Bean Leaf Beetle 1 : Micro-Spatial Patterns and Sequential Sampling of Field Populations 2

Abstract

Dispersion of teneral and mature bean leaf beetles (BLB) populations approximated a negative binomial with the single individual being the basic component of the distribution. Aggregation indices indicated departure from randomness but only a slight degree of clumping. The common k of the negative binomial was distinctly lower for callow BLB than for mature BLB. The degree of aggregation of mature BLB was correlated with the seasonal fluctuations in abundance of the callow BLB. It is suggested that the ovipositing behavior of females is the causative factor of subsequent BLB aggregation. Using sampling decision rules for adult BLB based on Morisita's I∂ and Lloyd's coefficients, 30–50 random samples of 20 sweeps adequately estimate BLB densities in homogeneous soybean fields. Simple sequential sampling methods suited to ecological population studies and estimation of population levels in relation to a predetermined threshold are suggested.