How Plants Benefit From Providing Food to Predators Even When It Is Also Edible to Herbivores

Abstract

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.

Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

“…Similar effects might also be achieved by adding a non-pest alternative food source, such as pollen. Several studies have shown the benefit of pollen in terms of enhancing pest control (Nomikou et al 2002(Nomikou et al , 2009van Rijn et al 2002), but so far, this has not resulted in large-scale applications. Our results furthermore suggest that it might be advantageous to allow or create some pest species diversity in a crop, rather than to try to exterminate all phytophages present.…”

Alternative food and biological control by generalist predatory mites: the case of Amblyseius swirskii

“…Apple pollen was the most suitable alternative food, and supplementing A. swirskii with it resulted in better control of western flower thrips on chrysanthemum (Delisle et al 2015b). Similarly, Leman and Messelink (2015) test various types of alternative food for A. swirskii and Amblydromalus limonicus, but they specifically consider the possibility that western flower thrips also benefits from this food (van Rijn et al 2002). In short-term laboratory experiments, they show that predation of thrips by individual A. swirskii was reduced when pollen was present.…”

“…A relevant question therefore is how to avoid that predators preferentially feed on the supplied food, resulting in temporary increases of pest populations. In our opinion, supplementing predators such as A. swirskii with superior alternative food is a viable biological control practice, as several studies have shown (van Rijn et al 2002;Nomikou et al 2010;Delisle et al 2015b;Leman and Messelink 2015). Especially when predators and alternative food are introduced into the crop before pests occur, the densities of the predators will, after some Exp Appl Acarol (2015) 65:413-418 415 time, be limited by the availability of the alternative food.…”

“…Synchronization of natural enemies with the pest implies that natural enemy densities will decrease when pest densities are low, and this may facilitate new pest invasions. In contrast, pest outbreaks can be prevented by maintaining populations of generalist natural enemies through the presence of alternative food sources (Collyer 1964;Ramakers 1990;Karban et al 1994;Hanna et al 1997;Walde et al 1997;van Rijn et al 1999;Nomikou et al 2002;van Rijn et al 2002;Liu et al 2006;Nomikou et al 2010). The presence of such a standing army of natural enemies also remedies the third objection to using generalists, i.e.…”

“…Until recently, studies on alternative food for phytoseiid natural enemies mainly considered non-pest foods, such as pollen, nectar or relatively harmless herbivorous arthropods (Bakker and Klein 1992;Hanna et al 1997;Karban et al 1997;van Rijn et al 2002). This changed with the introduction of the predatory mite Amblyseius swirskii.…”