La Dinamica di popolazione diLymantria disparL. in Sardegna: 1.: indicatori della gradazione ricavati dalle ovideposizioni

The present work, dealing with the egg stage ofLymantria disparL., forms part of a 9-year (1972-1980) research program on the population dynamics of the insect in a N. E. Sardinian cork-growing region. Egg-cluster counts (per hectare of forest surface) showed that total defoliation is to be expected every 7-9 years, that population density increase is not necessarily concomitant, and that different population densities may occur even in adjacent biotopes. The average egg count per cluster was low .(329 to 353) in peak population years and in the first year of retrogradation (288 to 339), but appreciably higher in years of latency and progradation (674 to 726). Egg sterility showed lower (from 1.7% to 6.0%) in latency years than in years of progradation, peak and retrogradation (from 7.6% to 18.4 %). The height above ground of ovideposition on the cork-oak trunks also varied. In latency years, more than 75% of the c1usters were laid below 2 metres: in progradation years, from 40% to 60% at above 2 m. In peak years, more than 75% were laid above 6 m, and in retrogradation years 40% to 60% between 2 m and 6 m. Information gathered on parasites (Ooencyrtus kuwanai(How.) andAnastatus disparisRuschka) and predators (Dermestes lardariusL. andHaplocnemus jejunusKinsenw.), which, at most, reached 27.9% in 1978 - a latency year forL. dispar-, would suggest that these are not of prime significance in controlling the defoliating populations. Statistic correlations are shown between egg-cluster dimensions and egg count per cluster, in particular the linear regression between the length of the egg-cluster major axis and total eggs in the cluster (y = – 11.86 + 11.26 x), in order to enable estimates of population levels to be made more rapidly. If correctly used on a large scale, the indicators analysed taken as a whole should enable sufficiently reliable forecasts to be made ofL. disparpopulation levels and gradation phases, forming the basis of commen· surate programming for the protection ofQuercus suberforests from defoliation.