OSSERVAZIONI SULLA DISTRIBUZIONE SPAZIALE DI OVIDEPOSIZIONI E NIDI DI MALACOSOMA NEUSTRIUM (L.) IN SUGHERETE DELLA SARDEGNA (1)

In order to determine sampling methods for the Malacosoma neustrium population, in 1998-99, the insect fecundity was observed and its population density and the spatial distribution of its tents and egg masses recorded. The length of cylindrical egg mass (x) was the most highly correlated single measurement with actual number of eggs per mass (y) (logia y = 1.3263+1.09209 log10 x; R2= 0.78). An insect preference in laying the egg masses and making tents in the South facing side of the trees was observed. The spatial distribution of egg masses and tents among the trees was compared with Poisson's, Neyman's and negative binomia! mathematical models. The aggregated models proved to be more suitable to represent the actual spatial distribution. Taylor's power law parameters and lwao's regression were needed to determine the number of plants to be sampled for estimating the population means at two fixed levels of precision (D = 0.10; D = 0.25). In low egg masses density condition a high number of trees should be observed (D = 0.10; x = 1; n = 223) which could be reduced to 36 plants at a lower precision level. The development of a sequential sampling plan, based on Taylor's parameters, has been outlined.