Page 7 - Volume 5, Issue 1, January 2012

© Benaki Phytopathological Institute
Integrated management of the red palm weevil 5
0.75 eggs during the first 2 days of exposure
to the lower temperature. Based on the re-
sults obtained at constant temperature re-
gimes, a lower temperature threshold of
15.45ºC was estimated for oviposition. Tak-
ing into account all results obtained, a slight-
ly lower value, 13.95ºC, was calculated for
egg hatching. When these values were com-
pared with mean monthly temperatures in
Valencia and other selected locations in the
Mediterranean Basin, windows for oviposi-
tion and egg hatching could be established
(Figure 1). In most of the northern shore of
the basin, the oviposition period (OP) ex-
tended from early April to mid-October ear-
ly November and the egg hatching period
(EHP) from mid-March to mid/late October.
However, these periods were much short-
er in the southern shore and although ovi-
position would stop during the coldest win-
ter months, egg hatching would continue
during the whole year in the southwestern
part of the Basin (i.e. Egypt) (Dembilio et
al. , 2011c). Based on these results, any man-
agement practice producing wounds (such
as pruning or the cutting of an inspection
window in the crown), should be best per-
formed in winter, when oviposition is nota-
bly reduced and immature mortality is high-
est (Dembilio and Jacas, 2011a). Importantly,
even during this season, all wounds should
be immediately protectedwith a treewound
seal and, if possible, with an insecticide (Fa-
leiro, 2006). For the same reason, the fre-
quency of preventative treatments against
the weevil could decrease during the win-
ter, thus reducing the non-target effects of
these pesticides.
2.2. Host range
Chamaerops humilis L. and Phoenix theo-
phrasti Greuter are the two European na-
tive palm species and their host status was
not clear. Barranco et al. (2000) considered
C. humilis as resistant to the attack of R. fer-
rugineus . Nevertheless, the European Union
included this species in the list of R. ferrug-
ineus -susceptible plants (EU, 2007). This list
also included the genus Washingtonia spp.
However, in assays carried out by our group
in 2007 (Llácer et al., 2012), Washingtonia filif-
era (Lindl.) Wendl could not be infested with
R. ferrugineus whereas W. robusta could. Dif-
ferent semi-field trials (Dembilio et al ., 2009)
demonstrated that W. filifera and C. humi-
lis could not be naturally infested by R. fer-
rugineus adult females. Antibiosis was the
main, and perhaps the only, mechanism op-
erating in W. filifera, as a gummy secretion
produced by the plant resulted in complete
mortality of R. ferrugineus young instars. An-
tixenosis was the major mechanism of resis-
tance in the case of C. humilis. The base of
the fronds of this palm is very fibrous and
therefore not appropriate for oviposition.
However, this antixenotic mechanism of re-
sistance could be by-passed by artificially
infesting the palm with neonate larvae de-
posited in holes made with a drill (Barran-
co et al., 2000) and the same phenomenon
was observed for P. theophrasti (Dembilio et
al., 2011b). Therefore, C. humilis and P. theo-
phrasti palms formerly harmed either nat-
urally (e.g. attacked by Paysandisia archon
(Burmeister), damaged by the wind, etc.)
or artificially (e.g. after trimming or prun-
ing) could be attacked by R. ferrugineus, and
this fact should be taken into account when
dealing with these palm species.
3. Management of the Red PalmWeevil
3.1. Detection
A serious problem associated with R. fer-
rugineus is the difficulty of detecting the ear-
ly stages of infestation (Nakash et al., 2000).
Because of the cryptic habits of R. ferrug-
ineus , it is very difficult to detect infestations
in their early stage. Unless palms are con-
tinuously thoroughly inspected, this pest is
generally detected only after the palm has
been severely damaged. Careful observa-
tion may expose the following signs which
are indicative of the presence of the pest:
dieback in the apical leaves in the canopy,
where broken or cut leaves (symptom of
larval damage to the meristem tissue) be-
come visible, holes in the crown or trunk
from which chewed-up fibers are ejected