Studio della simbiosi tra Aedes albopictus (Skuse) e Wolbachia pipientis in rapporto allo sviluppo di tecniche di lotta basate sulla incompatibilità citoplasmatica
Author(s)
Calvitti, Maurizio
Date Issued
March 7, 2008
Type
Doctoral Thesis
Abstract
Aedes albopictus (Skuse) (Asian Tiger Mosquito) is an invasive
desease vector, spreading in Europe with some countries heavily colonized
(Albania and Italy) and others in the process of colonization (e.g. Croatia, France,
Greece, Montenegro, Spain, Switzerland). The spread of Aedes albopictus (Skuse)
is continuing also in Africa and America continents.
Recently an epidemic of Chikungunya virus, supported by Ae. albopictus,
took place in Northern Italy with more than 200 human cases.
The control of this species with conventional methods appears particularly
difficult mainly due to the large amount of breeding sites available in private areas.
The experience conducted until now on community participation showed
unsatisfactory results and consequently Ae. albopictus gained the role of main
mosquito pest in most of the urban areas of the peninsula.
Because of its recent introduction, the urban-related distribution, the low
active dispersal potential, this species has been considered a suitable target for
Sterile Insect Technique application, a suppression strategy that employs releases
of sterile males.
Previous studies have demonstrated that cytoplasmic incompatibility (CI), a
form of sterility induced by the intracellular bacterium Wolbachia, can be used,
instead of insect radiosterilization, as a mean for suppression strategies against
target species with appropriate patterns of infection (coexistence of infected and
uninfected populations, presence of populations harbourig different strains of
Wolbachia). Application of this approach to a wider range of target species has
been restricted by the lack of favourable patterns of infection as occurs in Ae.
Albopictus reported to be uniformly infected with two Wolbachia strains.
More recently, significant advances in microinjection methodology made it
possible to transfer Wolbachia infection over genus barrier into not naturally
infected hosts. Transinfection experiments based on the use of infected cytoplasm
from early embryos resulted in the establishment of isofemale lines carrying a new
Wolbachia infection in Aedes aegypti and Ceratitis capitata expressing complete
CI. In this way, the potential role of Wolbachia induced CI in pest control resulted
increased.
In this work we studied the symbiosis between Ae. albopictus and
Wolbachia in order to ascertain the role of Wolbachia-induced CI as a potential
tool for Ae. albopictus genetic control.
In the first part of the work, we investigated the pattern of distribution of
Wolbachia in Ae. albopictus and the effects of infection on adult fitness.
Furthermore we characterized some key parameters of the symbiosis such fidelity
of maternal transmission and CI level. In the second part of the work, our main
purpose was to generate a new incompatible infection in Ae. albopictus for genetic
control.
From the analysis of the pattern of distribution of Wolbachia, we found that
Ae. albopictus is uniformly superinfected with two Wolbachia types (wAlb A and
wAlb B). This means that it is not possible to identify natural incompatible strains
in this mosquito species and that artificially generated incompatible infection is
required.
Results from the study of the effects caused by the infection on adult fitness
allowed to associate an increase in survival capacity of females with the presence
of Wolbachia. Differently from data reported in literature, we found that the effect
of symbiosis on fertility and fecundity was not statistically significant.
By comparing infected and uninfected males we ascertained that Wolbachia
infection did not affect male longevity, mating competitiveness and sperm
capacity.
Results from the study of maternal transmission of infection and CI
confirmed previous data reported in literature. Maternal transmission efficiency
and CI were found at 100%. We confirmed that the multiple Wolbachia infections
which naturally occur in Ae. albopictus make this mosquito a useful system in
which to study the potential application of CI in insect pest control.
In the second part of the work, we developed a methodology to accomplish
the transfer of Wolbachia, via embryonic microinjection. We have evaluated the
supportive host background, the adaptation and the induction of CI, when
transferring in Ae. albopictus new Wolbachia strains from other infected species
(wMel from Drosophila melanogaster and wPip from Culex pipiens). We found
that Ae. albopictus can be artificially infected with both wMel and wPip strains. In
particular, transfected wPip males resulted incompatible when crossed with
uninfected females (egg mortality nearly 100%). Because transfected females were
not able to survive enough for reproduction, it was not possible to establish
transfected lines. Although these results are preliminar, they provide relevant
information on the possibility to obtain transfected lines of Ae. albopictus showing
a higher CI level than observed in transfected lines produced until now.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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