A few biological specificities of the carrot root fly (Psila rosae Fabre) for a more accurate forecasting in carrot (Daucus carota L.) production

In France, as in northern Europe, the carrot fly (Psila rosae Fabre) is the most important pest of Apiaceae crops, principally for carrots but also for celeriac, parsnips, parsley. This pest takes on a new importance with the reduction of active ingredients available to growers for crop protection and the absence of good alternatives easily usable by growers. Research is being conducted on risk forecasting models, in particular the German model SWAT. Unfortunately, SWAT does not yet allow a suitable forecast of the risks: the first flight is predicted too early under the conditions of southwest France but also in the west, the flight predicted for June-July is generally not observed in the south, and the third flight is predicted too early. Firstly, we have observed that in the south and west of France the overwintering form is larvae and not pupae like in the more northern zones. Secondly, pupal estivation is not really taken into account by the model explaining the difficulty to have a reliable forecast for the last flight. With the strong thermal amplitudes observed in southwest France, it is necessary to take into account the values of maximum temperatures after the first flight for the evaluation of the second flight, which occurs in autumn.