The potential of predators in natural control of aphids in wheat: Results of a ten-year field study in two German landscapes |
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Authors: | B Freier H Triltsch M Möwes E Moll |
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Institution: | (1) Institute for Integrated Plant Protection, Federal Biological Research Centre for Agriculture and Forestry, Stahnsdorfer Damm 81, 14532 Kleinmachnow, Germany;(2) Data Processing Group, Federal Biological Research Centre for Agriculture and Forestry, Stahnsdorfer Damm 81, 14532 Kleinmachnow, Germany |
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Abstract: | In the present study, we investigated the natural control of aphids by predators in wheat fields in a low (L) and high-input
cropping region (H) of Germany during a 10-year period. Data for the statistical analyses were obtained from weekly after
the start of aphid emergence. The mean annual aphid indices, calculated as the sum of Sitobion avenae (Fabr.), Rhopalosiphum padi (L.), Metopolophium dirhodum (Walk.)(Homoptera: Aphididae), were 30.4 and 81.5 × 103 aphid days per m2, for L and H, respectively. Nine predator fractions
were analysed: Coccinella septempunctata L., adults (1) and larvae (2), Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae) adults (3) and larvae (4), syrphid larvae (mostly Episyrphus balteatus De Geer] (Diptera: Syrphidae)) (5), Chrysoperla carnea Steph. (Neuroptera: Chrysopidae) larvae (6), and adult carabids (7), staphylinids (8) and spiders (9). The two sites were
comparable in terms of the mean size of the overall predator community, expressed in predator units (PU): 4.9 PU/m2 (L) vs.
5.4 PU/m2 (H). Most predator fractions responded numerically to increasing aphid densities. The numerical response was strongest
in syrphid larvae, scarcely detectable in adult coccinellids, and virtually non-existent in epigeic arthropods. Multiple regression
models revealed indirect relationships between the weekly overall predator community densities (PU/m2) and individual predator
fractions (individuals/m2) and absolute rates of aphid density increase (individuals/m2) one or two weeks after baseline.
A site-independent reduction of the aphid density increase to nil (y = 0) was observed at 3.9 to 4.2 PU/m2. Consequently,
the 2.7 times higher aphid density at H cannot be attributed to the presence of fewer predators or lower effects of the overall
predator community or of any individual predator fraction. |
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Keywords: | Aphids Coccinellids Coccinella septempunctata Natural control Propylea quatuordecimpunctata Syrphids Wheat |
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