© Benaki Phytopathological Institute
Dembilio & Jacas
8
can be infected both by direct treatment
and by horizontal transmission from infect-
ed insects or cadavers to untreated insects
or to subsequent developmental stages via
the new generation of spores (Lacey
et al
.,
1999; Quesada-Moraga
et al
., 2004). These
unique characters make EPFs especially im-
portant for the control of concealed insects
as
R. ferrugineus
. Different strains of
Metar-
hizium anisopliae
(Metschnikoff) Sokorin
(Ascomycota: Clavicipitaceae) and
Beauver-
ia bassiana
(Balsamo) Vuillemin (Ascomyco-
ta: Clavicipitaceae) have been found in asso-
ciation with the weevil. Some of these EPFs
strains were tested against
R. ferrugineus
(Gindin
et al
., 2006).
Metarhizium anisopli-
ae
proved more virulent than
B. bassiana
.
However, none of the strains tested was
originally obtained from diseased
R. ferrug-
ineus
specimens. More recently, in prelimi-
nary studies, Sewify
et al
. (2009) successfully
reduced the incidence of
R. ferrugineus
un-
der field conditions in Egypt using a native
strain of
B. bassiana
isolated from a
R. ferrug-
ineus
cadaver.
3.2.4.1. Entomopathogenic nematodes:
Steinernema carpocapsae
Although no entomopathogenic nema-
tode has beennaturally recorded infecting
R.
ferrugineus
,
Steinernema carpocapsae
(Weis-
er) (Nematoda: Steinernematidae) proved
effective against
R. ferrugineus
in semi-field
trials including both preventive and curative
assays (Llácer
et al
., 2009). In a curative assay,
efficacies around 80 % were obtained, and
up to 98 % in a preventative treatment on
P.
canariensis
(Llácer
et al
., 2009). We have also
proved the high efficacy of this treatment
in
P. theophrasti
(Dembilio
et al
., 2011b). Un-
der field conditions, treatments using im-
idacloprid and
S. carpocapsae
, either alone
or in combination were not significantly dif-
ferent from each other, with efficacies rang-
ing from 73 to 95 % (Dembilio
et al
., 2010a).
Tapia
et al
. (2011) reached similar conclu-
sions in field trials in Southern Spain. There-
fore, EPNs should not be forgotten when de-
veloping strategies for treatments against
R.
ferrugineus
.
3.2.4.1. Entomopathogenic fungi:
Beauveria bassiana
In 2007,
R. ferrugineus
pupae presumed
to be infected with EPFs were collected in
a date palm grove in Spain (Dembilio
et al
.,
2010b). The
B. bassiana
strain isolated from
these pupae proved to infect eggs, larvae
and adults of
R. ferrugineus
. Furthermore,
B. bassiana
infection reduced adult lifespan
from one half to almost one tenth. Adults of
either sex inoculated with the fungus effi-
ciently transmitted the disease to untreat-
ed adults of the opposite sex conferring
rates of transmission between 55 and 60 %.
In addition, treatment with this
B. bassiana
strain significantly reduced fecundity (up to
62.6 %) and egg hatching (32.8 %). Likewise,
30–35 % increase in larval mortality was ob-
served in larvae obtained from eggs from
fungus inoculated females or from untreat-
ed females coupled with inoculated males,
resulting in an overall 78% progeny reduc-
tion compared to an untreated control. This
strain was subsequently tested in semi-field
preventive assays on potted 5-year old
P.
canariensis
palms. Efficacies up to 85.7 %
were obtained, and these results are indic-
ative that contact infection of adults actual-
ly occurred and confirm the potential of this
strain as a biological control agent against
R. ferrugineus
. Consequently, adults should
be considered as the targets of any treat-
ment involving this entomopathogenic fun-
gus because are actually the only free-living
stage. Strategies aimed at attracting and in-
fecting adult weevils could prove the most
effective way to spread the disease, and this
is one of the works that our group is devel-
oping at this moment.
4. Conclusions
Washingtonia filifera
is the only palm spe-
cies included in our studies showing mech-
anisms of complete resistance against
R.
ferrugineus
. This resistance is based on the
production of an antibiotic exudate. Howev-
er, the existence of additional mechanisms
of resistance in this species cannot be ex-
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