Dipartimento di Biologia e
Biotecnologie Charles Darwin

The Red Palm Weevil (RPW), Rhynchophorus ferrugineus, Olivier (Curculionoidea,
Dryophthoridae), is an invasive pest species from southeastern Asia and Melanesia. Since the '80,
the phytophagous colonized through the Middle East almost all the countries of the Mediterranean
Basin, including Italy. Unfortunately, actual actions of integrated pest management revealed to be
inadequate and the stem-boring larva of this pest is causing huge damages to several palm species
of the family Arecaeae. Many of those palms are economically important for agricultural and
ornamental purpose. Therefore, a great attention has been recently focused in studying this species
for finding sustainable and effective eradication strategies, like biological control ones.
Connecting the RPW rapid spread with its high reproductive success, the aim of this study was to
shed light on particular aspects of its mating system, such as the presence of polyandry and postcopula
sexual selection mechanisms. For this purpose, we developed 16 polymorphic microsatellite
loci, 14 of them de novo isolated through an innovative approach based on 454 Next Generation
Sequencing and bioinformatics mining (and 2 additional ones picked from literature). We then
evaluated their reliability for paternity determination in laboratory cross experiments and we also
discussed their use for more in depth mating system studies through simulations and power
analyses. In order to maximize the probability of exposing females to males carrying different
alleles, thus improving the resolution power of our system, we also performed a preliminary
analysis of genetic variability on natural populations of RPW from its primary and secondary
distribution areas. Our aim was in fact to identify well differentiated source populations for the
collection of the individuals to be crossed. To investigate whether the female behavior of multiple
mating really produces progeny from different males, we conducted two laboratory experiments
crossing a single virgin female to two males carrying different genotypes at selected loci. We then
reared and genetically characterized the filial generation in order to assess the paternity of progeny
from comparison with potential parental genotypes.
Our results suggest that, even if multiple mating occurs frequently, it is the last male that almost
exclusively contributes to the progeny (P2-value=99.2%). This is probably due to a kind of postcopulatory
sexual selection mechanism based on last male sperm precedence, like some evidences
from mating experiments with sterilized and fertile males also suggest. Such a phenomenon,
widespread in many insect orders, could be produced by sperm competition between males or even
by female cryptic choice. Certainly, our findings require more in depth studies on these aspects of
the mating system of RPW, and should be carefully considered in the planning of biological control
programs against the pest, such as Sterile Insect Technique.