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We investigated alfalfa and stinging nettle from the point of view of their potential to supply natural enemies of pests for protecting greenhouse cultures. We carried out a three year long study based on sweepnetting. The most frequent predatory insect was Orius niger (Wolff) in alfalfa and nettle. This species among others has an important potential in the biological control of thrips. Among ladybugs, the most important species in alfalfa and nettle were Propylea quatuordecimpunctata (Linnaeus), Coccinella septempunctata Linnaeus and Hippodamia variegata (Goeze), which consume significant amounts of aphids. The most frequent spider family in alfalfa and nettle was Thomisidae and Philodromidae. The dynamics of their prey composition suggests that these taxa present a significant suppressive force on pests. The predator thrips Aeolothrips intermedius Bagnall that feeds on phytophagous thrips, mites and other soft-bodied arthropods was also significant in the arthropod assemblage of alfalfa. Our three-year investigation showed that the abundance and the species richness of the natural enemies of greenhouse crops are suitably high in both alfalfa and nettle stands. The number of generalist predators, natural enemies of pests, the most versatile tools of pest management reached its peak between mid-May to late June in nettle whereas due to mowing, the highest values for alfalfa were recorded from June to mid-August.

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Recent years of studies have suggested that the common crab spider (Xysticus kochi) has a great potential against the western flower thrips (Frankliniella occidentalis) . The efficiency of applying a single predator against a pest however, is made uncertain by many different factors. Using a mixture of predators on the other hand, can overcome the difficulties of using a single-species agent, since different predators have different environmental demands and preying habits. Our experiments involved releasing a non-selected assemblage of arthropods, collected by sweep-net in alfalfa and stinging nettle, into greenhouse pepper stands. Interestingly, while there were twice as much thrips in the experimental greenhouses than in the control (mainly conventional) ones, crop yields were similar. The ratio of predators-preys in experimental greenhouses was not different from that in the control greenhouses, too. Probably the release of predators and lack of chemical treatments in experimental stands resulted in a 43% increase in the amount of Orius species. In search of a cost-effective, environment-friendly pest management method, the application of a mass-collected, non-selected assemblages of arthropods has a definite potential. Further investigations are needed to increase the efficiency and to monitor the potential drawbacks of this method.

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Puustinen, S., Koskela, T. and Mutikainen, P. (2004): Direct and ecological costs of resistance and tolerance in the stinging nettle. — Oecologia 139 : 76–82. Mutikainen P. Direct and

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