The enemy of my enemy is not always my friend

Maximilien A.C. Cuny, Mitchel E. Bourne, Marcel Dicke and Erik H. Poelman

"Male Crab Spider Thomisus onustus with Bee" by gailhampshire
“Male Crab Spider Thomisus onustus with Bee” by gailhampshire

Carnivorous arthropods (such as insects and spiders), which feed on herbivores, are usually said to be beneficial for plants. They lower feeding damage on the plant, allowing plants to grow more and produce more seeds. Because of these beneficial effects, some plants have structures that provide housing or a food source to carnivorous arthropods, and when plants are under attack by herbivores they produce volatile compounds which are known to attract the carnivorous enemies of herbivores. However, there are some cases in which the presence of carnivores has negative effects on plants. In this study, we present such cases and theorize about their consequences.

Some carnivores also feed on plant tissues (in this case they are called omnivores). They can cause an increase in plant damage when there are not many of their prey present. Other negative effects are less obvious and are only revealed when you take other interactions in the arthropod community into account. For example, carnivores may disrupt beneficial interactions among plants and other arthropods, such as pollinators or smaller carnivores. Pollinators, like bees or bumblebees, can be consumed or scared away when carnivores are present on the flowers, which leads to a lower seed production. Also, some carnivores are deterred or consumed by a top-carnivore, which benefits plant-feeding insects.

Finally, carnivorous arthropods may interfere with plant volatile communication. Composition of volatile blends can change in the presence of carnivores, deterring their counterparts from the plant or even attracting more herbivores towards the plant! In order to have a better understanding of natural interactions among plants and arthropods, we encourage future studies to take negative effects of carnivorous arthropods on plants more into account. The best way to do this is by performing experiments with plants in their natural environment.

Read the Review in full here

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