Aim of study:
To analyze the susceptibility of
Eucalyptus
and hybrids species to
Leptocybe invasa
through field assays.
Area of study:
The north of the Argentine province of Misiones (Colonia Delicia).
Material and methods:
A total of 11
Eucalyptus
species and 2 hybrids were surveyed for damage and severity of
L. invasa
infestation. Six evaluations were made during an annual period.
Main results:
The susceptibility ranking to
L. invasa
from highest to lowest was
E. tereticornis > E. propinqua > E. dunni > E. camaldulensis > E. grandis > E. major > E. longistrata > E. grandis × E. camaldulensis
. However,
E. moluccana, E. urophylla × E. grandis
and
E. urophylla
were tolerant to L. invasa.
Research highlights:
This study suggests that in Misiones,
E. tereticornis
is the most sensible eucalyptus species to gall wasp attack, whereas other species and hybrids presented low damage levels or tolerance to
L. invasa
region.
Author's contributions:
Conceived and designed the experiments, and wrote the paper: ERE and MES. All authors performed the experiments, read and approved the final manuscript.
Citation
Eskiviski, E. R.; Schapovaloff, M. E.; Dummel, D. M.; Fernandez, M. M.; Aguirre, F. L. (2018). Short communication: Susceptibility of eucalyptus species and hybrids to the gall wasp
Leptocybe invasa
(Hymenoptera: Eulophidae) in northern Misiones, Argentina. Forest Systems, Volume 27, Issue 1, eSC01.
https://doi.org/10.5424/fs/2018271-11573
Competing interests:
The authors have declared that no competing interests exist.
Introduction
Eucalyptus
is the most widely planted exotic species in the tropics, and play important roles in reforestation and production of timber, pulp, potential bioenergy feedstock, and other forest products (
Wyle & Floyd, 1998
;
Rejmánek & Richardson, 2011
). In Argentina,
Eucalyptus
spp. plantations occupy about 261,000 ha, mainly in the northeast region (
MAGyP, 2015
).
The eucalyptus gall wasp,
Leptocybe invasa
Fisher & La Salle (Hymenoptera: Eulophidae), native from Australia, is a worldwide pest in
Eucalyptus
plantations.
L. invasa
has expanded to more than 29 countries in Asia, Europe, Africa and the Americas (
Mendel
et al.
, 2004
;
Zheng
et al.
, 2014
). This insect was first repor-ted in Argentina in 2009 (
Aquino
et al.
, 2011
). The fe-male
L. invasa
lays her eggs in plant tissues causing the formation of galls on the leaf midribs and petioles and on the stem of new shoots, eventually leading to leaf-curling and premature aging of the leaves. Eggs overloading might cause death of youngs shoots, while severe attacks lead to leaf fall, stunted growth and may seriously weaken the tree (
Mendel
et al.
, 2004
). Gall development occurs as response to a physiological di-sorder caused by a specific relationship between plant and insect. It is highly dependent on specific small cha-nges in morphological and phenological characteristics of the plant, which determines the degree of suscepti-bility and coevolution between plant and insect (
Stone & Schönrogge, 2003
;
Zheng
et al.
, 2014
).
Eucalyptus
species show different susceptibility to
L. invasa
attacks (
Mendel
et al.
, 2004
) with
Eucalyptus grandis
W. Hill,
Eucalyptus camaldulensis
Dehnh and
Eucalyptus tereticornis
Smith being the most susceptible ones (
Thu
et al.
, 2009
). However, the susceptibility can be strongly influenced by local environmental factors, and therefore further susceptibility tests are needed in locations where eucalyptus trees are cultivated. The ob-jective of the present study was to evaluate the suscep-tibility of different
Eucalyptus
species and hybrids to
L. invasa
planted in the field in Argentina.
Material and methods
This study was conducted from March to November 2014 in Colonia Delicia, Misiones, Argentina (26°10'16" S, 54°33'15"W). The clime is subtropical without dry se-asons.
Eucalyptus
seedlings, less than one year old, were planted in a field experiment without irrigation.
L. invasa
damages were evaluated in a 1.35 ha field plot, with a spa-cing between plants of 3.0 × 2.5 m (1,333 plants/ha). The evaluated species were
E. camaldulensis, E. grandis, E. major, E. propinqua, E. tereticornis, E. dunni, E. molucca-na, E. longirostrata, E. urophylla
and the hybrids
E. gran-dis × E. camaldulensis and E. urophylla × E. grandis
(Table 1), planted in October 2013.
Provenances of Eucalypts species selected for the field trial.
The experiment was designed as a complete rando-mized block, with 4 blocks and 5 replications. In each block, 11 experimental plots of each species with 5 plants were randomly stablished, and all trees in these plots were surveyed for damage and severity of
L. invasa
infestation. Six evaluations were made during 2014 between March and November, evaluating the damage index (DI) and average damage index (ADI). DI scored the proportion of leaves and twigs damaged per tree, as follows: 0, no damage; 1 < 25%; 2, 25-50%; 3, 51-75%; 4 >75% (
Thu
et al.
, 2009
). DI was calculated as the percentage of trees affected. ADI was calculated according to:
ADI= Σ
ni·vi
/
Ni
where
ni
is the number of trees infected at DI=
i
,
vi
the da-mage index at level
i
, and
Ni
is the number of trees assess-ed per species. Based on maximum ADI values, a damage severity level was defined (
Thu
et al.
, 2009
): nil (ADI = 0), low (ADI: 0-1.0), medium (ADI: 1.1-2.0), severe (ADI: 2.1-3.0) and very severe damage (ADI: 3.1-4.0).
Statistical analysis was performed using analysis of variance (ANOVA) after checking that normality and homoscedasticity were fulfilled, and means were compared with the Tukey test (
p
<0.05), using InfoStat statistical software V 2016 (
Di Rienzo
et al.
, 2016
).
Results and Discussion
Damage incidence by
L. invasa
significantly differed among the tree species (
df
=18,
F
=28.42,
p
<0.0001). The highest damage incidence was observed on
E. tereticornis
and the lowest in
E. urophylla, E. urophylla × E. grandis
and
E. moluccana. E. grandis × E. camaldulensis, E. lon-gistrata, E. major, E. grandis, E. camaldulensis, E. dunnii
and
E. propinqua
showed medium damage incidence (Table 2).
Damage incidence (DI) and average damage index (ADI) of Leptocybe invasa infestation on Eucalyptus species
and hybrids in the field.
Based on ADI, in the six evaluations between March and November 2014, the resistance of eucalyptus species differed widely.
E. urophylla
and the hybrid
E. urophylla × E. grandis
seemed tolerant to
L. invasa
and no galls were produced. Six species (
E. moluccana, E. longistrata, E. major, E. grandis, E. camaldulensis, E. dunnii
) and the hybrid
E. grandis × E. camaldulensis
showed low damage severity. Medium damage was ob-served in one species,
E. propinqua
and severe damage occurred in
E. tereticornis
(Table 2).
Differences in susceptibility to the gall-forming insects of eucalyptus tested may indicate that genetic factors are involved in both, attractiveness to
L. invasa
for oviposition and suitability for
L. invasa larval
development. Similarly, synchronization of gall-forming species with host plant phenology is behind many cases of susceptibility as consequence of coevolution between eucalyptus plants and
L. invasa
. These factors open the chance of coping with this pest through the development of resistant and productive genetic stock, better than through chemical means (
Dungey
et al.
, 2000
;
Guerreiro
et al.
, 2015
). In this context, the order of susceptibility to
L. invasa
in Misiones was
E. tereticornis > E. propinqua > E. dunni > E. camaldulensis > E. grandis > E. major > E. longistrata >E. grandis × E. camaldulensis
. Other studies have also showed susceptibility to
L. invasa
of these species (
Mendel
et al.
, 2004
;
Thu
et al.
, 2009
;
Javaregowda & Prabhu, 2010
;
Zhu
et al.
, 2012
). On the other hand,
E. moluccana, E. urophylla × E. grandis
and
E. urophylla
resulted tolerant to
L. invasa
, as previously shown by
Thu
et al.
(2009)
,
Nyeko
et al.
(2009)
and
Guerreiro
et al.
(2015)
.
This study suggests that in Misiones,
E. tereticornis
is the most sensible eucalyptus species to gall wasp attack, whereas other species and one hybrid of regional economic importance like
E. dunni, E. camaldulensis, E. grandis
and
E. grandis × E. camaldulensis
presented low damage levels. The hybrid
E. urophylla × E. gran-dis
showed tolerance to
L. invasa
. More studies are ne-cessary to determine the tolerance to
L. invasa
of dif-ferent eucalyptus species and hybrids cultivated in the northern Argentine region.
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