Chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu): antennal morphology and natural control
Author(s)
Riga, Francesca
Date Issued
June 26, 2013
Type
Doctoral Thesis
Abstract
Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae) is a gall wasp recently
introduced in Italy and Europe; it is a key pest of Genus Castanea.
Its control by chemical or agronomical methods is very expensive and not very effective.
With this work we intend to contribute to the knowledge of this dangerous pest investigating
two different aspects of the cynipid D. kuriphilus that can give information in a future plant
protection strategy: from one side, the study of the sensory receptors of the antenna, and on the
other the composition of the community of parasitoids related to this gall maker in central Italy.
In the first part of the work was carried out the morpho-functional survey of the antennal
structures through the techniques of electron microscopy.
This study, also associated with future electrophysiological and behavioral analysis will
certainly allow to develop measures of control and monitoring of D. kuriphilus such as confusion
or attraction / repulsion toward plants (pheromones).
In the second part are carried out surveys to deepen knowledge on parasitoid communities
associated with D. kuriphilus, in order to value the potentiality of these natural enemies in
implementation of biological control techniques.
ANTENNAL MORPHOLOGY
We carried out observations of Dryocosmus kuriphilus antenna by a Scanning Electron
Microscope (SEM) and by a Transmission Electron Microscope (TEM).
This antenna is geniculate and is composed of 14 antennomeres, the first proximal is the scape,
the second is the pedicel and the last 12 compose the flagellum.
The antenna has five different types of sensory receptors:
- sensilla with a mechanosensory function (ST);
- sensilla suitable to perceive volatile chemical stimula, with an olfactory function (MPS and
CS);
- sensilla with a mechano-gustatory function (SCH);
- sensilla with a possible thermo-hygrosensitivity (SS).
NATURAL CONTROL
The purpose of the study was to evaluate in the presence of indigenous parasitoids of D.
kuriphilus and to verify the presence of parasitoids of galling cynipid on spontaneous plants.
The research was carried out in four locations: two in the province of Ascoli Piceno (San
Pietro and Montemonaco) and two in the province of Rimini (Uffogliano and Piedimonte).
In order to investigate the presence of native parasitoids of D. kuriphilus in each of the four
chestnut were harvested 1000 (2010) or 200 (2011) galls of fore mentioned gall wasp.
The emerged parasitoids were placed in absolute ethanol and stored at -20 ° C and, after an
initial division into morphotypes, some representative samples were determined by the working
group of Prof. Alma of Turin University.
It has also taken place a collection of galls on the natural vegetation adjacent to the study
sites, in order to verify the presence of indigenous parasitoids of gall makers.
Finally, in the survey sites was carried out the analysis of the border spontaneous vegetation
using the scale of cover-abundance / sociability of Blaun Blanquet and was assessed the rate of
infestation of D.kuriphilus, calculated as a percentage of the total infected buds on the gems in the
sprig of a year.
In this study, D. kuriphilus parasitoid overall emergence rate was of 0.5% in 2010 and of
25.76% in 2011 (37.70% in spring and 13.83% in summer).
2011 data are far above the italian average values found in bibliography, where the emergence
rate is always under or across 2-3% threshold.
In all sites T. flavipes (Walker, 1833) (Toryminae, Torymini) was the most abundant species
collected both in Spring and in Summer period, with an average parasitism rate of 75.75%.
This study has shown that in T. flavipes the sex ratio is greatly female-biased, sign of good
adaptation of this native species to the new exotic host.
Further studies are needed to value the use of T. flavipes in biological control projects against
D. kuriphilus.
Furthermore this work showed the presence in the study places of a new italian association:
Mesopolobus lichtensteini (Mayr, 1903) (Pteromalidae, Pteromalinae ).
With regard to the collection of galls from spontaneous vegetation, we obtained from oaks
some insects already known as related to D. kuriphilus: Torymus sp., T. flavipes, Ormyrus nitidulus
(Ormyridae). Moreover we obtained from Andricus caputmedusae the parasitoid Megastigmus
stigmatizans (Torymidae, Megastigminae), a parasitoid that has not emerged from the chestnut gall
wasp.
O. nitidulus has only recently been reported associated to D. kuriphilus in Italy (Quacchia et
al., 2012).
Due to this study can be hypothesized a relationship between the presence of oak trees and the
consistence of parasitoid community.
Concerning phytosociological analysis it has been highlighted a greater presence of oaks in the
site where it has been detected a greater concentration of parasitoid, that could be ascribed to the
shift of parasitoids from cynipidae gall makers of oaks to the chestnut gall wasp.
However, further studies are necessary to assess the amount of the cynipid fauna in our study
area.
Additional information
Dottorato di ricerca in Protezione delle piante
Subjects
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