The effects of wildflowers in apple orchards on pollination and pest regulation services

McKerchar, Megan (2016) The effects of wildflowers in apple orchards on pollination and pest regulation services. PhD thesis, University of Worcester.

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Abstract

Due to an increasing human population coupled with changing food demands, agricultural methods have increasingly intensified. Pollinators in the UK are declining which has been partially linked to habitat loss due to agricultural intensification. This demonstrates a need for sustainable agricultural intensification, using methods that will promote biodiversity while maintaining or enhancing crop yields. Wildflowers have been shown to enhance pollinators, natural enemies and the services they provide in various crop systems, but seldom studies looked at both pollination and pest regulation services on a large scale. This study examined the effects of wildflowers on these ecological services in intensive apple orchards, using a replicated split-plot
design on a one-hectare scale. Experiments were conducted over three years on two apple cultivars c.v. Jazz and c.v. Braeburn, where the first year represented baseline
data.

Results showed that bumblebees (Bombus spp.), solitary bees (especially Andrena spp.) and managed honeybees were the most frequently observed pollinators of apple
blossoms. Pollinator visitation was not significantly different in the wildflower plots, however there was a general trend of increased visitation in the wildflower plots where plots had good wildflower establishment. Fruit yield and size were positively affected
by increased pollination, where hand pollination was greater than insect pollination, which was greater than insect excluded pollination. Insect pollination was
economically important for both Jazz and Braeburn, and Braeburn did not demonstrate pollination deficits. Production deficits in Jazz partially due to pollination, was highly variable between plots and years, ranging from £3,334 to £6,497per hectare.

Mixed results were found for the effects of the wildflowers on natural enemies within the trees. There was a significant increase in abundance of aphidophagous predators in year two, and significantly more Theridiidae spiders but fewer Araneidae spiders in year three. Cumulative toxicity of insecticides and acaricides used was associated with a decreased abundance of natural enemies, which possibly confounded further effects
of the wildflowers. In year three, significantly fewer rosy apple aphids and ants were recorded in the trees in the wildflower plots, but the number of trees infested was unaffected. There was no effect of wildflower presence on the abundance of woolly apple aphid during all years of study.

The cost of sowing the wildflowers is recovered within the first two years of the orchards life due to savings from reduced mowing. Therefore, using wildflowers to
enhance pollinators and natural enemies in apple orchards is recommended, due to the short and long term economic and ecological benefits shown in this study.

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