of forest insects' parasitoids
researches currently focus on two main project: one on the parasitoids
of the spruce budworm, and one on the egg parasitoids of the hemlock
spruce budworm is a forest insect showing cyclic outbreak and causing
important ecolonomic losses through tree mortality. As a new outbreak
is currently rising in Québec, I'm studying the parasitoids of
species: their phenology, importance, life-history traits, etc.
Understanding how the parasitoids find and exploit their host might
help understanding the dynamic of the spruce budworm outbreaks.
hemlock looper is a moth causing important damages in Canada. My
project aim at better understanding the egg parasitoids causing
important egg mortality in this species. The host exploitation
strategies and reproductive strategies are among the aspects
of life history traits in male parasitoids in a changing world
Most studies on the effects
of climate change in insects use tolerance
to the abiotic environment to predict changes in distribution of
species but ignore its impact on species evolution. The project
studied evolutionary impacts of climate change on a community that is
invaded by a new species. The system studied was the Rhone Valley
of fructiferous Drosophila species (D.
melanogaster, D. simulans and D.
subobscura), all distributed over
this area of France, and their larval parasitoids (Asobara tabida (Braconidae),
Leptopilina boulardi and L. heterotoma (Figitidae)).
tabida and L. heterotoma, that have a palearctic
develop in the three Drosophila species while L. boulardi,
of African origin with a Mediterranean distribution in Europe, only use
first species as hosts. Previous data provide evidence for the
recent spread of
the parasitoid L. boulardi to the north and shows that when
community includes L. boulardi, other parasitoids species
and change phenology. By comparing local populations North from the
invaders with populations south of the front that have been exposed to
invading species for different periods of time, we were able to
evolutionary changes occur in major life history traits of parasitoids.
Objective: The general objective of this
project was to investigate the evolution and adaptation
life-history traits in different populations of Asobara tabida
on both side
of the northern frontier of the distribution of L. boulardi and compare them with that of females.
If male and female life histories and survival are affected
the arrival of L. boulardi, this
would have consequences for population sex ratio and hence for the
dynamics of A. tabida. This
postdoctoral project complemented the ANR project
« Climate change
and evolution of host-parasitoid interaction: from molecules to
communities » by looking at the impact of the changing
(competition, climate, etc) on the evolution of males’ life
history traits, not included in the ANR project.
conducted in collaboration with Joan
Host selection in the
moth Spodoptera littoralis
The choice of host plant is vital for the
survival of an insect. This fact is strongly manifested in the
process, where some insects have evolved to host generalists, while
specialising on a single or a few host species. Different factors can
play an important role in the host selection by a female looking for an
oviposition site. The quality of the plant as a food source, i.e.
larval performance on that plant is highly important: if the larva
cannot develop on that plant, it is not a suitable host. However, many
other factors can play a role: the mortality risks from natural
enemies, the competition from other herbivores (conspecifics or
heterospecifics), the shelter offerred against climatic events, etc.
Every single choice is probably a trade-off between costs and benefits
associated with these different factors.
I am studying the
general question of the impact of mortality risks on choice and
preference in Spodoptera
littoralis, the Egyptian
cotton leaf worm, to understand partially host selection in moths.
Spodoptera littoralis is
distributed pest on a variety of crops throughout a large part of the
warm-temperate and subtropical regions in the Old-world. Among the
hosts are cotton, alfalfa, clover, tomatoes, and many other plants.
even if eggs have been found on these plants, there are not all equally
suitable for the development of the moth and females only prefer a few.
In addition, there is often a discrepancy between the female
oviposition preference and the larval performance. I think that
natural enemies might be an important factor explaining that.
I want to evaluate the importance of natural enemies on host
preference. First of all as a selective pressure, i.e. if plants
offering a better protection are generally preferred by females
ovipositing and by migrating larvae, even if they are lower quality
food. Second, I will look at the actual importance of the physical
presence of the enemies during oviposition. Females might modify their
behaviour (by delaying oviposition, laying less eggs or looking for
another plant) if they perceive enemies, protecting their progeny. In a
similar way, larvae could also migrate to another plant if they
perceive too many enemies on a specific host plant.
This project is a part of a focused effort to
elucidate the coding and modulation of perception and behaviour towards
and non-host plants in the polyphagous moth Spodoptera
littoralis. This program is
called IC-E3 (insect chemical ecology, ethology
and evolution), funded by a 10-years Linnaeus grant. My experimental
give a clear idea of how herbivores are selecting their host. In
comparative evolutionary background will be provided by ongoing work on
and other moths.
work is conducted in collaboration with Fredrik Schlyter, Peter
Anderson and Medhat Sadek.
of the mosquito Aedes aegypti on
attacked by different natural enemies present in their habitat. While
enemies such as parasitoids and predators will kill
their hosts/preys when they successfully attack them, enemies such as
micropredators will not entirely consume their prey.
However, they can still have important consequences on the performance
and ecology of the prey, such as reduced
growth, increased emigration, disease transmission.
objective of this project was to investigate the impact of a
terrestrial micropredator, the
yellow fever mosquito Aedes aegypti, on its unusual invertebrate host,
the Egyptian cotton leaf worm, Spodoptera
developing in presence of mosquitoes showed a slower development and
reached a smaller pupal weight when
compared to a control without mosquitoes, apparently because of a
reduced feeding time for larvae. In addition, larvae
tended to leave the plant in presence of mosquitoes. These results
suggest that mosquitoes act as micropredators and
affects lepidopteran larvae behaviour and development. Ecological
impacts such as higher risks of food depletion and longer
exposure to natural enemies are likely to be costly consequences. The
importance of this phenomenon in nature
– the possible function as last resort when vertebrates are
unavailable – is, however, still unknown.
strategies in the egg parasitoid Trichogramma
In most animals, males are
to have access to an unlimited supply of sperm, while females produce
that are large and costly to produce (Dewsbury 1982). Males’
then be limited only by their capacity to acquire mates, and for males
strategy is to inseminate as many females as possible (Bateman 1948). These
assumptions resulted in a
paradigm in parasitoids: females are monandrous, usually mate locally
emergence patch and expresses optimal behaviours mostly through host
while males are polyandrous, inseminate as many females as possible and
no optimization in havetheir reproductive behaviours.
opportunities are not distributed equally among males, but most males
disperse non sperm-depleted, suggesting
off-patch mating potential.
are able to discriminate between mated females and virgin ones, and
competition risks and/or intensity are important for males that
sperm investment when the number of rivals increases.
- Males express
behaviours enabling them to optimize their patch time
strategies in hymenopteran
Parent investment in their progeny
is an important topic in behavioural ecology and several models have
developed to predict and explain the number of offspring and the sex
(proportion of males) produced by a female. Fisher’s model (1930)
when mating is at random in the population (panmixis), parents should
the same amount of energy in each sex, leading to a 1:1 sex ratio. Hamilton
produced the Local Mate Competition (LMC) model that explains the
female-biased sex ratios in species with structured populations where
occurs locally. In these populations,
sex ratios are female-biased to reduce competition for mating between
Females under LMC lay only as many sons as necessary to mate all their
daughters. When there is more than one foundress on a patch (when
mothers are present), each female lays more sons than needed,
competition for mating between males. Such an increase in the
males enhances the probability that the mother’s genes will
the number of foundresses increases toward infinity, it leads the sex
toward the equality of Fisher.
species with structured
populations, inbreeding frequently occurs. After emergence, females
choose between mating on the patch before dispersing or leaving the
find a mate. In gregarious or quasi-gregarious species, within-patch
frequent, while in solitary species, the females have to leave the host
a mating partner because they are alone at emergence (Godfray 1994).
species can show protandry: males emerge first and wait for females,
their sisters, increasing chances of sibmating (Wiklund &
Fagerström 1977). The LMC theory
mating structure as fully local; no mating occurs outside the natal
However, intermediate situations are probably often encountered in many
parasitoid species. Partial local mating, “an intermediate mating
between panmixis and fully local mating”, seems to be frequent
There is no direct evidence on the occurrence of partial local mating,
indirect comparative evidences in species where both winged and
occur (West & Herre 1998, Fellowes et
of competition on sex allocation was observed for Trichogramma
Riley and Trichogramma pintoi
Voegele. Results show that females of both species lay more males under
intraspecific competition than alone, following the Local Mate
theory, while only T. pintoi modifies
its sex ratio under interspecific competition. Multiparasitism and
habitat could explain this shift in the sex ratio.
Trichogramma minutum, T. pintoi
and Trichogramma turkestanica Westwood
pre-mating dispersion show that most matings occur at the emergence
However, the three species have a potential for off-patch mating,
genetic exchange between sub-populations. These three species were
because they are classified in different groups in the genus.