Thursday, 5 May 2016

Another pest from the Far East - Chestnut leaf gall wasps.

Dryocosmus kuriphilus

It looks almost like a Christmas decoration, doesn't it.  But those two shining berry-like structures are a pest from China.  They are galls created by a minute wasp with the jaw cracking Latin name written below the picture.  The wasp is classified in a group known as cynips. Such wasps are about two to three millimetres long and pitch black in colour but with bright orange legs.
 Image of the wasp  taken from the Forestry Commission site, 
and originally courtesy of Gyorgy Csoka, 
Hungary Forest Research Institute,
The tiny wasp does not reproduce via normal mating.  The females lay eggs in small batches amounting to about 100 eggs at the end of summer. This is without any mating i.e it is parthenogenesis. The eggs are placed just inside the developing winter buds.  The larvae develop slowly and induce the surrounding plant tissues to develop into protective galls. The following summer the adults emerge to infect new buds.
 Gleaning information from the internet one learns that its original home is China, from it spread by 1940 to Japan,  and then to Korea in 1974 and on to the United States. In 2002 it appeared for the first time in Europe. The species has been extensively recorded from Italy since 2005. In 2007 it reached the south of France.
At that time the infested trees were burned but the spread has not been stopped. It has reached England and again burning of trees was tried.  
The pest weakens the trees which must have a toll on both fruit and timber production.
The insect is clearly now widespread through France.
It looks as though it is here to stay.  Just as the Asian hornet is now established and also the Asian Box tree  caterpillar so this Oriental Chestnut Gall Wasp is here to stay.