René R. Vargas M.1
The negative binomial and Neyman type A distributions accurately described P. ulmi aggregation within the tree. The mites formed aggregations on the leaves and showed a random distribution within the apple tree canopy. The minimum number of samples was determined so as to estimate the density of mites with different degrees of aggregation and coefficients of variation levels. A relatively stable number of samples was obtained above four mites per leaf. Through analysis of variance, it was possible to substantiate that a great variability occurred in the population's means of P. ulmi in the trees, suggesting the necessity ot studies to determine the mite distribution among the trees in the orchard.
1 Subestación Experimental Control Biológico La Cruz (INIA), Casilla 3, La Cruz, Chile.