Abstract
Natural enemy guilds normally forage for prey that is patchily distributed simultaneously. Previous studies have investigated the influence of conspecific interactions and prey distribution on the functional response of natural enemies. However, little is known about how prey distribution and heterospecific interactions between natural enemies could affect their foraging efficiency. We examined the effects of prey distribution (aggregate and uniform) and heterospecific interactions on the functional response of a predator, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and a parasitoid, Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) to the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). Type II functional responses were observed in all experiments. Functional response curves of single H. axyridis or A. gifuensis were higher in the aggregate treatment than in the uniform treatment when aphid densities were between 40–180 or 70–170, respectively. When comparing between aggregate and uniform treatments with the heterospecific enemy occurrence, no differences were found in the parasitism efficiency of A. gifuensis, while H. axyridis consumed more aphids in the aggregate treatment than in the uniform treatment when aphid densities were between 50–230. The functional response of individual H. axyridis was not affected by A. gifuensis under two aphid distributions. However, the functional response of a single A. gifuensis and the treatment when A. gifuensis concurrently with H. axyridis overlapped in uniform treatment of above approximately 150 aphids. Our results indicate that the predation rate of H. axyridis was affected by aphid distribution, but was not affected by heterospecific interactions. The parasitism rate of A. gifuensis was affected by aphid distribution, and by heterospecific interactions in both the aggregate and uniform treatments. Thus, to optimize the management efficiency of M. persicae, the combined use of H. axyridis and A. gifuensis should be considered when M. persicae is nearly uniformly distributed under relatively high density.
Highlights
Biological control by natural enemies is an environment-friendly and effective approach in regulating pest population, and it has received increasing research interest and has long been applied as part of integrated pest management (IPM) strategies [1,2,3]
For single H. axyridis treatment, we found that aphid density, aphid distribution, and the interaction between aphid density and aphid distribution had a significant effect on aphid consumption by H. axyridis adults (Table 2)
Density dependent predation rate of H. axyridis was affected by aphid distribution, but not influenced by heterospecific interactions
Summary
Biological control by natural enemies is an environment-friendly and effective approach in regulating pest population, and it has received increasing research interest and has long been applied as part of integrated pest management (IPM) strategies [1,2,3]. Multiple enemies are involved in complex interactions, such as predator interference, cannibalism, parasitoid avoidance behavior, and intraguild interactions [6,10,11,12,13]. In such cases, the heterospecific interactions among the foraging enemies may reduce their per capita search activity and attack efficiency at a given host density. Few studies included the consequences of these interactions on the control efficiency of natural enemies when sharing the same resources in multiple enemy systems [14,15]
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