The impact of floral resources and omnivory on a four trophic level food web

Abstract

Omnivory is common among arthropods, but little is known about how availability of plant resources and prey affects interactions between species operating at the third and fourth trophic level. We used laboratory and field cage experiments to investigate how the provision of flowers affects an omnivorous lacewing, Micromus tasmaniae (Hemerobiidae) and its parasitoid Anacharis zealandica (Figitidae). The adult lacewing is a true omnivore that feeds on both floral resources and aphids, whereas the parasitoid is a life-history omnivore, feeding on lacewing larvae in the larval stage and floral nectar as an adult. We showed that the effect of floral resources (buckwheat) on lacewing oviposition depends on prey (aphid) density, having a positive effect only at low prey density and that buckwheat substantially increases the longevity of the adult parasitoid. In field cages, we tested how provision of flowering buckwheat affects the dynamics of a four trophic level system, comprising parasitoids, lacewings, pea aphids and alfalfa. We found that provision of buckwheat decreased the density of lacewings in the first phase of the experiment when the density of aphids was high. This effect was probably caused by increased rate of parasitism by the parasitoid, which benefits from the presence of buckwheat. Towards the end of the experiment when the aphid populations had declined to low levels, the effect of buckwheat on lacewing density became positive, probably because lacewings were starving in the nobuckwheat treatment. Although presence of buckwheat flowers did not affect aphid populations in the field cages, these findings highlight the need to consider multitrophic interactions when proposing provision of floral resources as a technique for sustainable pest management.

Habitat manipulation to mitigate the impacts of invasive arthropod pests

“…In a similar way, presence of alternative prey for generalist predators may in some cases decrease predation rates on the target pest (Prasad and Snyder 2006) tasmaniae is a true omnivore that feeds on floral nectar and aphids in its adult life stage whereas A. zealandica is a life-history omnivore that feeds only on sugar-rich resources such as nectar as an adult and parasitizes lacewings as larvae. Laboratory trials showed that fecundity and longevity of M. tasmaniae is positively affected by floral availability mainly when aphid availability is low (Robinson et al 2008;Jonsson et al 2009). In a field cage experiment, provision of flowering buckwheat decreased lacewing densities when aphid availability was high, probably because buckwheat primarily benefits the lacewing parasitoid during such conditions (Jonsson et al 2009).…”

“…Laboratory trials showed that fecundity and longevity of M. tasmaniae is positively affected by floral availability mainly when aphid availability is low (Robinson et al 2008;Jonsson et al 2009). In a field cage experiment, provision of flowering buckwheat decreased lacewing densities when aphid availability was high, probably because buckwheat primarily benefits the lacewing parasitoid during such conditions (Jonsson et al 2009). One way to decrease the risk for this type of unwanted side effects is to search for food plants that selectively benefit natural enemies of the pest but not the pest itself or key antagonists (Baggen et al 1999;Begum et al 2006;Lavandero et al 2006;Araj et al 2008).…”

Genotypically diverse cultivar mixtures for insect pest management and increased crop yields

“…; Jonsson et al . ). Some natural enemies provide better control on plants that are morphologically less complex (Carter, Sutherland & Dixon ; Legrand & Barbosa ).…”

Alternative food promotes broad mite control on chilli pepper plants

“…Here, we demonstrate that this increment in the number of predatory mites in the absence of the prey can be a strategy to protect plants from pest infestations, similar to what was found by Ramakers (1990) for thrips. Instead of supplying alternative food on the plants, intercropping with other plant species that provide alternative food can also be used to enable early establishment of predators (Landis et al 2000;Norris and Kogan 2005;Amaral et al 2013;González-Fernández et al 2009;Jonsson et al 2009;Rezende et al 2014). This remains to be investigated for pepper cropping systems.…”