Biological control of thrips (Thysanoptera) by Orius laevigatus (Heteroptera: Anthocoridae) in organically-grown strawberries

In Portugal, strawberries are a key crop for the organic farming market. In 1990 and 1991 Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), the western flower thrips (WFT), was a major pest of strawberries in the Algarve. In 1993, the predator Orius laevigatus (Fieber) (Heteroptera: Anthocoridae), a common naturally occurring species in Portugal, was experimentally released in strawberry plantings. Numbers of thrips per flower were lower in cages where the Orius were released. In one of the cages where O. laevigatus was released there was also an appreciable growth of the composit weed Chamaemelum mixtum (L.). The later produced large amounts of pollen and there was a lower thrips populations and a higher Orius population in this plot, which happened after the weed flowering. It is not clear if this thrips reduction was caused by the increase of O. laevigatus, as a result of feeding on the weed pollen, or by a similar transfer of thrips to the Compositae also attracted by their pollen. A knowledge of the role of composit weeds in the reduction of thrips populations on strawberries would be very useful.