Osservazioni sulla densità di popolazione diLymantria disparl. nelle principali aree subericole della Sardegna

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.