Open Access

Christa Volkmar, Camilla Werner, Peter Matthes

• Zu den Ährenschädlingen am Winterweizen zählen die Gelbe Weizengallmücke (C. tritici (Kirby)) und die Orangerote Weizengallmücke (S. mosellana (Géhin)) (Holland & al., 1996). In Abhängigkeit vom Befallsstadium der Weizenähre und der Biologie der Erreger sind folgende Schadsymptome bekannt: Verminderung der Kornzahl pro Ähre (C. tritici) bzw. geschrumpfte oder missgebildete Körner (S. mosellana) (Mölck, 2006). Der Saatgutwert wird beeinträchtigt und die Backqualität beeinflusst (Miller & Halton, 1961). Hinsichtlich Prognose und Überwachung des Auftretens von Weizengallmücken gab es bisher keine praxistauglichen methodischen Ansätze im Bundesland Sachsen-Anhalt. Hinzu kommt, dass der derzeit verstärkt praktizierte pfluglose Anbau von Weizen nach Weizen ein höheres Befallsrisiko erwarten lässt. Mit der Identifikation von Sexualpheromonen, die als hoch attraktiv für Männchen von S. mosellana gelten (Gries & al., 2000), eröffnen sich nun neue Prognosemöglichkeiten. Die effektive Nutzung von Pheromonfallen zum Monitoring von Gallmücken könnte somit ein erster Baustein zur Erarbeitung praxistauglicher Richtwerte darstellen. In einer zweijährigen Testphase wurde in Zusammenarbeit mit der Landesanstalt für Landwirtschaft, Forsten und Gartenbau geprüft, ob die Pheromonfallen eine Gradationswahrscheinlichkeit der Problemschädlinge, insbesondere in Risikofruchtfolgen signalisieren können. Die Ergebnisse sowie Daten zu weiteren Überwachungsansätzen werden präsentiert.
• Lemon wheat blossom midges (Contarinia tritici) and Orange wheat blossom midges (Sitodiplosis mosellana) (Diptera: Cecidomyiidae) belong to the most prominent insect pests in winter wheat (Holland & al., 1996). However, no practical method exists to predict or monitor the impact of these insect pests. There is also a lack of recent research on the issue particulary for Central Germany (older studies include: Lübke & Wetzel, 1984, Volkmar & 1989). Consequently, this study attempts to provide new data on the occurrence, monitoring and crop damage of wheat blossom midges. It also focuses on the impact of changing agricultural conditions such as wheat-to-wheat crop rotation, reduced soil tillage or different crop variants. A systematic survey of midge occurrence and crop damage in a wheat-to-wheat crop rotation was carried out at a research field (variants: Elvis, Altos in 2005) and conventional winter wheat fields in 2006 (variant Tommi). S. mosellana were monitored by means of pheromone traps. In 2006, white traps were tested as an alternative method to collect data on S. mosellana and C. tritici. Flight activity of adult midges was monitored on 13 different dates (Tab. 1). Crop damage was evaluated on 8 dates (Tab. 2). A total of 50 spikes per variant and date were randomly selected for microscopical examination. The analysis included parameters such as number of larvae per infested seed, number of corn thrips (larvae and adults) per spike or number of infested seeds per spike. In 2005, the activity of adult S. mosellana reached its peak in the phenological growth stage of full flowering (BBCH 65-69). The activity density was higher in the Elvis variant with 260 midges per trap (monitoring until mid-flowering) as compared to the Altos variant with 89 midges per trap (monitoring until the end of flowering period). In 2006, the activity of adult S. mosellana reached its peak in BBCH 51 (beginning of heading) with 246 midges per trap (Tommi variant). In 2005 the highest abundance of larvae per ear was established for BBCH 75 with an average of 2.1 (Altos) and 1.6 (Elvis). In 2006 these numbers were significantly higher. In the Tommi variant, an average of 14.3 larvae per ear was reached during BBCH 70-73. The ratio of midge-damaged kernels was evaluated in 2005 on BBCH 80-85 with 6.3 % (Altos) and 4.4 % (Elvis), while in 2006 a ratio of 23.5 % was reached in the Tommi variant. The results suggest that the intensity of crop damage depends on the correlation of two factors. The closer the activity peak of midges correlate with the sensitive wheat growth stage of heading (BBCH 50-59), the higher the crop damage. This is highlighted by the results of 2006 in the Tommi variant. In other cases, S. mosellana reached its activity peak much later (in 2005 during BBCH 65-69, resp. in 2006 on BBCH 73-75) and the ensuing crop damage was significantly smaller. In conclusion, the results of this survey in Central Germany stress the influence of changing agricultural conditions and regional cultivation concepts. They also recommend further studies that cover several years in open habitats.