Climate as a possible driver of gall morphology in the chestnut pest Dryocosmus kuriphilus across Spanish invaded areas

The alien cynipid waspDryocosmus kuriphilusYasumatsu, 1951 is a serious pest of chestnuts(Castaneaspp.) in Japan, North America and Europe, causing fruit losses while inducing gallsin buds. WhileD. kuriphilusgalls have a recognizable and roughly invariable globular shape,their size varies, reaching up to 4 cm in diameter. Among other factors, such variation maydepend on different climatic conditions in different attacked areas. Here, we sampled andmeasured 375D. kuriphilusgalls from 25 localities throughout the Iberian Peninsula, includ-ing both cold and rainy northern (Eurosiberian) areas and warm and dry central-southern(Mediterranean) areas, to test the effects of climate and geographical location on gall morph-ology. The analyses indicate that gall mass and volume follow a pattern that can be associatedwith a climatic cline. In particular, the Eurosiberian galls were smaller than the Mediterraneangalls according to differences in climatic conditions. In the southern areas, the greaterinsolation regime does not allow the chestnut trees to be distributed at lower altitudes, butthe high rainfall and humidity regime of the mountain enclaves allow their presence. Theseconditions of insolation and precipitation seem to influence the morphological characteristicsof the galls ofD. kuriphilus.This study was financed by an Encomienda de Gestión from MAPAMA to Agencia Estatal CSIC, 16MNES003, awarded to JLNA,DGT, JF Gómez and CP, and by project AGL2016-76262-R (AEI/FEDER,UE), awarded to JLNA.Peer reviewe