SCREEN HOLE SIZE AND BARRIERS FOR EXCLUSION OF INSECT PESTS OF GLASSHOUSE CROPS

Laboratory trials were conducted to determine the effectiveness of screens as barriers to five major greenhouse pests. Four screen types with a range of hole sizes were tested: high density polyethylene sheets perforated with holes that were in the center of an indentation on one side and a corolla of material on the opposite side; a woven mesh of polyethylene strands; a filter of unwoven polyester; and woven brass strainer cloth. Liriomyza trifolii (Burgess), Aphis gossypii Glover, Myzus persicae (Sulzer), Bemisia tabaci (Gennadius), or Frankiniella occidentalis (Pergande) were placed in a cage with a test screen separating them from a source of light and food. The insects' ability to pass through any barrier could not be predicted solely from thoracic width and hole size. Hole geometry or the way in which holes were formed were important elements in insects' exclusion. The most effective barriers to insect penetration correspondingly reduced air flow. The unwoven polyester filter designed specifically as an insect barrier did not restrain any of the insects under the methodology used. Results suggest that the maximum hole sizes for exclusion were: L. trifolii (640-mu-m), A. gossypii (341-mu-m), B. tabacci (462-mu-m) and F. occidentalis (192-mu-m).