Study on the sensitivity of three oat varieties to the saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae)

Saddle gall midge, Haplodiplosis marginata (von Roser) is a univoltine pest of cereals which occurs in Europe. The larvae overwinter in the soil. During the spring, the new emerged females lay eggs on the leaves of cereals and grasses. After hatching, larvae migrate under the leaf sheath, where they develop at the expense of the plant. As a reaction, stems induce saddle-shaped galls of 5 to 10 mm long. Numerous galls can lead to stem breaks and important yield losses when they are numerous.
After 40 years without any reporting, large populations of H. marginata and important damage have been observed since 2010 in wheat crops in Belgium, especially in the Flemish Polders where clay soils and intensive farming of cereals favour heavy infestations.
According to some research conducted in the 60s during the last outbreak, oat (Avena sativa L.) is known to be one of the less attractive hosts to the saddle gall midge. Our study was thus performed in order to assess the host sensitivity of three oat varieties currently grown in Belgium (Evita, Effektiv and Freddy).
Therefore, oat varieties were sown on infested ground in two separate enclosures in a glasshouse. In the first enclosure, only the three oat varieties were grown ; in the second one, these three oat varieties were grown together with two varieties of spring wheat (Granny and KWS Chamsin). Two parameters were measured: the percentage of leaves with laid eggs, and the number of galls per stem.
The percentage of leaves with eggs showed that the infestation is significantly lower on oats when they are in presence of wheat. The infestation was also significantly higher on wheat than on oat, which means oat is a much less favoured host plant than spring wheat for laying. Oat varieties were significantly different regarding the number of galls per stem, but with very little damage compared to wheat. The Freddy variety even seemed to be completely resistant to saddle gall midge, as no galls were observed although there were a similar percentage of leaves with eggs for the three oat varieties. Cropping oat could thus contribute to reduce or even to eliminate infestations of H. marginata.