Providing Alternative Hosts and Nectar to Aphid Parasitoids in a Plum Orchard to Determine Resource Complementarity and Distance Range Effect on Biological Control

There are many different practices that contribute to conservation biological control, but little is known about their complementarity. We tested the effects of providing food and alternative hosts to parasitoids by intercropping a plum orchard with companion plants. Oats and vetch were intercropped into the orchard either as single-species (oats or vetch) or two-species (oats and vetch combined) intercrops within an inter-row. The trophic resources provided by these intercrops were assessed, along with the incidences of aphids and their parasitoids in plum trees. We found up to ten alternative host species provided by oats and vetch, and extrafloral nectar was available from the vetch and mixed strips. An effect of intercrop type and distance to plum trees was observed on aphid incidence during one sampling period. Parasitism rates in exclusion cages were affected by intercrop type, reaching almost 60% close to the mixed intercrop. However, no general tendency was observed upon whether oats, vetch or their mixture was associated with a lower incidence of aphids. We found no evidence that providing effective sources of food and alternative hosts for parasitoids increased aphid mortality in this study. The context-dependent efficiency of intercropping is discussed.

Automated summary

This study tested the effects of intercropping with companion plants on aphids and their parasitoids in a plum orchard. The results showed that intercropping provided multiple alternative host species and extrafloral nectar, but there was no general association between intercrop type and aphid incidence. The study suggests that providing effective sources of food and alternative hosts for parasitoids does not increase aphid mortality.