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

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.

Composition and Food Web Structure of Aphid-Parasitoid Populations on Plum Orchards in Chile

“…Moreover, at least seven parasitoid species found on plums in the present study, have also been reported attacking aphid species on the cereal crops, including A. platensis (previously reported in Chile as Aphidius colemani , [ 58 ]), L. testaceipes , P. volucre , A. avenae , A. ervi , A. matricariae and D. rapae [ 71 , 78 ]. Similarly, a previous study carried on plum orchards found that the main parasitoid species attacking cereal aphids was A. platensis [ 79 ]. However, in relation to the second hypothesis, we did not observe a higher connectance (possible links for each host–parasitoid pair species) on the SV than on the OCC treatment, despite the increased species richness of parasitoids in the food web for the SV treatment.…”

Effect of Vegetational Diversification on the Gene Flow of Natural Enemies in a plum orchard

“…The bottom-up effects from the habitat diversi cation into studied cropping systems on the richness and/or abundance of natural enemies, as well as hostnatural enemy multi-trophic interactions, are well recognized (Han et al 2022), however, its impact and mechanisms underlying biological control and natural parasitism are still less understood. Among the habitat management strategies, winter cereal cover crops can improve natural enemy habitats by providing additional insect hosts, food sources, shelter, and/or breeding habitats for natural enemies like parasitoid wasps during winter (Lérault et al 2022).…”

“…The parasitoid individuals of the species Aphidius platensis were collected by sampling live aphids from common aphid species on plum trees (Prunus domestica) intercropping with oat cover crops during the growing mid-season spring (October-December 2018) in an organic plum tree orchard located inside the farm "Alto Las Delicias" near the city of Rancagua, in the O'Higgins region of central Chile (34_08007.600 S, 70_38059.500 W) (Lérault et al 2022). The central Chilean valley has a temperate Mediterranean climate, with dry summers and mild and rainy winters.…”

“…Enhancing the local farm biodiversity can improve ecosystem service supply, by providing overwintering shelter and alternative food resources for natural enemy populations (Gurr et al 2017;Gontijo 2019). In diversi ed crop habitats, natural enemies such as parasitoid wasps could be favored by additional host species and non-host resources such as nectar, ower, and honeydew (Lérault et al 2022). Habitat management strategies that increase vegetational diversity by adding cover crops in between cultivated trees in orchards, and intercrops, as well as by allowing the growth of spontaneous vegetation around the target crop plants could provide optimal conditions for the temporal synchronization of key natural enemies and their pest-hosts (Tschumi et al 2015;Segoli et al 2020;Möller et al 2020).…”

“…In previous studies, we showed that by adding a ground oat (Avena sativa) as a winter cover crop in between cultivated plum trees in orchards (Prunus domestica), it is possible to provide food and alternative hosts for aphid parasitoids (Hymenoptera: Braconidae) (Alvarez-Baca et al 2020, 2022; Lérault et al 2022). Aphid parasitoids are widely utilized in the biological control of economically important aphid pests, providing signi cant control of these in many countries of the world (Hulle et al 2020).…”