| FARMLAND ECOLOGY - QUESSA
Sentinel system to measure aphid predation
comprised of live cereal aphids attached to cards. © John Holland/GWCT
Figure 2 a) location of grasslands (moss green), wheat
(brown) and roads (grey) in a landscape sector in the UK and b) heat map of the predicted predation rates on cereal aphids ranging from
very low (blue tones) to low (red tones). (Maps produced by Marjolein Lof and Wopke van der Werf at Wägeningen University)
of blowfly, fruit fly pupae, moth eggs and cereal aphids, along with two species of seed (fat hen and rough-stalked meadow-grass) known to be consumed by ground beetles. These were placed either on the ground or on the crop according to the pest they were meant to represent, in each focal field along two transects extending up to 70 metres from the SNH. The average level of predation was higher for the sentinels with insect prey on the ground (37-53%) compared with on the crop (12-22%) or for the seeds (4-8%) (see Figure 1). The proportion of herbaceous habitats in the landscape had a positive effect on predation of three sentinel types, whereas woody habitats sometimes had a negative effect. Natural cereal aphid infestations decreased as the proportion of all SNH increased in the landscape. The type of SNH in the adjacent boundary had relatively little impact. Predation of larvae and seeds increased with distance from the SNH because this was predominantly by the larger carabid beetles that reside permanently within fields and derive no benefit from field margin habitats. Maps also revealed that some habitats including crops benefited overall levels of pest control and that there was considerable variation across the landscape (see Figure 2). We conclude that high levels of natural pest control can occur, but there is potential to improve this by introducing more herbaceous habitats into the landscape and to encourage predators that forage on the crop itself.
Soil carbon Soil samples were taken within each SNH type and crop fields and the amount of carbon calculated from the levels of soil organic matter. Fields averaged 127 tonnes of carbon per hectare (t C per ha), herbaceous linear habitats 172 t C per ha, woodland
60 | GAME & WILDLIFE REVIEW 2016
www.gwct.org.uk
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