Local-scale dispersal patterns and susceptibility to Dryocosmus kuriphilus in different Castanea species and hybrid clones: insights from a field trial

Abstract

The chestnut gall wasp Dryocosmus kuriphilus is a major insect pest affecting chestnut trees worldwide. Medium and long-term control of this pest can be improved by using resistant or less susceptible cultivars and hybrid clones. In addition, little is known about the local patterns of dispersal of the pest. We obtained data from trees of 3 chestnut species and 27 hybrid clones in a field trial in NW Spain with the aim of evaluating the susceptibility of the material to the gall wasp and identifying possible drivers of local spatial dispersal. In the first 3 years of the invasion by D. kuriphilus, the number of trees attacked and the number of galls on each tree were spatially clustered. Tree height significantly predicted both variables, suggesting that gall wasps may use visual cues to locate suitable host trees, at least in the early stage of invasion. Assessment of the susceptibility of hybrid clones/pure species must take concurrent indicators of infestation levels into account. We suggest the use of indices involving galls on shoots because these enable good assessment of the damage to chestnut trees. The study findings add to existing knowledge on the susceptibility of hybrid chestnut clones. We report, for the first time, two hybrid clones resistant to the pest and one hybrid clone which exhibited consistently low values for all of the indicators of infestation level. The results have important implications regarding selection of plant material for use in afforestation in Spain, where the current high rate of chestnut planting is expected to continue.

Defensive patterns of chestnut genotypes (Castanea spp.) against the gall wasp, Dryocosmus kuriphilus

“…(UTM Coordinates: 587161 m E, 4786989 m N; ETRS89 H29T). The trial was established in spring 2004 to test certain traits of interest in the Galician breeding program for hybrid chestnut clones (Castedo-Dorado et al, 2021). Dryocosmus kuriphilus colonized the planting in 2015, which coincides with the beginning of our study.…”

“…We selected the four shady replicates for this study, to minimize variation due to topography and geographic orientation (Figure 1). The different genotypes showed high variability in susceptibility to D. kuriphilus, with seven clones showing total resistance after 4 years of attack (i.e., no galls in the crown in mid-summer) while others showed medium or high attack levels (see Castedo-Dorado et al, 2021). However, when visiting the trial in spring to collect leaves for other studies, we observed that some of these resistant clones showed small galls in leaves that, somehow, disappeared later (Figure 2).…”

“…Galls were counted in July of 2016-2018 by the same observers (ML and FC-D), using binoculars as needed. For this study, we only considered attacks in 2018, by which time D. kuriphilus was fully distributed across the area of the trial (Castedo-Dorado et al, 2021).…”

“…This hybrid material is being used in clonal forestry for wood and nut production and as rootstocks for grafting with traditional varieties. These hybrid clones show high variation in susceptibility to D. kuriphilus (Míguez-Soto et al, 2018;Castedo-Dorado et al, 2021). Little is known about the defensive patterns of chestnuts against D. kuriphilus, but HR was previously reported for one chestnut hybrid (Dini et al, 2012) and in a chestnut cultivar ecotype (Nugnes et al, 2018).…”

“…In 2015, the wasp started to colonize a field trial established with hybrids of the European and Asian chestnut as well as the parental species. The different genotypes present in the trial showed great variability in terms of their susceptibility to D. kuriphilus (Castedo-Dorado et al, 2021).…”