Indirect Mutual Interference in Parasitoids

Abstract

Mutual interference, i. e. any kind of interaction between predators or parasitoids reducing searching efficiency, is potentially able to stabilize the dynamics of predator-prey or parasite-host systems. It is often considered to be the result of behavioural interaction between adults in which search time is wasted. Due to this loss of time, such direct mutual interference has an immediate effect on the searching efficiency in the patch. Here, we show that the solitary parasitoid Leptopilina heterotoma, in contrast to earlier findings, does not exhibit mutual interference. Yet, because of the occurrence of superparasitism and the consequent increase in patch time, searching efficiency at the population level clearly decreases. This we call indirect mutual interference, because it is not reflected in a decrease in the searching efficiency at the patch level. Using a simple population model we show that it is different from pseudo-interference. Other forms of indirect mutual interference are sex ratio shifts and decreasing fecundity. If such phenomena are to be included into the concept of interference, other criteria than the classical searching efficiency should be developed in order to assess the significance of these phenomena on the dynamics of populations.