Page 11 - Volume 5, Issue 1, January 2012

© Benaki Phytopathological Institute
Integrated management of the red palm weevil 9
cluded. Although C. humilis and P. theophras-
ti show antixenotic and antibiotic mecha-
nisms of resistance, respectively, and larvae
of the weevil suffer higher mortality in these
host palms compared to P. canariensis, these
mechanisms are not enough to prevent in-
festation. Therefore, these species cannot
be considered as resistant against R. ferrug-
ineus .
Under Mediterranean climate, the pre-
imaginal development of R. ferrugineus in
P. canariensis takes 666.5 DD and the wee-
vil can complete 13 larval instars. Develop-
ment under these conditions is faster than
when fed on an artificial diet. Likewise, the
number of larval instars is also lower. Based
on the results obtained, less than one gen-
eration per year can be expected in areas
with a mean annual temperature (MAT) be-
low 15ºC and more than two in those with
MAT above 19ºC. Because a minimum of 2-3
generations are necessary for the weevil to
kill a P. canariensis palm, a minimum of two
years are necessary for a new infestation to
result lethal for a Canary Island date palm in
most of the northern shore of the Mediter-
ranean basin but shorter times would be ex-
pected in areas with higher MAT.
Oviposition in R. ferrugineus is strongly
affected by temperature. The thresholds for
oviposition and egg hatching obtained are
very close to MAT registered in most of the
northern shore of the Mediterranean basin
and clearly below mean monthly tempera-
tures in winter in this area. Under these cir-
cumstances, no new infestations would be
expected during most of the winter. These
results should be taken into account when
planning some palmmanagement practices
such as pruning or pesticide treatments.
Both imidacloprid and S. carpocapsae
in a chitosan formulation are highly effec-
tive against R. ferrugineus in the field. Differ-
ent timings and product combinations were
studied, and high efficacies were obtained
in all cases. Steinernema carpocapsae was
applied on a monthly basis and therefore
resulted more expensive and time consum-
ing than the drench applications of imida-
cloprid. However, this invertebrate biologi-
cal control agent would be most suitable for
ornamental palms in public areas.
An indigenous strainof B. bassiana, found
naturally infecting pupae of R. ferrugineus,
resulted highly virulent against all develop-
mental stages of the weevil in the laborato-
ry. Additionally, adults of either sex inocu-
lated with the fungus efficiently transmitted
the disease to healthy adults of the opposite
sex. Furthermore, B. bassiana infection re-
sulted in reduced fecundity and egg hatch-
ing. Semi-field preventive treatments on P.
canariensis palms with this strain were high-
ly effective against R. ferrugineus and this re-
sult confirmed the potential of B. bassiana as
a biological control agent against this pest.
The UJI-IVIA group has received financial sup-
port from the Spanish Ministry of Science
and Innovation (MCINN projects TRT2006-
00016-C07-01 and AGL2008-05287-C04/AGR)
and the Valencian Department of Agriculture,
Fisheries and Food (CAPA, project IVIA-5611).
Ó. Dembilio was recipient of a predoctoral
grant from IVIA.
Literature Cited
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Abraham, V.A. and Kurian, C. 1973. Chelisochesmorris
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