Dryocosmus kuriphilus

Pérez-Otero, R., Crespo, D. & Mansilla, J. P., 2017, Dryocosmus kuriphilus Yasumatsu, 1951 (Hymenoptera: Cynipidae) in Galicia (NW Spain): pest dispersion, associated parasitoids and first biological control attempts., Arquivos Entomolóxicos 17, pp. 439-448 : 443-444

D. kuriphilus phenology and parasitoids

Phenological results are summarized in Fig. 2 . Eggs were found all year long excluding April and May (although in January, February, March, June, November and December egg presence was sporadic). Wintering eggs presence was punctual and eggs were considered non viable (actually some of them could be exuviae). Larvae presence is more time-concentrated as larval stage becomes higer. First-instar larvae were found the whole year excluding May, and adults flight on June, July and August.

Our results slightly differ from those obtained by BERNARDO et al. (2013) and JARA (2015), although we could just contrast similar phenological stages (notice in both different larvae notation). Main divergence was found in egg presence. Those researchers found a narrower egg presence period, albeit we have considered our recorded egg presence for half a year as punctual.

We have interpreted JARA’ s (2015) first larvae stage as L1 and second larvae stage as L2 and L3 following his pictures. Our first-instar larvae results match with those obtained by JARA (2015) although are quite dissimilar to those found by BERNARDO et al. (2013). Interestingly we have punctually detected L 2 larvae in November and December 2016, explained by particular Galician climatic conditions that year. Adults flight period was similar between all performed and considered research.

Different gall provenances (with different climatic conditions) could provide a feasible explanation for phenological differences. In addition Galician climatic conditions in 2016 were specially warm and dry and, as a consequence, L 1 larvae hatching could begin earlier.

Recorded parasitoids and abundances are shown in Table 1. A total number of 201 parasitoid individuals belonging to at least 9 species were present in approximately 16100 galls analyzed between 2014 and 2016. In 2014 the dominant species were Ormyrus pomaceus Geoffroy, 1785 , Mesopolobus mediterraneus Mayr, 1903 and Torymus flavipes Walker, 1833 . The first two species were present in higher numbers as well in 2015 whereas in 2016 Eupelmus urozonus Dalman, 1820 was the most abundant species. The situation depicted in the last two years is quite different from 2014 since species abundance is by far more distributed and there is not a clear dominance. Dominant parasitoids seem to be quite characteristic depending on the studied site, albeit T. flavipes is prevalent in previous European research (see Table 2).

All recorded parasitoids were previously found and associated to D. kuriphilus galls in previous works except Mesopolobus xanthocerus Thomson, 1878 , which is mainly found associated to Andricus spp. galls (see ASKEW et al., 2013 for a review). This is, to our knowledge, the first record of M. xanthocerus associated to D. kuriphilus galls. Parasitoid results are quite complex to interpret in bibliography (see Table 2 and references therein) because they are greatly variable with time. In the first place, parasitoid records vary according to sampling effort. However differences between 2014 and 2016 (a total number of 123 and 67 recovered parasitoids respectively)

cannot be explained by sampling issues. In addition it has been documented that adaptation process between new hosts and native parasitoids requires time and it is very complex (see as an example FRANCATI et al., 2015: they have not obtained a regular increment of parasitoid abundance, but erratic results through consecutive sampling campaigns). A constant rise in the number and diversity of parasitoids could be hypothesized but further research is needed to assess the ongoing host-

parasitoid adaptation process along the next years.

Figures

Fig. 2.- Monthly D. kuriphilus phenology (E: egg; L1: first-instar larvae; L2: intermediate instar larvae; L3: terminal-instar larvae; Pp: pre pupae stage; P: pupae stage; A: adult). *: punctual presence; +: sterile eggs. Sweet chestnut fruit phenology is given for orientation (§: fructification and burr development).