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Piégeage de détection des foyers de chrysomèles des racines de maïs, (Diabrotica virgifera virgifera Lecomte )

Detection trapping for western corn rootworm (Diabrotica virgifera virgifera Lecomte )

Context

The western corn rootworm, Diabrotica virgifera virgifera Lecomte, is an important pest of corn in North America. It has been introduced by accident in Serbia in the early nineties, from where the infestation has spread in the old Yugoslavia and in Hungary. Today, this very big infestation focus has reached Bulgaria, Romania, Ukraine, Slovakia and Austria.

This insect doesn’t move itself on long distances. However, it can be transported by several land vehicles or by planes, and two important focuses have been discovered in Italy. Little focuses have also been discovered in Switzerland, in several locations in France, in England and in the Netherlands. A remarkable constancy: all the focuses have been discovered near international airports.

On the request of the Federal Agency for Safety of the Food Chain (AFSCA), The CRA-W is involved in the deployment of a pheromone trap network targeting to detect beginning focuses.

Objectives

The aim is to attempt to detect any western corn rootworm introduction that could have given rise to focus development.

Description of tasks

Monitoring and emergency plan definition

During the spring of 2003, with the collaboration of CIPF, CLO and CRA W, the AFSCA was built up a trapping campaign programme for detection of western corn rootworm. An emergency plan was also prepared in case insects would been discovered on the Belgian territory.

Expected results

Trapping campaigns in 2003 and 2004

At the beginning of July, 353 « PAL » traps were disposed in area considered as most probable entry ways for the insect: proximity of airports, motorway parking places, industrial parks, etc. These sites were classed into three groups of susceptibility: “very critical”, “critical” and “susceptible”. In each of these sites, respectively 30, 15 or 5 traps were disposed.

The program included the deployment of pheromone traps in the border of cornfields (2 to 4 traps distant of 100 m between them per field). A survey was made two times a month since the 10th of July to the 10th of October.

Until the end of August, None insect had been caught. However, since the 3rd of September to the 3rd of October, 69 western corn rootworm were caught in 17 fields distributed in three focuses located within a radius of 5 km around the International Brussels airport. Probably the introduction of the first insects in this area had occurred one or two years earlier. D. virgifera has been detected nowhere else in the country.

In 2004, a similar detection program was renewed. 400 traps were disposed on the 1st of July, by preference in cornfields where corn was also the previous crop. In September and October, seven individuals had been caught in traps located next to the infested field of previous year.

Focuses management

Within a radius of 1 km around each infested field, a “focus zone” was delimited. In this area, all cornfields were sprayed with pyrethroïds (two treatments with a 2 weeks interval).
In addition, some other precautions has been taken in the focus zones:

 No corn plant or part of corn plant could be transported out of the zone before the end of insect flights (1st of October).
 No soil could be transported out of the cornfield of the zone.
 Equipment used in cornfields or in contiguous fields didn’t may leave the zone without complete washing to avoid transport of infested earth.
 Corn cropping is forbidden in 2004 and 2005 in the cornfields of 2003; In the other fields of the focus zone, corn cropping was permitted, but it had to be treated with an insecticide during July.
 Compulsory destruction of corn regrowth.

In the “safety zones” (ring of 1 to 6 km around each source), the follow-up of traps was re-enforced. No restriction for growing corn was taken in 2004 nor 2005, on the condition of treating corn following corn. An active information for farmers was also organized.

Results obtained

New perspectives for trapping ?

The possibilities for a larva of D. virgifera to reach the adult stage in the absence of corn are quite vague. It seems that the phenomenon is biologically possible, but rare in real conditions, as few grasses have a sufficiently important root system to provide the larvae with a sufficient feeding phase.

Also, formal information is lacking about the possibility for a D. virgifera egg to pass two successive winters in diapause. Finally, one does not know if egg-laying of D. virgifera are possible out of corn crops and what distance from a corn crop. It is thus not certain that crop rotation is a sufficient obstacle to the development of sources of D. virgifera.

For this reason, CIPF and CRA-W had the idea of establishing, in spring 2004, trap fields in the focus zones marked out in 2003. These fields would have been of very small dimensions (thus easy to spray), made up of several varieties with different stages of precocity and spread out in the focus zones at the rate about 10 per zone. Pheromone traps would have been set up in each and checked regularly. The aim of this project was to try to draw towards these attractive fields (fresh silks produced by plants of delayed-maturity, plants still green at the end of deason in a zone where grain corn is dominant, …) the D. virgifera wich might have reached adult stage in the absence of corn, rather than let them wander in an uncontrolled fashion. This idea didn’t take shape in 2004, but will maybe be achieved in the future.

Partners

AFSCA (federal agency for food chain safety).
CIPF (independant centre for forage promotion).
CLO (flemish agricultural research centre).
CRA-W (Walloon agricultural research center).

Funding

  • FASFC - Federal Agency for the Security of the Food Chain
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