Impact of the Asian wasp Dryocosmus kuriphilus (Yasumatsu) on cultivated chestnut: Yield loss and cultivar susceptibility

Dryocosmus kuriphilus is the most impactful alien pest of chestnut currently reported in almost the wholeEurope after its accidental introduction in Piemonte (North-west Italy) where it was found for the firsttime in 2002. The Piemonte Region Administration funded a project aimed to find control solutions basedon both the biological control of gall-wasp and the study of plant response. This work was carried out from2004 to 2013 and reports studies on assessment of production loss (2006–2012), cultivar susceptibility(2004–2013) and amount of nutrients subtraction caused by the insect (2012).The assessment of yield loss showed that infestation values (G/B = No. galls/bud) lower than 0.3 G/Bcaused no significant losses; values between 0.3–0.6 G/B originated a moderate decrease in productivity.A drastic decrease of productivity was observed for values above 0.6 G/B.A second objective was to assess varietal susceptibility in 62 cultivars. The susceptibility trait showeda wide range of variation from total resistance (7 cultivars: two Castanea sativa, one Castanea crenata and4 Euro-Japanese hybrids) to high susceptibility (>0.6 G/B; 14 cultivars).Finally, size and proximate differences in leaves with gall and healthy leaves were studied to assess thechanges due to infestation. Significant differences for leaf area, moisture, dry matter, ash, sugars, starch,and total carbohydrates were observed between the two types of leaves indicating a deep influence ofthe infestation on leaf functionality and on its photosynthetic capacity.