Véronique Martel - Scientific researcher

Research Projects

Present researches:

Previous researches:

Present researches:
Ecology of forest insects' parasitoids
View from a hemlock looper outbreak near Quebec citySpruce budworm larvaA spruce budworm outbreak in Quebec

My researches currently focus on two main project: one on the parasitoids of the spruce budworm, and one on the egg parasitoids of the hemlock looper.

The 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 this 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.

The 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 investigated.

Natural Resources Canada

Previous researches:

Evolution of life history traits in male parasitoids in a changing world
Asobara tabidaMating of a tethered femaleTestesWing and leg

Most studies on the effects of climate change in insects use tolerance to the abiotic environment to predict changes in distribution of individual species but ignore its impact on species evolution. The project proposed  studied evolutionary impacts of climate change on a community that is currently invaded by a new species. The system studied was the Rhone Valley community 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)). Asobara tabida and L. heterotoma, that have a palearctic distribution, develop in the three Drosophila species while L. boulardi, a species of African origin with a Mediterranean distribution in Europe, only use the two first species as hosts. Previous data provide evidence for the recent spread of the parasitoid L. boulardi to the north and shows that when the community includes L. boulardi, other parasitoids species become scarce and change phenology. By comparing local populations North from the front of invaders with populations south of the front that have been exposed to the invading species for different periods of time, we were able to document how evolutionary changes occur in major life history traits of parasitoids.

Objective: The general objective of this project was to investigate the evolution and adaptation of males’ 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 differentially by the arrival of L. boulardi, this would have consequences for population sex ratio and hence for the population 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 environment (competition, climate, etc) on the evolution of males’ life history traits, not included in the ANR project.


This was conducted in collaboration with Joan van Baaren.

CNRSCARENUniversité Rennes IEcobio

Previous researches:

Host selection in the moth Spodoptera littoralis

Female on cottonSpodoptera cultureLarva on cottonEggs on clover

    The choice of host plant is vital for the survival of an insect. This fact is strongly manifested in the evolutionary process, where some insects have evolved to host generalists, while others are 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 a widely distributed pest on a variety of crops throughout a large part of the warm-temperate and subtropical regions in the Old-world. Among the reported hosts are cotton, alfalfa, clover, tomatoes, and many other plants. However, 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 host 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 work will give a clear idea of how herbivores are selecting their host. In addition, comparative evolutionary background will be provided by ongoing work on beetles and other moths.

This work is conducted in collaboration with Fredrik SchlyterPeter Anderson and Medhat Sadek.
Insect Chemical Ecology, Ethology and Evolution             

Previous researches:

Micropredation of the mosquito Aedes aegypti on a caterpillar
By Benjamin Hornoy
Aedes aegypti
Setup with cotton plants

Organisms are 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.

The 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 littoralis.

Larvae 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.

This work was conducted in collaboration with Fredrik Schlyter, Peter Anderson and Rickard Ignell.
Insect Chemical Ecology,  Ethology and Evolution             Sveriges Landbruskuniversitet

By Benjamin Hornoy

Previous researches:

Males reproductive strategies in the egg parasitoid Trichogramma turkestanica

Trichogramma mating
Seminal Vesicles
Female spermatheca
Trichogramma sperm
    In most animals, males are assumed to have access to an unlimited supply of sperm, while females produce few eggs that are large and costly to produce (Dewsbury 1982). Males’ fitness should then be limited only by their capacity to acquire mates, and for males the best 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 on the emergence patch and expresses optimal behaviours mostly through host selection while males are polyandrous, inseminate as many females as possible and express no optimization in havetheir reproductive behaviours.

However, some data suggest that male insects optimize their reproductive decisions and behaviours to maximize their lifetime fitness. It is now recognized that males’ gametes production induces non-trivial costs and that males should use their sperm supply with parsimony (Walker 1980; Dewsbury 1982; Svärd 1985, Simmons 2001). Because sperm is allocated in packages called ejaculates and that their cost is greater than that of individual sperm (Williams 1966; Trivers 1972; Dewsbury 1982), males can gain by carefully allocating both sperm and ejaculates. In addition, males can also be sperm-limited, increasing the benefits of allocating sperm optimally. Males can be prospermatogenic when they emerge with all their sperm stock or synspermatogenic if they produce sperm during their adult life (Boivin et al. 2005). Prospermatogenic males cannot produce sperm during their adult life and may thus become sperm-depleted when all their stock has been transferred.

    I  investigated different aspects of males’ reproductive strategies, mainly sperm and time allocation, in the egg parasitoid Trichogramma turkestanica Meyer (Hymenoptera: Trichogrammatidae). From the results, it appears that time- and sperm-limited male T. turkestanica are not simply maximizing the number of females inseminated, but rather maximize their lifetime fitness by optimizing sperm and patch time allocation. Here are the main results. However, you can consult my PhD thesis for more details.

  • Mating opportunities are not distributed equally among males, but most males disperse non sperm-depleted, suggesting off-patch mating potential.
  • Males are able to discriminate between mated females and virgin ones, and prefer virgin ones. 
  • Sperm competition risks and/or intensity are important for males that decrease their sperm investment when the number of rivals increases.
  • Males express behaviours enabling them to optimize their patch time exploitation. 
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Previous researches:

Reproductive strategies in hymenopteran egg parasitoids

By Franz Vanoosthuyze

Trichogramma pintoi
Trichogramma minutum
Trichogramma turkestanica
Trichogramma rearing

    Parent investment in their progeny is an important topic in behavioural ecology and several models have been developed to predict and explain the number of offspring and the sex ratio (proportion of males) produced by a female. Fisher’s model (1930) predicts that when mating is at random in the population (panmixis), parents should invest the same amount of energy in each sex, leading to a 1:1 sex ratio. Hamilton (1967) later produced the Local Mate Competition (LMC) model that explains the occurrence of female-biased sex ratios in species with structured populations where mating occurs locally. In these populations, sex ratios are female-biased to reduce competition for mating between kins. 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 multiple mothers are present), each female lays more sons than needed, increasing competition for mating between males. Such an increase in the proportion of males enhances the probability that the mother’s genes will disperse. When the number of foundresses increases toward infinity, it leads the sex ratio toward the equality of Fisher.

In species with structured populations, inbreeding frequently occurs. After emergence, females have to choose between mating on the patch before dispersing or leaving the patch to find a mate. In gregarious or quasi-gregarious species, within-patch mating is frequent, while in solitary species, the females have to leave the host to find a mating partner because they are alone at emergence (Godfray 1994). Gregarious species can show protandry: males emerge first and wait for females, mainly their sisters, increasing chances of sibmating (Wiklund & Fagerström 1977). The LMC theory considers mating structure as fully local; no mating occurs outside the natal patch. However, intermediate situations are probably often encountered in many parasitoid species. Partial local mating, “an intermediate mating structure, between panmixis and fully local mating”, seems to be frequent (Hardy 1994). There is no direct evidence on the occurrence of partial local mating, but only indirect comparative evidences in species where both winged and wingless males occur (West & Herre 1998, Fellowes et al. 1999).

    Impact of competition on sex allocation was observed for Trichogramma minutum Riley and Trichogramma pintoi Voegele. Results show that females of both species lay more males under intraspecific competition than alone, following the Local Mate Competition theory, while only T. pintoi modifies its sex ratio under interspecific competition. Multiparasitism and natural 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 site. However, the three species have a potential for off-patch mating, allowing genetic exchange between sub-populations. These three species were chosen because they are classified in different groups in the genus.

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