Forecasting the emergence of the adult orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae) in Belgium

• The emergence of adult orange wheat blossom midges was monitored in Belgium.
• None of the existing emergence models give a reliable forecast across tested years.
• The relationship between rainfall and adult emergence is established.
• The factors defining inductive rainfalls are described.
• A new forecasting model of adult emergence is presented.

Agronomists often underestimate the damage inflicted by the orange wheat blossom midge, Sitodiplosis mosellana (Géhin), a wheat (Triticum aestivum L.) pest. The main risk arises when the emergence of the adult midges coincides with wheat ear emergence. The emergence of adult midges was monitored in Belgium over four years and analysed against climate data, establishing the significance of specific rainfall events as triggers for the final phase of development prior to emergence. This discovery, combined with experience from previous models, was incorporated into a new forecasting model, described in this paper. The new model consists of three separate phases. The first phase comprised a temperature accumulation of 250 degree-days (DD) above 3 °C, starting from 1 January. Once this initial condition is satisfied, the second phase starts, and it lasts until the occurrence of a double signal consisting of a rise in the mean daily temperature up to 13 °C, followed by rainfall. This rainfall event triggers an accumulation phase of 160 DD above 7 °C. Once this last condition is met, the adults emerge.