It is well established that plants provide alternative foods to predators of herbivorous arthropods. This provision may facilitate protection against herbivory. However, plants often cannot prevent other organisms from utilizing these foods as well. There are many examples of herbivorous arthropods that can feed on plant‐provided foods such as extrafloral nectar and pollen. The question therefore arises whether individual plants still gain protection when not only the predators, but also the herbivores, can feed on these foods. We investigated this question using a mathematical model and experiments that assessed the impact of supplementary pollen on the dynamics of predatory mites (Iphiseius degenerans (Berlese)) and herbivorous thrips (Frankliniella occidentalis (Pergande)), two arthropods capable of using pollen for reproduction. Replicated greenhouse experiments showed that addition of pollen every two weeks to one young mature leaf of a male‐sterile cucumber plant increased predator population growth and greatly reduced herbivore numbers. A stage‐structured predator–prey–pollen model with experimentally established parameters gave reasonably accurate predictions of population trends observed in the greenhouse experiments with and without pollen. Model analysis yielded three important results. First, herbivore (prey) equilibria always settled to lower values in the presence of pollen. Second, mean herbivore numbers during the transient phase following predator release were not always lower under pollen supply, depending on the initial numbers of predators and prey. Third, limiting the plant area covered with pollen led to a decrease in mean herbivore numbers, provided that the predators aggregated in (and thereby “monopolized”) pollen patches. The latter result may explain why plants provide alternative foods at specific sites.

The predatory mite Amblyseius swirskii quickly became one of the most successful biocontrol agents in protected cultivation after its introduction into the market in 2005 and is now released in more than 50 countries. There are several key factors contributing to this success: (1) it can control several major pests including the western flower thrips, Frankliniella occidentalis, the whiteflies Bemisia tabaci and Trialeurodes vaporariorum and the broad mite, Polyphagotarsonemus latus, simultaneously in vegetables and ornamental crops; (2) it can develop and reproduce feeding on non-prey food sources such as pollen, which allows populations of the predator to build up on plants before the pests are present and to persist in the crop during periods when prey is scarce or absent; and (3) it can be easily reared on factitious prey, which allows economic mass production. However, despite the fact that A. swirskii provides growers with a robust control method, external demands were initially a key factor in promoting the use of this predator, particularly in Spain. In 2006, when exports of fresh vegetables from Spain were stopped due to the presence of pesticide residues, growers were forced to look for alternatives to chemical control. This resulted in the massive adoption of biological control-based integrated pest management programmes based on the use of A. swirskii in sweet pepper. Biological control increased from 5 % in 2005, 1 year before A. swirskii was commercially released, to almost 100 % of a total 6,000 ha of protected sweet pepper in Spain within 3 years. Later, it was demonstrated that A. swirskii was equally effective in other crops and countries, resulting in extensive worldwide use of A. swirskii in greenhouses.

Tomato plants have their leaves, petioles and stems covered with glandular trichomes that protect the plant against two-spotted spider mites and many other herbivorous arthropods, but also hinder searching by phytoseiid mites and other natural enemies of these herbivores. This trichome cover creates competitor-free and enemy-free space for the tomato russet mite (TRM) Aculops lycopersici (Acari: Eriophyidae), being so minute that it can seek refuge and feed inbetween the glandular trichomes on tomato cultivars currently used in practice. Indeed, several species of predatory mites tested for biological control of TRM have been reported to feed and reproduce when offered TRM as prey in laboratory experiments, yet in practice these predator species appeared to be unable to prevent TRM outbreaks. Using the phytoseiid mite, Amblydromalus limonicus, we found exactly the same, but also obtained evidence for successful establishment of a population of this predatory mite on whole plants that had been previously infested with TRM. This successful establishment may be explained by our observation that the defensive barrier of glandular plant trichomes is literally dropped some time after TRM infestation of the tomato plants: the glandular trichome heads first rapidly develop a brownish discoloration after which they dry out and fall over onto the plant surface. Wherever TRM triggered this response, predatory mites were able to successfully establish a population. Nevertheless, biological control was still unsuccessful because trichome deterioration in TRM-infested areas takes a couple of days to take effect and because it is not a systemic response in the plant, thereby enabling TRM to seek temporary refuge from predation in pest-free trichome-dense areas which continue to be formed while the plant grows. We formulate a hypothesis unifying these observations into one framework with an explicit set of assumptions and predictions to be tested in future experiments.Electronic supplementary materialThe online version of this article (doi:10.1007/s10493-012-9638-6) contains supplementary material, which is available to authorized users.

Preselection of predatory mites to improve year-round biological control of Western flower thrips in greenhouse crops van Houten, Y.M.; van Rijn, P.C.J.; Tanigoshi, L.K.; van Stratum, P.; Bruin, J. Published in: Entomologia Experimentalis et Applicata Link to publicationCitation for published version (APA): van Houten, Y. M., van Rijn, P. C. J., Tanigoshi, L. K., van Stratum, P., & Bruin, J. (1995). Preselection of predatory mites to improve year-round biological control of Western flower thrips in greenhouse crops. Entomologia Experimentalis et Applicata, 74, 225-234. 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. Download date: 04 Apr 2019Entomologia Experimentalis etApplicata 74: 225-234, 1995. Key words: biological control, Thripidae, Frankliniella occidentalis, Phytoseiidae, Amblyseius, diapause, drought tolerance, predation, oviposition AbstractIn spring and summer, two groups of natural enemies are successfully used for biological control of western flower thrips, Frankliniella occidentalis (Pergande) in greenhouses: phytoseiid mites (Amblyseius cucumeris (Oudemans) and, to a lesser extent, A. barkeri (Hughes)) and anthocorid bugs (Orius spp.). During winter, however, these predators often fail to control the pest. One likely cause for failure is the predators' tendency to enter diapause under short day conditions. In addition, eggs of predatory mites are generally susceptible to low humidity conditions, which often arise in greenhouses when outside temperatures drop below zero, or at bright, hot days in summer. In search for a thrips predator that is not hampered by these conditions, five subtropical phytoseiid species were selected which were known to feed on thrips: A. hibisci (Chant), A. degenerans Berlese, A. limonicus s.s. Garman and McGregor, A. scutalis (Athias-Henriot) and A. tularensis (Congdon). These species were compared to A. cucumeris and A. barkeri, with respect to the following features: (1) predation and oviposition rate with young E occidentalis larvae as prey, (2) oviposition rate on a diet of sweet pepper pollen, (3) drought tolerance spectrum of eggs, and (4) incidence of reproductive diapause under short day conditions. The results showed that A. limonicus exhibited the highest predation and oviposition rates on a diet of thrips...