Spread of the oak processionary caterpillar in the Province of Antwerp
To gain an overview of the spread of the processionary caterpillar in the Province of Antwerp, each local authority in the province receives a brief questionnaire each year. By this means data are collected on the number of infested locations, the number and size of nests, control methods and varieties of tree.
Current oak processionary caterpillar situation – 2008
Of the 70 local authorities, 57 responded to the annual survey. Every local authority received reports of problems related to oak processionary caterpillars.
Map 1 shows the estimated number of locations infested with caterpillars. The reports only relate to locations in built-up areas or in public places, where caterpillars can cause problems to the population. The map shows that there were many local authorities in the Province of Antwerp with large numbers of caterpillars. Eleven local authorities, distributed over the province, had low numbers of caterpillars. Eight local authorities carried out preventive spraying in built-up areas and public places.
Map 2 shows the changes relative to 2007. In 2008 there were fewer local authorities where the number of reported locations increased (14 compared to 59 in 2007). Thirteen local authorities (four in 2007) had a relatively low number. The situation remained unchanged in 30 local authorities.
Map 3 – the problem map – shows the size of the problem experienced by residents based on a level distribution and reflects the burden on the agencies actively involved in pest control.We can deduce the following from the data collected:
Most of the local authorities are faced with a large problem.
Previously major problems were confined to the north of Antwerp. Now we see that major problems are distributed over the entire province.
Every local authority received reports. Processing of data for Level 2 (the local authority encounters oak processionary caterpillars for the first time) was discontinued for the Province of Antwerp in 2001.
Key to maps
Level graduation based on the burden on the agencies actively involved in control and the trouble experienced by residents:
Level zero: no precise data known.
Level one: there are hardly any locations in which caterpillars occur (< ten) so that residents experience few problems and control measures do not affect the workload of the relevant agencies (< two days' work).
Level two: the local authority encounters oak processionary caterpillars for the first time.
Level three: there are few or a moderate number of locations in which caterpillars occur (> ten and < twenty) so that residents experience problems and control measures affect the workload of the relevant agencies (up to one week's work).
Level four: there are a moderate number or many locations (> twenty) in which caterpillars occur so that residents experience major problems and control measures have a significant effect on the workload of the relevant agencies (more than one week's work).
Monitoring of the oak processionary caterpillar since 1995
Monitoring and the provision of information and advice on the oak processionary caterpillar by the Provincial Institute for Hygiene (PIH) to the local authorities in the Province of Antwerp has now taken place for fourteen years.
Since 1999, the province has surveyed the local authorities each year by means of a standard questionnaire. It gauges the number of reported locations infested with oak processionary caterpillars and extent of the problem.
We compare thedata for the period of 1999 to 2008 to see whether there is a trend.The results give a general idea of the situation. The data is affected by preventive actions and the provision of advice.
The problem map (based on subjective observations and numerical data) shows a clear trend since 1999. If the data for 1995 and 1996 is also translated into problem maps, the trend is even more evident. Several information and control programmes were conducted in 1997 and 1998, but there is no data available that can be translated into problem maps.
The graph below shows a slight increase in the problem in 2004 and 2005. The problem decreased in 2006, but then increased suddenly in 2007 and 2008. The severity of the problem was greater than in 1997.
Title of the grap: Number of local authorities with highest level of problems (levels 3 and 4 on Map 3)
The X-axis: Number of local authorities
The Y-axis: Year of recording and survey
In general, we can state that until 2003 the problem (high number of infested locations) was confined to the north of the North Campine and Antwerp region. In 2004 and 2005, the problem spread to South Campine and the Mechelen region. In 2006, the problem was confined to the Mechelen region; in 2007 it spread to South Campine, Antwerp, and part of the north. In 2008, the problem extended over the entire province.