Abstract
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.
Highlights
The trophic resources of most living organisms are heterogeneously distributed in time and space [1]
We evaluated whether intercropping in a plum tree orchard could provide both types of trophic resource needed by parasitoids: early alternative host aphids through intercropping with cereals, and extrafloral nectar with late alternative host aphids through intercropping with legumes
The collected aphids that turned into mummies belonged mainly to the species Rhopalosiphum padi in oats, mostly present at the beginning of the season, and later on to the species Acyrthosiphon pisum
Summary
The trophic resources of most living organisms are heterogeneously distributed in time and space [1]. Regardless of the spatial or temporal scale considered, the resources used by an organism vary in diversity and abundance, and their distribution influences the organism’s behavior [2]. For aphid parasitoids such as Aphidiinae [Hymenoptera: Braconidae], whose adults lay eggs in aphids and can feed on various carbohydrate sources, aphid hosts and carbohydrates are two essential and complementary trophic resources [3,4]. The availability of aphid hosts in cropping systems varies throughout the year in temperate regions. Parasitoids are active as biocontrol agents especially during the warm season, when pest aphid populations start to grow within the crop
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