The expanding oilseed rape insect pest community in Estonia

Abstract: The increase in oilseed rape cultivation over the last two decades has led to the introduction of a “new” pest to Estonian farmers. The brassica pod midge, Dasineura brassicae (Winnertz, Diptera: Cecidomyiidae) is a pest of potential economic importance in Europe. Its presence in oilseed rape fields in Estonia became clear during a study conducted to measure the number of overwintered oilseed rape pests and hymenopteran parasitoids within fields and in field edges. Soil samples were collected and incubated in emergence traps from different fields that grew winter oilseed rape in the previous year in Tartu County. Only a low number of pests emerged from these samples from which we can assume that despite the widespread opinion amongst Estonian farmers, most pests do not stay in or near the fields for overwintering. However, the most abundant pest collected was the brassica pod midge, indicating that it does prefer to stay in or near the fields for winter. Additionally, significantly more parasitoids emerged than pests indicating that these natural enemies also chose their overwintering sites within or near the fields. Hence, minimal tillage and a well-planned, diverse crop rotation of at least five years should be favoured to lower the threat of this relatively new pest.