Case study of a new method for the classification and analysis of Dryocosmus kuriphilus Yasumatsu damage to young chestnut sprouts.

Dryocosmus kuriphilus is a new chestnut pest that is causing a serious problem worldwide. This gall wasp causes severe infestations of Italian Castanea sativa stands, which lowers their productivity. The most effective method for controlling gall wasp infestations is to introduce the parasitoid, Torymus sinensis, although experience shows that it can be 6–18 years before it is effective in reducing the infestation to acceptable levels. From a silvicultural point of view, it is important to reduce the damage as rapidly as possible to maintain plant vigour and fruit production, thereby avoiding chestnut stand degradation and abandonment before biological control is effective. This study analyzed the damage caused by Dryocosmus kuriphilus during normal plant development and detected differences in plant susceptibility, irrespective of genetic factors. Data were collected from a young Castanea sativa coppice stand in Tuscany (Italy) where damage was evaluated during the 2010 growing season. The study consisted of two phases: 1) classification of the damages caused by galls; and 2) studying the galls and damage distribution effects on different vigour chestnut sprouts to determine whether there were preferred oviposition sites or different degrees of susceptibility to gall wasp attack depending on a plant's physiological state. The D. kuriphilus damage classification scale was based on two factors: damage position (the vegetative organ attacked) and damage effect (abnormal organ development caused by galls). This classification included damage types that had not been previously described in literature. The statistical analysis identified differences in damage susceptibility in terms of: axis (stem or branches), plant organs (shoots, leaves, or buds), position of the attacked node (high or low region of the axis), and sprout vigour. Information on the D. kuriphilus damage distribution and its effect on plants with different levels vigour can be used to develop suitable cultural practices that could reduce the negative impact of this insect on fruit and wood production.