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BACKGROUND The tomato russet mite (TRM), Aculops lycopersici, and powdery mildew (PM), Oidium neolycopersici, are two major problems in tomato cultivation for which no effective biocontrol solutions exist to date. In a greenhouse compartment, we investigated the potential of preventatively establishing the iolinid omnivorous mite Pronematus ubiquitus on potted tomato plants to control both pest and pathogen simultaneously. RESULTS Using Typha pollen, P. ubiquitus established well on tomato plants, with numbers reaching up to 250 motiles per tomato leaflet. The built‐up population was capable of controlling subsequent infestations with both TRM and PM. This represents the first report of an arthropod protecting a crop against pests as well as disease. CONCLUSION The implementation of P. ubiquitus in tomato crops could be a real game‐changer as it eliminates the need for repeated pesticide use or sulphur applications. The finding that arthropods can effectively control diseases opens up new opportunities for biological crop protection. © 2021 Society of Chemical Industry.

Supplying predators with alternative food can have short-term positive effects on prey densities through predator satiation (functional response) and long-term negative effects through increases of predator populations (numerical response). In biological control, alternative food sources for predators are normally supplied on the crop plants; using the litter-inhabiting food web as a source of alternative food for plant-inhabiting predators has received less attention. We investigated the effect of supplying plant-inhabiting predatory mites with alternative prey (astigmatic mites) in the litter on pest control. Predator (Amblyseius swirskii) movement and population dynamics of the pest (western flower thrips) and predators were studied on rose plants in greenhouses. Predators commuted between the aboveground plant parts where they controlled thrips, and the litter, where they fed on alternative prey, although the latter were a superior diet. Predators controlled thrips better in the presence of the astigmatic mites than in their absence. We show that predatory mites can form a link between aboveground pests and the litter food web, and propose that adding alternative prey to the litter of ornamental greenhouses can result in higher predator densities and increased biological control.

Repeated mass introductions of natural enemies have been widely used as a biological control strategy in greenhouse systems when the resident population of natural enemies is insufficient to suppress the pests. As an alternative strategy, supporting the establishment and population development of beneficials can be more effective and economical. The preventative establishment of predators and parasitoids, before the arrival of pests, has become a key element to the success of biological control programs. This “Predators and parasitoids-in-first” strategy is used both in Inoculative Biological Control (IBC), and in Conservation Biological Control (CBC). Here, we provide an overview of tools used to boost resident populations of biocontrol agents.

Our search for a suitable biological agent to control the tomato russet mite (TRM), Aculops lycopersici, was initiated in 2013. Neoseiulus californicus, Amblyseius andersoni, and Neoseiulus fallacis showed a promising pest reduction potential in a curative control strategy. Although these beneficials had a low survival on tomato and were not able to eradicate the pest, plants did not present typical TRM damage. However, their inability to establish in the tomato crop means that their commercial use would require repeated introductions, making their use too expensive for growers. Other predatory mites in the survey, such as the iolinids Homeopronematus anconai and Pronematus ubiquitus, showed the potential for a preventative strategy as they can establish and reach high densities on tomato with weekly or biweekly provision of Typha angustifolia pollen as a food source. When the tomato crop was adequately colonized by either iolinid, the development of TRM and any damage symptoms could be successfully prevented. The potential of iolinid predatory mites for biological control of eriophyids is discussed.

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Pronematus ubiquitus (McGregor) is a small iolinid mite that is capable of establishing on tomato plants. Once established, this mite has been shown to control both tomato russet mite, Aculops lycopersici (Tryon) (Acari: Eriophyidae), and tomato powdery mildew (Oidium neolycopersici L. Kiss). In the present study, we explored the effects of a number of alternative food sources on the oviposition rate in the laboratory. First, we assessed the reproduction on food sources that P. ubiquitus can encounter on a tomato crop: tomato pollen and powdery mildew, along with tomato leaf and Typha angustifolia L. In a second laboratory experiment, we evaluated the oviposition rate on two prey mites: the astigmatid Carpoglyphus lactis L. (Acari: Carpoglyphidae) and the tarsonemid Tarsonemus fusarii Cooreman (Acari: Tarsonemidae). Powdery mildew and C. lactis did not support reproduction, whereas tomato pollen and T. fusarii did promote egg laying. However, T. angustifolia pollen resulted in a higher oviposition in both experiments. In a greenhouse trial on individual caged tomato plants, we evaluated the impact of pollen supplementation frequency on the establishment of P. ubiquitus. Here, a pollen addition frequency of every other week was required to allow populations of P. ubiquitus to establish.

Integrated Pest Management (IPM) is successfully used on a year-round scale on only 15% of the area of roses under glass. Obstacles for further expansion of IPM practices among rose growers are the control of the spidermite Tetranychus urticae and the greenhouse whitefly Trialeurodes vaporariorum. The research stations of Naaldwijk, Aalsmeer and Boskoop have started initiatives in order to enlarge the choice of predator species available for Dutch growers. A series of greenhouse experiments were conducted to select phytoseiid mites suitable for commercial cut roses. Among ten species tested in experimental greenhouses, Euseius ovalis was found to be the most promising control agent of T. vaporariorum. Its efficacy against other pests and its compatibility with chemicals are the subject of further studies. Since E. ovalis is an exotic species formerly not commercially available, efforts are being made to obtain authorization for experimenting with this species in commercial greenhouses in the framework of new fauna protection regulations in The Netherlands.