Apple aphid, Aphis spp. (Hemiptera: Aphididae), and predator populations in an apple orchard at the non-bearing stage: The impact of ground cover and cultivar

Bruno Fréchette,Franz Vanoosthuyse,Éric Lucas,Gérald Chouinard,Daniel Cormier

doi:10.14411/eje.2008.069

Abstract

A two-year field experiment was conducted to determine whether a conservation biological control strategy could be applied to enhance the biological control of green apple aphids, Aphis spp., in a high-density and scab-resistant apple orchard at the non-bearing stage. The natural occurrence of aphid predators and their impact on aphid populations were evaluated in 2005. The impact of predation on aphid densities was evaluated by comparing a predator exclusion treatment with a control. In 2006, the possibility to enhance predator abundance/performance and aphid biological control with a flowering ground cover was tested: trees were grown either with a flowering ground cover of phacelia, Phacelia tanacetifolia Bentham, and buckwheat, Fagopyrum esculentum Moench, or with a conventional ground cover of mixed Poaceae species. In 2006, it was also determined whether aphid densities differ between Liberty and Topaz, 2 scab-resistant cultivars. Results indicate that the predatory arthropod community was dominated by Coccinellidae, Cecidomyiidae, and various spider species. The ladybird community was dominated by the exotic species Harmonia axyridis Pallas, and the abundance of this species was correlated with aphid density. Naturally occurring predators had little impact on aphid abundance, although the proportion of trees with aphid colonies was greater in the predator exclusion treatment on two consecutive dates in 2005. Ground cover types had no impact on aphid densities. The oviposition response of Cecidomyiidae to aphid density was greater in Liberty trees with flowering ground cover than with the conventional ground cover. Conversely, the response of ladybird adults to aphid density was more important in Topaz trees with the conventional ground cover than with the flowering ground cover. Finally, no difference occurred in aphid abundance between Liberty and Topaz trees. Those results are discussed from a biological control and ecological point of view.

Highlights

In Eastern North America, the most common aphid species in apple orchards are the green apple aphid, Aphis pomi de Geer and the spirea aphid, Aphis spiraecola Patch (Hemiptera: Aphididae)
This paper reports two trials performed in a young, high-density, and scab-resistant apple orchard
The first aimed at determining the role of naturally occurring foliage-dwelling predators in suppressing aphid populations, and the second explored the possibility of enhancing predator populations by growing a flowering ground-cover

Summary

Introduction

In Eastern North America, the most common aphid species in apple orchards are the green apple aphid, Aphis pomi de Geer and the spirea aphid, Aphis spiraecola Patch (Hemiptera: Aphididae). Those two species are hard to distinguish in the field and can be found in mixed colonies, and will be referred to hereafter as green apple aphids. The negative impact of green apple aphids is likely to be more important on young than mature trees (Kaakeh et al, 1992). Keeping their populations under damaging levels is important

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Results

Conclusion