand females do not seem to discriminate host plant on the basis of their previous colonisation by larvae. Thus larval dispersal probably play an important role in determining the local distribution of the larvae.