BIOLOGY OF THE WEEVIL TRICHOSIROCALUS TROGLODYTES AND IMPACT ON ITS HOST PLANTAGO-LANCEOLATA

We tried to measure the effects that a native parasite may cause to it s native host by studying some biological properties of the specialist weevil Trichosirocalus troglodytes in relation to the impact on its h ost Plantago lanceolata. Density and activity of the weevil were estim ated in four different ways: Tullgren, sweep net, capture-recapture an d counting feeding holes in the leaves. The sweep net gave reliable in formation on relative densities and on presence of the weevil on the s pikes, but the results were much influenced by the diurnal and seasona l activities of the weevil. Most eggs were laid during spring in the o ldest leaves and most larvae were found in the caudex of the plant. We evils of the new generation appeared from July onwards and developed f light muscles. The impact of 0, 3, 6 and 12 larvae on the spikes and t he rosette of different P. lanceolata genotypes was investigated. The number of seeds per spike decreased linearly with the number of larvae added to the spikes. No effect on plant performance was found when th e larvae were added to the rosette. The weevil spreads its risks by us ing different plant parts as oviposition sites during a prolonged peri od, hereby softening the ''pain'' put upon the plant.