Establishment potential of Diabrotica virgifera in the Netherlands
The establishment potential of Diabrotica virgifera (EPPO A2 quarantine pest) in the Netherlands has been investigated. It is recalled that in studies carried out in other European countries, it has been supposed that most mid and south-eastern European countries have suitable climatic conditions for the establishment of D. virgifera. In the Netherlands, the growing of maize became popular after the development of new cultivars and a stimulating EU legislation. The area increased from 77,000 ha in 1975 to 229,000 ha in 1994 (occupying one third of the Dutch arable lands, i.e. 7;% of the Netherlands surface). Maize is mostly cultivated on sandy soils in Noord-Brabant, Overijssel and Gelderland provinces.
Climatic data from 15 locations in the Netherlands and development models proposed by American scientists, have been used to assess the potential of the pest for establishment in the Netherlands. For comparison, calculations with climatic data from Hódmezövásárhely (an infested area in Hungary) have been included, and it is noted that these calculated data fitted very well with the situation observed in 1997. The following results (examples) have been obtained.
- Hatching of first larvae is expected around the: 29th June in Eindhoven (warmest location in the south), 15th July in Leuuwarden (in the north), compared to 19th May in Hódmezövásárhely (HU).
- 1st adults are expected around the: 3rd September in Eindhoven, 27th September in Leuuwarden, 8th July in Hódmezövásárhely (HU).
- 50% adult emergence is expected around: 13th October in Eindhoven, compared to 27th July in Hódmezövásárhely (HU).
In the Netherlands, maize ripes occurs in August or September, and the harvest is usually done around the 20th September. So even in the warmer places, emerging time of adults is later than harvesting time. In the northern part of the Netherlands, D. virgifera will have difficulties to find food, to complete its cycle and deposit eggs in the field (but may survive during very hot summers). In the south of the country, emergence will not be synchronized with maize flowering. However, it has been observed in the USA that populations were able to survive this asynchronization, but below economic levels. The authors pointed out that their calculations are preliminary, as only average air temperatures were used (and not soil temperatures). In addition, life parameters of D. virgifera may vary according to geographical regions and so far the exact origin of the populations introduced into Europe is not known.
Sources
Wiard, A.C.M.; van der Burgt (1999) Indication for establishment potential of Diabrotica virgifera virgifera LeConte in the Netherlands.
IWGO Newsletter, 19(1), 23-27.