Juvenile prey induce antipredator behaviour in adult predators

It is generally assumed that the choice of oviposition sites in arthropods is affected by the presence of food for the offspring on the one hand and by predation risk on the other hand. But where should females oviposit when the food itself poses a predation risk for their offspring? Here, we address this question by studying the oviposition behaviour of the predatory mite Amblyseius swirskii in reaction to the presence of its counterattacking prey, the western flower thrips Frankliniella occidentalis. We offered the mites a choice between two potential oviposition sites, one with and one without food. We used two types of food: thrips larvae, which are predators of eggs of predatory mite but are consumed by older predator stages, and pollen, a food source that poses no risk to the predators. With pollen as food, the predators preferred ovipositing on the site with food. This might facilitate the foraging for food by the immature offspring that will emerge from the eggs. With thrips as food, female predators preferred ovipositing on the site without thrips. Predators that oviposited more on the site with thrips larvae killed more thrips larvae than females that oviposited on the site without food, but this did not result in higher oviposition. This suggests that the females killed thrips to protect their offspring. Our results show that predators display complex anti-predator behaviour in response to the presence of counter-attacking prey.