Frequency distribution of Malacosoma neustria (L.) egg masses and nests in cork oak forests

In order to define a reliable sampling method for defoliating moth, data on population density of Malacosoma neustria (L.) were collected. Wild M. neustria populations were monitored at seven field localities in the major cork oak forests of Sardinia, in the spring of 1998 and 1999. Egg mass and nest location on trees was analysed. An insect preference in laying the egg masses on the East and South facing side of the tree canopy was recorded. Nest distribution on the trees followed the same trend. The spatial distribution among trees was analysed taking into account the fitting of Poisson's, Neyman's and negative binomial mathematical models to the actual distributions. In all localities nests had a gathered distribution among trees while the egg mass location showed a different pattern. Taylor's power law regression was used to determine sample size requirements necessary for estimating population average with two fixed levels of precision (D = 0.10; D = 0.25). At low egg ma·'S density condition a high number of trees should be observed (D = 0.10; x = 0.5+1 ; n = 370 -:- 223 ). Using Taylor's power law parameters at a precision level D = 0.25 with a population density of l egg mass per tree, it is necessary to examine 36 trees. The results obtained encourage us to suppose that the observation of a limited part of the tree offers reliable data to estimate the pest population density.