Page 4 - Volume 5, Issue 1, January 2012

© Benaki Phytopathological Institute
Dembilio & Jacas 2
ranean Basin in 1993, R. ferrugineus spread
very quickly after 2004, when it was found
for the first time in the Region of Valencia
(eastern Spain) (Tejedo, 2006). At that time,
the Universitat JaumeI-Institut Valencià d’In-
vestigacions Agràries (UJI-IVIA) Unit started
a research line aimed at the management of
this weevil.
Henceforth we will present a summary
of what was already known about the bio-
ecology and the management of this pest
combined with the new findings that our
group achieved.
2. Bio-ecology of R. ferrugineus
2.1. Life cycle
Female R. ferrugineus weevils lay their
eggs singly at the base of the palm fronds in
separate holes made with their rostrum. Ne-
onate larvae bore into the palm core making
tunnels and feeding on its inner contents.
As larvae molt, their appetite increases and
they tend to feed primarily on the soft tis-
sues surrounding the apical meristem. Ma-
ture grubs migrate to the periphery of the
stem and prepare a cocoon made of palm fi-
bers. After covering themselves with the co-
coon, larvae enter a prepupal stage and then
a pupal stage (Murphy and Briscoe, 1999). A
new generation emerges and these adults
may remain within the same host and repro-
duce until the palm meristem is destroyed
resulting in the palm death. Subsequently,
adults will fly away and look for new hosts.
2.1.1. Life cycle in Phoenix canariensis
The Canary Islands Date Palm, Phoe-
nix canariensis hort. ex Chabaudis R. fer-
rugineus most susceptible host and its pre-
ferred host in the northern Mediterranean
Basin. Although the life cycle of R. ferrug-
ineus had been studied by some authors in
different countries, on either artificial sub-
strates or plant portions under controlled
environmental conditions (Table 1), no re-
sults on the life cycle of R. ferrugineus in any
of its hosts under natural conditions were
available. Therefore, we decided to deter-
mine the thermal constant and the number
of larval instars of R. ferrugineus when feed-
ing in live P. canariensis palms under natu-
ral conditions in a Mediterranean climate
(Dembilio and Jacas, 2011a). Based on mea-
surements of the head capsule width, the
existence of 13 larval instars in R. ferrugineus
was established. Our results demonstrated
that R. ferrugineus requires 40.4 DD for egg
hatching under laboratory conditions, 666.5
DD for complete larval development in P.
canariensis and another 282.5 DD to reach
adulthood. Therefore, depending on mean
temperatures, larval development can be
completed in about 40 days in summer and
up to 160 days in winter-spring. Likewise, pu-
pae can complete their development in 13
days in summer but need several months to
complete this stage from autumn to spring.
Based on these results and on the tempera-
tures in different climatic stations in the Ibe-
rian Peninsula, the mean number of gener-
ations of R. ferrugineus was estimated in the
respective regions. These results indicated
that less than one generation per year can
be expected in areas with mean annual tem-
perature (MAT) below 15ºC and more than
two where MAT is above 19ºC (Dembilio and
Jacas, 2011a). This is an important finding
because we have observed that a minimum
of two to three complete generations are
necessary to kill an adult P. canariensis, and
this means that at least two years would be
necessary for R. ferrugineus to kill a palm in
most of the Iberian Peninsula but more than
these would be necessary in northern Spain
and therefore a quarantine period of two
years as it is nowadays required by EU laws
(EU, 2007) could be insufficient to detect in-
fested palms in that area. Should these re-
sults apply to other regions, a complete plus
a partial generation per year would occur in
most of the Northern shore of the Mediter-
ranean Basin, whereas at least two complete
generations per year would be expected in
the Southern shore.
2.1.2. Lower temperature threshold for
oviposition
Temperature is the main abiotic factor