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How larvae of Thrips tabaci reduce the attack success of phytoseiid predators Bakker, F.M.; Sabelis, M.W. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. AbstractNeoseiulus barkeri (= Amblyseius mckenzieO and Amblyseius cucumeris (Acari:Phytoseiidae) are used as control agents of Thrips tabaci (Insecta:Thripidae) in greenhouse crops. Their success in capturing prey larval stages is related to both the feeding state of the predators and to the size of the larvae. When starved, predators are more successful in seizing larvae. Upon contact with a starved predator second stage prey larvae incur a lower death risk than first stage larvae. The larvae of T. tabaci reduce the attack success of their predators by jerking the abdomen and by producing a drop of rectal fluid. When this defensive behaviour is prevented by anaesthetising the larvae with CO2, predator attack success increases. Anaesthesia does not, however, level out the difference in death risk of the two larval stages. Conceivable causes for this discrepancy are discussed. Availability of suitable prey is dependent on the dynamics of the age structure of the prey population and, hence, may be lower than total thrips density suggests. If so, alternative food sources may be important to maintain the predator population.

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Abstract.A modified method for clearing, staining and mounting plant-inhabiting mites is proposed. With this method, all mites can be cleared with a single agent and mounted in a single medium. The stain added to the mounting medium enhances the clarity of the fine structures of soft-bodied mites under phase contrast and more significantly under bright field microscopy.

Both laboratory tests with the open glass plate method of Louis & Ufer (1995) and a field study in a vineyard were carried out to test the side effects of the two fungicides, Dithane Ultra WG75 and Polyram Combi WG70, on the predatory mite Typhlodromus pyri Scheuten (Acarina: Phytoseiidae). The effects of both fungicides in the residual contact test in the laboratory were more pronounced than the actual effects obtained in the field even after multiple application of the test products. The study results suggest, that for the selected test products the current laboratory guidelines correctly triggered the field test. Methodological problems of the laboratory test due to the repellent effect of the fungicides are discussed.

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