Unusual occurrence of cocoons in population of Haplodiplosis marginata (Diptera: Cecidomyiidae) in Belgium.

The saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae), is a phytophagous species that develops in saddle-shaped galls on stems of wheat Triticum vulgare, barley Hordeum sativum, rye Secale cereale, and some other species of Poaceae. Only one generation develops per year. Full-grown larvae leave galls and drop onto the soil where they remain up to the springtime of the following year. Larvae do not usually spin cocoons. However, formation of cocoons by larvae was observed in populations developing in western Europe: in England in 1954, in the Netherlands in the 1960s, and in Belgium in 2011. On the basis of our analysis, a part of the larval population forms cocoons as protection against unfavorable weather conditions, especially drought.

Study on the sensitivity of three oat varieties to the saddle gall midge, haplodiplosis margina ta (von Roser) (Diptera: cecidomyiidae).

The saddle gall midge, Haplodiplosis marginota (von Roser, 1840) is a univoltine pest of cereals which occurs in Europe. The larvae feed on stems and attractive saddle-shaped depressions, driving to important yield losses when the galls 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 1960s during the last outbreak, oat (Avena sativa L.) is known to be one of the less favourable hosts to the saddle gall midge. Our study was 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 soil 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 was significantly lower on oats when they were in presence of wheat. The egg infestation was also significantly higher on wheat than on oat, which means oat is a much less favourable host plant than spring wheat for egg laying. Oat varieties were significantly different from each other 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 was a similar percentage of leaves with eggs for the three oat varieties. Cropping oat could thus contribute to reduce infestations of H. morginato.

Chemical control of Haplodiplosis marginata von Roser (Diptera: Cecidomyiidae).

The saddle gall midge, Haplodiplosis marginata (von Roser), has been detected in Belgium since 2010, after several decades without any reporting. It had indeed caused serious damages between 1965 and 1970. This insect is a European cereal pest whose larvae feed on stems and engender saddle-shaped depressions, resulting in yield losses. Face with the resurgence of this pest, it was decided to study its spatial distribution and, because serious damages were observed in some regions, to develop effective curative control. To date, chemical protection seems to be the only immediate solution in case of heavy emergences. Experimentation was conducted in a highly infested field (Meetkerke, Belgian Polders), according to a randomized complete blocks arrangement with four replications. Foremost, a lambdacyhalothrin-based insecticide was used to evaluate efficiency of several protection schemes, ranging between one and four spray(s). The large spread of flights observed during the 2011 spring allowed to highlight the effect of treatment date on the attack intensity and also on the galls distribution along the stem, on the different internodes: the lower internodes were protected by the early sprayings, while last sprayings induced reduction of galls number on the upper internodes. Moreover, several insecticides already registrated in cereals against aphids were compared for their efficacy against saddle gall midge. Studied pyrethroids have shown a very good efficacy, ranging between 75% and 87%, when applied twice with a 2 weeks interval. To be efficient, insecticide applications must thus be synchronized with the flights and egg-laying periods. Monitoring the phenology of flights is thus essential as part of integrated pest management against saddle gall midge.