Università degli studi di Sassari, Facoltà di Agraria - Gallizzi
Abstract
A two year survey (1980·81) was carried out in zones adjacent to roads running through the principal
Sardinian cork growing regions. Every 5 km in each region, egg clusters were counted on 40
trees, i.e. 4 radial lines of 10 trees (each line directed towards one of the cardinal points). The
results showed a wide population density variability spectrum, indicating those areas likely to
suffer total defoliation; summer observations confirmed correspondence between egg cluster counts
and damage. Whereas populations in the north of the island showed the highest levels, in the south
they were at latency levels. This staggered population fluctuation may possibily be explanied by
different sub-populations having been formed due to the distance and natural barriers between the
two regions. The survey not only showed the importance of the insect's active and passive diffusion
phenomena in determining defoliation extension, but also verified that food availability is a major
factor in controlling population density. The relative scarcity in high density populations limited fecundity
and prolificity and at times starvation caused mass mortality in the larvae
