Influence of a flower strip and a hedgerow on the functional biodiversity in a Tilia cordata nursery: Do they have an effect on the occurring mite community?

Traditionally, insects and mites in Belgian tree nurseries have been controlled by pesticides. However, due to the recent withdrawal of several pesticides and the application of the EU directive 2009/128/EC, there is an urgent need for alternative control methods. One possible strategy is conservation biological control, aiming to stimulate control by endemic natural enemies. Providing adjacent natural habitats such as flower strips and hedgerows can encourage population buildup of natural enemies and, subsequently, their spread into crop fields. In this context we investigated the impact of a bordering native flower strip and hedgerow on the population density of several key pests and their natural enemies in an unsprayed lime tree (Tilia cordata) nursery. Lime aphid, sawfly and rust mite (Aculus ballei) were found in high numbers in 2011 and therefore these pests were further studied. We report the results related to the mite community found during 2011-2012. Leaves (during growing season) and twigs (during winter period) were sampled, extracted and quantified every fortnight to monitor population dynamics of A. ballei. In addition, other Acari were extracted monthly using the Berlese funnel technique. Extracted species belonging to Phytoseiidae, Tydeidae and Tetranychidae were counted and identified to species level. There was a significant difference in occurrence of A. ballei between both years, however this was not due to an effect of the flower strip or hedgerow. Tetranychidae were more abundant in control plots than plots bordered by flower strips or hedgerows, however there was no statistical difference. The adjacent flower strip had an increasing effect on the population densities of both Phytoseiidae and Tydeidae, however again this could not be proven statistically. The hedgerow didn’t affect any mite species. In addition, eight Phytoseiidae species were found on Tilia during the sampling period, of which Euseius gallicus is new for the Belgian fauna.