Intraguild predation (IGP) -the predation of a natural enemy species upon another one sharing a prey species -is relatively frequent in both natural and agro-ecosystems. This may reduce pest control and the establishment of predator populations during mass release of biological control agents or in multi-predator systems due to increased mortality of predators. IGP is exacerbated in isolated and space-limited systems such as greenhouses, due to reduced food resources and movement. Therefore, adding food resources as an alternative to the main prey, such as floral resources, c ould reduce IGP between natural enemies in these systems. In the present study we investigated the role of supplemental floral resources to help reduce intra-and interspecific IGP involving Harmonia axyridis and Propylea japonica (Coleoptera:

Banker plant systems can be used to sustain a reproducing population of biological control agents (BCAs) within a crop, thus providing long-term pest suppression. The founder population of natural enemies in banker plant systems is usually mass-reared on factitious hosts. Thus, a better understanding of the population fitness and pest control performance of mass-reared BCAs in the field is crucial when developing integrated pest management (IPM) strategies. In this study, we determined the fitness of the generalist predator, Chrysopa pallens (Hemiptera: Chrysopidae) ever cultured on different food sources (i.e., mass rearing food, Corcyra cephalonica eggs, and aphid food, Megoura japonica) preying on Aphis craccivora in a banker plant system in a greenhouse based on Chi’s age-stage, two-sex life table analysis method. The life tables and predation rate parameters of C. pallens were not significantly different between both treatments under fluctuating temperature conditions. Corcyracephalonica eggs did not significantly weaken the performances of C. pallens in a Vicia faba–A. craccivora banker plant system compared to aphids. In conclusion, C. cephalonica eggs can be used for the mass production of C. pallens as the founder population in a banker plant system. Moreover, linking the life table data with the predation rate is an effective strategy for evaluating mass rearing programs in establishing banker plant systems.

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Banker plants increase biological pest control by supporting populations of non-pest arthropod species, used as alternative hosts or prey by natural enemies. Due to the specificity of trophic interactions, banker plants may not efficiently promote natural enemies with different ecologies. Yet in most cropping systems, different pest species are present together and require different biocontrol agents to efficiently control them. In the present study, we tested the combined use of two banker plants and their associated prey/host to enhance populations of the specialist parasitoid Encarsia formosa targeting the main tomato pest Bemisia tabaci, and a polyphagous ladybird Propylea japonica targeting the secondary pest Myzus persicae in tomato crops. In a laboratory and a greenhouse experiment, we measured the abundances of these four species using the Ricinus communis-Trialeurodes ricini banker plant system alone, in combination with the Glycines max-Megoura japonica system, or in absence of banker plants. We found that the first banker plant system enhanced populations of E. formosa, resulting in increased suppression of B. tabaci populations and the suppression of their outbreak in both our laboratory and greenhouse experiment. Conversely, abundances of P. japonica were not affected by this first system, but were significantly increased when the second was present. This resulted in increased control of M. persicae populations and the suppression of their early and late outbreaks. Our study demonstrates the potential for combined banker plants to provide long-term, sustainable control of multiple pests by their target natural enemies in complex agroecosystems. KeywordsAlternative prey • Bemisia tabaci • Biocontrol agent • Competition • Encarsia formosa • Functional plant • Myzus persicae • Propylea japonica • Secondary pest Key message • Multiple pest species are present simultaneously in cropping systems, requiring multiple natural enemies. • Multiple banker plants are needed to support populations of biocontrol agents with contrasted ecologies.Communicated by Cesar Rodriguez-Saona.Xu Chen and Coline C. Jaworski equally contributed to this study.

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