© Benaki Phytopathological Institute
Gkounti
et al
.
50
The mean survival time of the treat-
ed larvae differed significantly at different
fungi species and different concentrations,
namely the low concentration of
B. bassi-
ana
(6.80±0.251 days) compared to the oth-
er treatments (4.73-5.67 days) (
X
2
=8.3,
df
=4,
P
=0.0807; Table 1).
The mean survival time differed signifi-
cantly for adult weevils that received differ-
ent treatments (
X
2
=17.5,
df
=4,
P
=0.0016; Ta-
ble 1). Adult weevils treated with the high
concentration of
B. bassiana
exhibited the
shortest survival time (10.20±1.055 days)
(Table 1). Overall, the survival time of larvae
was significantly shorter than that of adults
(
X
2
=105,
df
=1,
P
<0.001).
Discussion
All species of fungi proved to be highly ef-
fective on larvae of
S. acupunctatus
. Fur-
ther wider dose range tests would be neces-
sary to show the dose effect, the differences
among strains and the potential of the test-
ed strains in lower concentrations. Howev-
er, our results showed that the examined
strains of entomopathogenic fungi are able
to infect larvae and adults of the sisal wee-
vil. Although all strains managed to fully
complete their life cycle by sporulating on
S. acupunctatus
cadavers,
B. bassiana
proved
to be the most pathogenetic to adult wee-
vils. Several studies have pointed out the re-
lation between strains of entomopathogens
isolated from specific hosts and the high vir-
ulence towards the host genera (Fargues
and Robert, 1983; Maurer
et al.,
1997). There-
fore, the high virulence of the strain IBB010
of
B. bassiana
might be related to its source
of isolation, an infected red palm weevil ca-
daver, as both the red palm weevil and the
sisal weevil belong to the same tribe of
Rhynchophorini.
Until now,
B. bassiana
is the only ento-
mopathogenic fungus species mentioned
as a natural enemy of the weevil in its place
of origin (Aquino Bolanos
et al.,
2011). Our re-
sults showed that the concentration of 2.12
x 10
7
spore suspension of
B. bassiana
caused
a quicker death of adults compared to spore
suspensions of
M. anisopliae
and
I. fumoso-
rosea
. Moreover, a 10-fold increase of the
diluted spore suspension of the
B. bassiana
strain from 2.12 x 10
6
to 2.12 x 10
7
decreased
the mean survival time for adults by almost
4 days .
The sisal weevil has identical life hab-
Figure 2.
Development of external fungal mycelium on cadavers of
Scyphophorus acupunctatus
adults:
Beauveria bassiana
(a),
Metarhizium anisopliae
(b) and
Isaria fumosorosea
(c).
(a) (b) (c)
