Multitrophic interactions among plants, aphids, alternate prey and shared natural enemies - a review

Abstract

Abstract. Given the generalist tendencies of most predatory arthropods, it is widely thought that their impact on a particular prey species in a given habitat (e.g., an insect pest in a crop) will depend frequently on the local availability of other prey (which for omnivorous predators, can include plant resources, such as fruit and pollen). Thus, from a slightly different perspective, aphids, other herbivorous insects, and plants often may interact indirectly by sharing natural enemies. Such interactions may be either negative or positive, as in the concepts of apparent competition and apparent mutualism, and may therefore have variable impact on the herbivores' host plants as well. I examine the different mechanisms for such indirect effects among herbivores as explored in the experimental literature. An impressive collective effort by numerous researchers recently has expanded considerably our empirical base of support for a variety of hypothesized mechanisms; aphids stand out as the most commonly studied subjects in research on these mechanisms. I therefore focus especially on the recent literature of cases involving aphids interacting indirectly with other prey for generalist predators. My remarks are organized by considering how the availability of alternate prey may alter functional and numerical (aggregative and reproductive) responses of predators to focal prey density. Although the distinctions among these different classes of predator responses and the associated indirect effects are often blurred and scale-dependent, this classification remains useful for organizing the diverse ways in which aphids have been found to participate in indirect interactions among prey as mediated by predators. Collectively, the results of the numerous studies reviewed here suggest that many such indirect interactions likely occur frequently in natural settings, with consequences ultimately for host plant performance.

Food Relationships

“…Most probably the predator was better able to attach to plants with reduced -wax bloom, and its search rate was elevated. Handling time of prey, Additional examples are provided by Lucas et al (2004) and Koch et al (2005) , as discussed further by Evans (2008) . Prey activity may infl uence the relative amounts of co -occurring prey consumed.…”

Stage specific consumption and utilization of aphids, conspecific and heterospecific eggs by two species of Coccinella (Coleoptera: Coccinellidae)

“…It is assumed that because they are best at exploiting aphids (Pettersson et al, 2005;Evans, 2008) aphidophagous ladybirds will grow better when feeding on aphids than on non-aphid prey. However, due to their short life span and patchy distribution, the availability of aphids is quite uncertain, which may sometimes result in ladybirds starving in the field.…”

The spatial distribution of canopy-resident and ground-resident cereal aphids (Sitobion avenae and Metopolophium dirhodum) in winter wheat

“…The reason for these differences are unknown, but they probably relate to the initial conditions of the establishing aphid population (i.e. localised immigration of winged immigrants and the resident overwintering population), microclimatic and topographical differences, differences in soil fertility influencing crop growth and differences in the impact of natural enemies (Irwin et al 2007;Evans 2008).…”