DISTRIBUTION OF CHILLI THRIPS, SCIRTOTHRIPS DORSALIS (THYSANOPTERA: THRIPIDAE), IN PEPPER FIELDS AND PEPPER PLANTS ON ST. VINCENT

Abstract

Scirtothrips dorsalis Hood is a significant pest of various vegetable, ornamental, and fruit crops. Its biology and management are little known in the agro-ecosystems in western hemisphere. We investigated distribution patterns of S. dorsalis in fields and plants of ‘Scotch Bonnet’ pepper, Capsicum chinense Jacq., on St. Vincent in 2004 and 2005. Scirtothrips dorsalis adults and larvae were abundant on top leaves of the pepper plants followed by middle leaves, lower leaves, flowers and fruits. The spatial distribution of S. dorsalis adults and larvae on pepper was analyzed by using Taylor’s power law and Iwao’s patchiness regression. These results were compared with the Index of Dispersion, Mean Crowding, Green’s Index and Lloyd’s Patchiness Index. In Oct 2004, the distributions of S. dorsalis adults on the top leaves were aggregated in 24- and 48 m2-plots. In the smaller plots adults were distributed in a regular pattern. The distribution of larvae on the top leaves was aggregated irrespective of plot size. In Williams Farms on Mar 2005, the distribution of adults was aggregated in the largest plots (48 m2). In all other plots, the distribution of adults was regular as described by Taylor’s power law and Iwao’s patchiness regression. In Baptist Farms on March 2005, the distribution of adults according to both models was aggregated irrespective of plot size. The optimum number of samples from a 24 m2 plot was 9 with a precision of 40% when there were 0.5 individuals per top leaf of ‘Scotch Bonnet’ pepper. However if the estimated density was 2 individuals per top leaf, 9 samples from a same sized area were sufficient at the 10% precision level. This information is essential to the development of a scouting-based integrated management program for S. dorsalis. Based on this information, incipient infestations of S. dorsalis easily can be detected by examining young top leaves.