© Benaki Phytopathological Institute
Pathogenicity of entomopathogenic fungi on sisal weevil
51
its with the red palm weevil and its devel-
opment is completed within its host plant,
adults are the only exposed stage to ento-
mopathogenic fungal treatments (Gindin
et al.,
2006; Dembilio
et al.,
2010b). There-
fore, the longer survival of an infected host
increases the possibility of interacting with
other individuals and probably of trans-
mitting the pathogen. In this sense, a low-
er spore concentration of
B.bassiana
might
be more advantageous in a field applica-
tion, especially because our study showed
that the mean mortality did not differ sig-
nificantly between the two concentrations.
However, other aspects of the application
of these entomopathogenic fungi are not
yet fully studied. For example, potential
horizontal transmission between adults or
from adults to larvae and vertical transmis-
sion from infected adults to their offspring
should be elucidated (Glare
et al.,
2002; Gin-
din
et al.
, 2006; Dembilio
et al.,
2010b). Fur-
thermore,
M.anisopliae
and
B. bassiana
have
been found to reduce the fecundity of
R. fer-
rugineus
(Gindin
et al.
, 2006; Dembilio
et al.,
2010b). If a similar effect can be proved on
S.
acupunctatus
, then even strains that caused
lower levels of mortality might be a useful
tool in the control of the weevil.
Another important finding of the pres-
ent study is the high mortality of larvae
caused by all the strains tested. In most
of the cases, mortality in the larval stage
reached 100%. Although our methodology
of immersing the larvae differs considerably
from the natural infection, such high mor-
tality levels in controlled conditions sup-
port these strains as candidate biological
control agents. While the larvae of the wee-
vil are the most destructive stage they are
also the most concealed life stage (Cami-
no Lavin
et al.,
2002; Lopez-Martinez
et al.
,
2011), challenging the application of the en-
tomopathogenic fungi. It is, however, pos-
sible that entomopathogenic fungal endo-
phytes are effective against larval stages of
the weevil. Among many others, the ento-
mopathogenic fungi
B. bassiana
,
M. anisopli-
ae
and
I. fumosorosea
have been reported as
endophytes of several plants (Gomez-Vid-
al
et al., 2006;
Quesada-Moraga
et al.
, 2006;
Vega, 2008) and attempts have been made
to introduce entomopathogens into host
plants for the control of pests (Gomez-Vid-
al
et al.,
2006, Posada
et al.,
2007; Valdes Es-
trada
et al.
, 2014). If the strains studied here
could be introduced into agave plants they
could possibly act as successful biocon-
trol agents due to their high pathogenicity
against larvae.
In conclusion, our results prove that the
strain IBB 010 of
B. bassiana
is highly patho-
genic to both adults and larvae of
S. acu-
punctatus
and could be considered as a
biological control agent of the weevil. Addi-
tionally, application of lower concentrations
of IBB 010 was shown to prolong the adults’
survival time, without reducing the mor-
tality levels. This should be taken into con-
sideration, as a positive effect for strategies
Table 1.
Mean survival time ± SE (days after treatment) for larvae and adults of
Scyphopho-
rus acupunctatus
treated with
Beauveria bassiana
,
Metarhizium anisopliae
and
Isaria fumoso-
rosea
spore suspensions.
Treatment
Concentration (spores/ml)
Mean survival time ± SE (days)
Larvae
Adults
B. bassiana
2.12 x 10
7
5.47±0.351
a
10.20±1.055
a
2.12 x 10
6
6.80±0.251
b
14.74±0.999
b
M. anisopliae
1.27 x 10
7
5.00±0.359
a
15.65±1.031
bc
1.27 x 10
6
5.67±0.308
ab
17.20±1.210
c
I. fumosorosea
7.45 x 10
6
4.73±0.314
a
17.50±1.025
c
* Mean survival times within columns followed by the same letter are not significantly different (LR test, α=0.05)
* Mortality was recorded for up to 11 and 21 days for larvae and adults, respectively
