Today we are going to talk about a type of pest that directly affects the chestnut tree. It’s about the chestnut wasp. Its scientific name is Dryocosmus kuriphilus. It is a cinipede insect that comes from China and was first detected in Spain in 2012. Over time, it has spread to practically the entire Spanish area. It is a very dangerous type of pest for these trees.
In this article we are going to tell you about all the characteristics, life cycle and treatment of the chestnut wasp.
Key features
It is a type of insect whose adults make their flight in the spring time. It is at this time that they lay their eggs in the yolks of the leaf axils. Adults are parthenogenic females. This means that they do not need to be fertilized to be able to lay eggs. Each of them it is capable of laying up to 150 eggs. This ability of the females makes the plant have a very rapid expansion.
Among the characteristics that the young have is that they remain in the form of larvae until the budding time in the following year. It is here that the sap begins to rise and the buds of the branches begin to sprout. This is when the larvae come out of dormancy in order to feed on the tree’s nutritional reserves. The problem with this type of feeding is that they cause a kind of galls that cause the reduction of the leaf surface that can photosynthesize by up to half. This problem to attack the chestnut tree does not allow it to carry out photosynthesis well.
Biological fight against the chestnut wasp
As we have seen, it is a type of pest that is quite difficult to control. This means that various remedies have to be devised. So far, the only effective fight is the biological one by releasing another species of parasitoid insect. It’s about the insect Torymus sinensis. The way to control it comes because it puts its eggs in the gills and they feed on the larvae of the chestnut wasp. This solution involves the realization of massive releases of adults in the budding season. More or less between 6 and 8 years of performance are required for those cases of too much infection to be able to reach a balance of the populations.
This is to be expected since it is an all-natural biological control outside of artificial pesticides. By the time the populations of both insects reach equilibrium, the release of new individuals is no longer necessary. The effects of the pest cease to act by affecting production. An example of these population controls has been in Galicia. Experimental releases of this parasitoid insect began in 2015. Despite this, the starting point is considered the year 2018, since it was the year in which they began to carry out mass releases.
Recently in Spain the release of various producers has been approved, with up to 4 companies in Spain that are authorized for the commercialization of parasitoid insects. Therefore, by being able to commercialize it, it means that releases can be made at a particular level.
Release results
Good data can be obtained from the release results. Releases have been taken into account and a series of field surveys have been carried out. They were collected andbetween 5 and 10 gills of 4.400 points and Torymus was recovered in 53 of them. Here 146 individuals were found. This shows that the release of the parasitoid insects is from the chestnut wasp has a success rate of 3% in the first year. It was the first year of the mass release, which is quite a hopeful result. An exponential growth of this parasitoid insect is expected in the coming years that help better to control populations of the chestnut wasp.
Practically almost the entire territory of the Iberian Peninsula has chestnut producing areas. In these areas there are affected chestnut trees and releases of this parasitoid are being carried out in most of all the mentioned regions.
Varieties resistant to chestnut wasp
Let’s see what are the different species and varieties resistant to the chestnut wasp. Among the former we find some very tolerant varieties such as Negral, a longuistaminated variety, widely used as a pollinator, or Longal, one of the most demanded varieties for the processing industry. Out of the less tolerant we find the De Parede or Ventura varieties among others. None of these traditional varieties have managed to show total resistance to the pest.
Therefore, some action guidelines have been established against this pest. Let’s see what the main action points are:
- You don’t have to remove the guts. It is possible that the galls created by the chestnut wasp may already be living within the parasitoid. Therefore, we could be harming this type of biological fight. We must bear in mind that the Torymus remains in the dried gills until its emergence the following spring. It is also important to note that they should not be removed during winter pruning. In any case, the pruned branches can be left in the plot so that the parasitoid larvae can survive.
- The use of insecticides is not advisable. It has already been concluded that insecticides have no effect against the pest. In addition, they could affect the parasitoid.
- Water and fertilize during the summer time it is a good option to achieve post-flight growths of the chestnut wasp. In these buds they can sprout free of the pest the following year thanks to these practices.
- In the case of clearing, it is advisable not to do them in the spring time. This is because Torymus feed on pollen and nectar and can use all vegetation as shelter. If we want the parasitoid to be able to develop in good conditions and combat this pest, it is better to avoid clearing in the spring time.
I hope that with this information you can learn more about the chestnut wasp and how to combat it.
