Individual study: Hedgerows enhance beneficial insects on adjacent tomato fields in an intensive agricultural landscape
Morandin L.A., Long R.F. & Kremen C. (2014) Hedgerows enhance beneficial insects on adjacent tomato fields in an intensive agricultural landscape. Agriculture, Ecosystems & Environment, 189, 164-170
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Pest regulation: Plant hedgerows
A replicated, paired, site comparison in May–August 2009–2010 in tomato fields in the Sacramento Valley, California, USA, found that a higher proportion of pest egg were parasitized in fields with hedgerows, compared to fields with weedy edges, but only up to 100 m into the crop. Similar levels of fruit damage were found in fields with and without hedgerows. Fewer pests were found in fields or field edges with planted hedgerows, compared to fields or field edges without hedgerows. Pest regulation: Parasitism of stink-bug Euschistus conspersus eggs (a tomato pest) was higher in fields with hedgerows than in fields with weedy edges, 0–100 m but not 200 m into the crop (0 m: 0.19 vs 0.11 proportion of eggs parasitized; 10 m: 0.30 vs 0.18; 100 m: 0.20 vs 0.10; 200 m: 0.15 vs 0.11). Crop damage: Similar amounts of fruit damage by pests were found in fields with hedgerows or weedy edges (amounts of damage not reported). Pest and natural enemy numbers: In sweep-net samples, fewer pests, but not significantly fewer predators or parasitoids, were found in hedgerows than in weedy edges (pests: 2 vs 20 individuals/sample; predators: 6 vs 6; parasitoids: 6 vs 2). In shake samples, more predators (10 m: 0.25 vs 0.05 predators/sample; 100 m: 0.15 vs 0.05; 200 m: 0.30 vs 0) and fewer aphids (10 m: 0.21 vs 0.32 proportion of leaves with aphids; 100 m: 0.14 vs 0.23; 200 m: 0.11 vs 0.21) were found in fields with hedgerows than in fields with weedy edges. In sticky-card samples, more parasitoids, but not more predators, and fewer pests were found in hedgerows than in weedy edges; more parasitoids were found in fields with hedgerows than in fields with weedy edges, up to 100 m into the crop, and fewer pests were found in fields with hedgerows than in fields with weedy edges, up to 10 m into the crop (number of individuals not reported). Methods: Native perennial shrubs (305–550 x 7 m), bordered by native perennial grasses (3 m), were planted in 1996–2003 on the edges of six fields (hedgerows) and compared to the unplanted edges of six fields (weedy edges). Invertebrates were sampled four times/year using sweep nets (40 cm diameter; six sweeps/edge) and sticky cards (7.6 × 12.7 cm; six cards/edge and six cards/crop), and by shaking plants (late May only). Stink-bug egg masses were exposed for five days in early July on the undersides of leaves.