A review of trophic interactions and their implications for biological control of arthropod pests in agroecosystems

Abstract

In the last four decades there has been considerable interest in understanding the role of food web dynamics in the maintenance of plant productivity in ecosystems. This topic is particularly important in agroecosystems where the attack of erbivores can reduce plant productivity and cause severe economic damage to crops. The hypothesis that natural enemies indirectly regulate plant productivity through the suppression of herbivore populations (top-down control or trophic cascade hypothesis) has been the classical framework for biological control practitioners and ecologists interested in this topic. This hypothesis has proven to be controversial because empirical evidence shows that interspecific interactions among natural enemies in the third trophic level disrupt the top-down effects responsible for the suppression of herbivores and for the indirect benefits to plant productivity. Intraguild predation (IGP) is an important ecological process that can potentially dampen top-down control and contribute to reduce plant productivity due to the attack of unsuppressed herbivores. Thus, when aiming at the development of biological control programs with multiple species of natural enemies in the third or upper trophic levels, researchers must screen for some desirable traits of competing natural enemies. When both predators and parasitoids are present, predators are desirable in the system only if they do not eat parasitized hosts, which would disrupt parasitoid populations. When only predators are present, biological traits like mobility, body size, foraging strategy, level of diet specialization and species assemblage composition should be carefully investigated. These biological traits are related to the prevalence and intensity of IGP, to the choice and number of species to use in the program and to the choice of developmental stages to be introduced into crop fields. Observating these parameters and decision criteria may be crucial for the success of biological control programs.