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 · 10 3 aphid days per m 2 , 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/m 2 (L) vs. 5.4 PU/m 2 (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/m 2 ) and individual predator fractions (individuals/m 2 ) and absolute rates of aphid density increase (individuals/m 2 ) 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/m 2 . 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.
Syrphid larvae as well as adults and larvae of Propylaea 14-punctata (L.) and Coccinella 7-punctata L. are the most dominant aphid predators in winter wheat of Middle and Eastern Germany. The aphid-coccinellid interaction was investigated in a 4-year project aimed at the definition of beneficial thresholds (density of a predator guild necessary to keep a pest under control) for these species. Eight field studies and four cage experiments were performed to calculate the infestation reducing effect of coccinellids, particularly C. 7-punctata. The obtained data were used to estimate beneficial thresholds for the whole predator complex and especially for coccinellids whereby all predators have been converted into predator units (PU), e.g. fertile female of C. 7-punctata = 1.00 PU, larva = 0.33 PU, Episyrphus balteatus larva = 0.46 PU. In the field studies the calculation of the coccinellid related effect within the antagonist potential has not yet succeeded. The cage experiments have to be seen as case studies under special conditions. Therefore activities concentrated on the improved and validated simulation model GTLAUS including the submodels COCCISEP and WHEAT. Simulation runs with this tritrophic interaction model including the field count and cage trail data have shown that the beneficial threshold of C. 7-punctata to control cereal aphids under average conditions in Middle and Eastern Germany varies likely between 8 and 20 PU/m2. However, an isolated evaluation of C. 7-punctata or another single predator species within the beneficial potential is undoubtedly not realistic. It seems to be better to calculate summarized effects of the whole predator community weighted as PU.
Zusammenfassung Bestimmte gefährliche Schadorganismen sowie mit ihnen befallene Pflanzen dürfen in die Europäische Gemeinschaft nicht eingeführt und auch nicht innerhalb der EG verbracht werden. Das Arbeiten mit diesen Schadorganismen ist ebenfalls untersagt. Für Forschungsund Züchtungszwecke können unter bestimmten Voraussetzungen von diesem Verbot Ausnahmen gemacht werden. Wissenschaftliche Einrichtungen können diese Ausnahmen bei dem zuständigen Pflanzengesundheitsdienst beantragen. Das Antrags-und Genehmigungsverfahren ist auf der Grundlage der EG-Richtlinie 95/44/EG geregelt. Der Import, das Verbringen oder das Arbeiten mit Schadorganismen oder befallenen Pflanzen kann nur zugelassen werden, wenn eine Einschleppung oder Ausbreitung dieser gefährlichen Schadorganismen verhindert wird. Zu diesem Zweck werden strenge Quarantäneauflagen durch den örtli-chen Pflanzengesundheitsdienst erteilt. Das Verfahren wird am Beispiel des Imports von Malus-Reisern beschrieben.Schlüsselwörter Gefährliche Schaderreger · Import · Innergemeinschaftliches Verbringen · Quarantäne · Forschung · Züchtung · RL 95/44/EG M. Möwes (u) Sächsische Landesanstalt für Landwirtschaft, Referat Pflanzengesundheit und Diagnose, Abstract Specific harmful organisms whether singly or associated with plants shall not be introduced into the European Community. All activities which would involve these organisms are not allowed. The authorities can make under defined requirements an exception for activities for trial or scientific purposes and for work on varietal selections. The responsible body has to determine conditions which must be satisfied in the case of introductions, movements or activities, in order to ensure that there is no risk of harmful organism spreading. The legal basis is the Commission directive 95/44/EC transferred into German legislation by the Pflanzenbeschauverordnung.Keywords Harmful organisms · Import · Quarantine · Movement within the community · Research · Breeding · Commission-Directive 95/44/EC
Tiller counting or total plot harvest -how exact are predator counts in winter wheat?Methodical investigations on predator recording in winter wheat were performed at 3 sites in Middle Germany (Flaeruing, Magdeburger Boerde, Middle German dry region near Halle/S0 in 1994 to 1996. In 13 field studies tiller counts (5 x 6 m drill row with corresponding soil surface) were compared with the total plot harvest (an ,,absolute method", combination of D-VAC suction sampling and vegetation harvest within a I m 2 -cage, laboratory determination of arthropods).The U-test analysis of each survey according to MANN and WHITNEY shows only 8 significant differences in 55 comparisons. There were no clear trends. Considering the average predator densities in 13 investigations, the following relative densities (and significances using t-test) were calculated for field counts in comparison with the total plot harvest: coccinellid adults -0.88 (P>0.10), coccinellid larvae -0.88 (P>0.10), syrphid larvae -0.92 (P>0.10), chrysopid larvae -0.84 (P>0.10), adult carabids -0.24 (P=0.054), adult staphylinids -0.14 (P=0.002) and adult spiders -0.48 (P=0.058). The important underestimation of polyphagous predatory arthropods in field counts is discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.