Different effects of aphid antagonists in wheat in two different landscapes and the consequences for integrated pest management - results of 10-year field studies

Freier, B.; Triltsch, H.; Mowes, M.; Gosselke, U.; Adisu, B.; Lee SangGuei

Bulletin OILB/SROP 26(4): 53-58

2003


ISSN/ISBN: 1027-3115
Accession: 003713078

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Abstract
Cereal aphids (such as Rhopalosiphum padi and Sitobion avenae) and their antagonists (including the predatory insects Coccinella punctata and Episyrphus balteatus) were counted in winter wheat fields in two different landscapes, Flaeming (F; a moderately fertile and well-structured region) and Magdeburger Boerde (M; a fertile and less structured region), in Germany, from 1993 to 2002 to analyse and compare their population dynamics. The mean level of aphid infestation was 124.3 aphid days per tiller in M, twice as high as in F (57.5 aphid days per tiller). The number of aphids exceeded the injury threshold (defined as 150 aphid days per tiller) in four of the ten seasons at M, but never in F. Surprisingly, the difference in infestation in the two regions did not appear to be influenced by predator occurrence since the densities of the predator communities, measured in predator units (PU) for eight weeks after wheat heading, were comparable (4.9 PU per m2 in Flaeming vs. 5.4 PU per m2 in M). The regional differences in infestation were more likely due to other factors, such as immigration rate and nutrient quality of the crop. Using the GETLAUS01 simulation model and the collected field data, we simulated the population dynamics of aphids and predators and the population dynamics without predator effects. Based on these simulations, the antagonist potential reduced the aphid numbers by a mean 198.3 (F) and 169.4 (M) aphid days per tiller. The relative effect of predators was also found to be higher in the less infested F than in M. We predict that 6.4 (F) and 2.6 (M) times more aphids would have occurred in the absence of predators. Accordingly, the incidence of damaging aphid infestation would have increased from zero to four years in F and from four to nine years in M. Therefore, although comparable numbers of predators were available for natural control, the predators were more effective in controlling the aphids in F. Despite the high predator levels, the aphids reached critical densities in M, but not in F. We therefore conclude that the use of an action threshold is necessary only in M.