Biological Control of Western Flower Thrips with Orius laevigatus (Heteroptera: Anthocoridae) in Organic Strawberries in Portugal
In Portugal, strawberries are a key crop for the organic farming market. In 1990 and 1991 western flower thrips (WFT) were a major pest of strawberries in the Algarve. In 1992 and 1993 WFT populations were considerably lower and not economically important. In 1993 there was a maximum of 4.3 thrips per strawberry flower. The predator Orius laevigatus (Fieber), which is a common, naturally occurring species in Portugal, was experimentally released in strawberry plantings. Although numbers of thrips per flower were lower in cages where they were released, these numbers were not significantly different from numbers of thrips in cages without the predator. In one cage where O. laevigatus was released, there was an appreciable growth of the weed Chamaemelum mixtum (L.). The latter produced large amounts of pollen and it is not clear if the lower thrips populations in this case, which happened after the weed flowering, were caused by an increase of O. laevigatus, as a result of feeding on the pollen, or by a thrips transfer to the Compositae weeds attracted by the pollen.