Host plant specialization matters in the epidemiology of Wolbachia across phytophagous wasps (Hymenoptera: Torymidae)

Host plant specialization matters in the epidemiology of Wolbachia across phytophagous wasps (Hymenoptera: Torymidae). 8. International Wolbachia Conferenc

L’impact des insectes parasites des graines sur les capacités de régénération naturelle des peuplements de cèdre de l’Atlas et de sapin pectiné en Languedoc-Roussillon

La régénération naturelle des peuplements forestiers est soumise à diverses contraintes environnementales, parmi lesquelles, les insectes ravageurs des cônes et des graines jouent un rôle majeur. Depuis 2004, une étude a été menée sur des cédraies et sapinières de la région Languedoc-Roussillon. Les résultats montrent que ces insectes peuvent causer des pertes importantes de graines et, localement, l’impact peut être important. Certaines mesures sanitaires et le maintien du suivi des populations de ravageurs sont préconisées pour mieux anticiper et limiter l’impact de ces insectes sur la régénération naturelle des peuplementsNatural regeneration of forest stands is subject to various environmental constraints. Among these, cone and seed insects are often considered the main biotic factor during the pre-dispersal phase. Since 2004, we have estimated the impact of these pests in 11 Atlas cedar and 11 fir stands in the Languedoc-Roussillon region. The results show that these insects can cause a significant loss of seeds that would otherwise contribute to stand regeneration. Indeed, seed pests of the genus Megastigmus were responsible for the loss of 13% and 9% of the seeds in fir and Atlas cedar stands, respectively. Locally, the impact of these insects can be substantial, reaching 34% of the yearly seed production in some fir stands and 39% in Atlas cedar stands. Considering individual trees, up to 85% of the seeds can be infested, which equates to a nearly complete loss of regenerative potential for a given tree in the year of the infestation. Mixed stands appear to be more infested than pure stands. This study has also demonstrated the host transfer capacity of a seed insect from true cedar to fir. This transfer, along with the possibility of the invasion of Languedoc-Roussillon true cedar stands by a seed insect recently introduced in the neighboring region, illustrates a dynamic system whose evolution is hard to predict. Some pest management measures and the maintenance of population surveys are suggested to better anticipate and limit the impact of these insects on stand regeneratio

Ecoregional Patterns of Spruce Budworm—Wildfire Interactions in Central Canada’s Forests

Wildfires and outbreaks of the spruce budworm, Choristoneura fumiferana (Clem.), are the two dominant natural disturbances in Canada’s boreal forest. While both disturbances have specific impacts on forest ecosystems, it is increasingly recognized that their interactions also have the potential for non-linear behavior and long-lasting legacies on forest ecosystems’ structures and functions. Previously, we showed that, in central Canada, fires occurred with a disproportionately higher frequency during a ‘window of opportunity’ following spruce budworm defoliation. In this study, we use Ontario’s spatial databases for large fires and spruce budworm defoliation to locate where these two disturbances likely interacted. Classification tree and Random Forest procedures were then applied to find how spruce budworm defoliation history, climate, and forest conditions best predict the location of such budworm–fire interactions. Results indicate that such interactions likely occurred in areas geographically bound by hardwood content in the south, the prevalence of the three major spruce budworm host species (balsam fir, white spruce and black spruce) in the north, and climate moisture in the west. The occurrence of a spruce budworm–fire interaction inside these boundaries is related to the frequency of spruce budworm defoliation. These patterns provide a means of distinguishing regions where spruce budworm attacks are likely to increase fire risk

Identifying spatial relationships at multiple scales: principal coordinates of neighbour matrices (PCNM) and geostatiscal approaches

International audienc

How to invade a Mediterranean forest ecosystem ? A lesson from seed insects in French Cedrus atlantica (Pinaceae) forests

Worldwide exchange of tree materials is a major factor favouring insects’ invasions in forest ecosystems through considerable extensions of their distribution ranges. Here we describe the biological and ecological mechanisms involved in the recent invasion of southeastern French cedar (Cedrus atlantica) stands by the invasive seed predator Megastigmus schimitscheki (Hymenoptera: Torymidae). Despite the presence of resident direct competitor (M. pinsapinis), French M. schimitscheki populations display a continuous increase in abundance due to multiple adequations of its life cycle with its new environment. Specifically, adults emergence is well synchronized with the timing of cedar’s fructification and interannual variations in resource abundance may be counterbalanced by prolonged diapause, temporally dispersing individuals of a cohort. Adult emergence and realized fecundity in M. schimitscheki were found significantly earlier and higher (respectively) than in M. pinsapinis, suggesting enhanced abilities of M. schimitscheki to exploit local resources compared to M. pinsapinis. Consequently, we observe recurrent local exclusion by the invasive species. Population genetics of M. schimitscheki also suggest high long distance dispersal abilities. Our analysis of key components of both local and regional dynamics of this species shed a critical light on the processes involved in a successful insect invasion in a French Mediterranean ecosyste

Les risques sanitaires consécutifs à l'été 2003 à la lumière de la littérature

National audienc

Temporal population genetics of time travelling insects: a long term study in a seed-specialized wasp.

Many animal species experiencing spatial or interannual fluctuations of their environment are capable of prolonged diapause, a kind of dormancy that extends over more than one year. Such a prolonged diapause is commonly perceived as a temporal demographic refuge in stochastic environments, but empirical evidence is still lacking of its consequences on temporal population genetic structures. In this long-term study, we investigated how a particular pattern of prolonged diapause may influence the temporal population genetics of the invasive seed-specialized wasp Megastigmus schimitscheki (Hymenoptera: Torymidae) in southeastern France. We characterized the diapause strategy of M. schimitscheki using records of emergence from diapause in 97 larval cohorts, and we conducted a temporal population genetic study on a natural invasive wasp population sampled during ten consecutive years (1999-2008) using polymorphic microsatellite markers. We found that M. schimitscheki can undergo a prolonged diapause of up to five years and displays two main adult emergence peaks after two and four years of diapause. Such a bimodal and atypical pattern did not disrupt temporal gene flow between cohorts produced in even and in odd years during the period of the study. Unexpectedly, we found that this wasp population consisted of two distinct genetic sub-populations that strongly diverged in their diapause strategies, with very few admixed individuals. One of the sub-populations displayed both short and prolonged diapause (2 and 4 years respectively) in equal proportions, whereas the other sub-population displayed mainly short diapause. This study provided empirical evidence that prolonged diapause phenotypes can substantially contribute to reproduction and impact temporal genetic structures. Prolonged diapause is likely to act as both demographic and genetic refuges for insect populations living in fluctuating environments

Microsatellite data for ten consecutive cohorts of the seed wasp Megastigmus schimitscheki sampled in southeastern France.

This file presents the genotypes of 470 females of Megastigmus schimitscheki sampled in 10 successive cohorts (1999-2008) at Mont Ventoux, southeastern France (44.141389°N 5.386111°E). The sampled individuals displayed either short (SD) or prolonged (PD) diapause, which lasted 2 and 4 years, respectively. Emerging females of the SD or the PD phenotypes were genotyped at 9 microsatellite loci : MS1-alpha, MS2-162, MW-34, MS1-110, MS3-98, MS3-105, MS3-99, MS1-43 and MS3-91. Electrophoresis of PCR products was performed on an ABI3730 XL sequencer and the microsatellite profiles were analysed in the GenMapper software version 4.

Data from: Temporal population genetics of time travelling insects: a long term longitudinal study in a seed-specialized wasp

Many animal species experiencing spatial or interannual fluctuations of their environment are capable of prolonged diapause, a kind of dormancy that extends over more than one year. Such a prolonged diapause is commonly perceived as a temporal demographic refuge in stochastic environments, but empirical evidence is still lacking of its consequences on temporal population genetic structures. In this long-term study, we investigated how a particular pattern of prolonged diapause may influence the temporal population genetics of the invasive seed-specialized wasp Megastigmus schimitscheki (Hymenoptera: Torymidae) in southeastern France. We characterized the diapause strategy of M. schimitscheki using records of emergence from diapause in 97 larval cohorts, and we conducted a temporal population genetic study on a natural invasive wasp population sampled during ten consecutive years (1999–2008) using polymorphic microsatellite markers. We found that M. schimitscheki can undergo a prolonged diapause of up to five years and displays two main adult emergence peaks after two and four years of diapause. Such a bimodal and atypical pattern did not disrupt temporal gene flow between cohorts produced in even and in odd years during the period of the study. Unexpectedly, we found that this wasp population consisted of two distinct genetic sub-populations that strongly diverged in their diapause strategies, with very few admixed individuals. One of the sub-populations displayed both short and prolonged diapause (2 and 4 years respectively) in equal proportions, whereas the other sub-population displayed mainly short diapause. This study provided empirical evidence that prolonged diapause phenotypes can substantially contribute to reproduction and impact temporal genetic structures. Prolonged diapause is likely to act as both demographic and genetic refuges for insect populations living in fluctuating environments

Development of a New TRIPLEX-Insect Model for Simulating the Effect of Spruce Budworm on Forest Carbon Dynamics

The spruce budworm (SBW) defoliates and kills conifer trees, consequently affecting carbon (C) exchanges between the land and atmosphere. Here, we developed a new TRIPLEX-Insect sub-model to quantify the impacts of insect outbreaks on forest C fluxes. We modeled annual defoliation (AD), cumulative defoliation (CD), and tree mortality. The model was validated against observed and published data at the stand level in the North Shore region of Québec and Cape Breton Island in Nova Scotia, Canada. The results suggest that TRIPLEX-Insect performs very well in capturing tree mortality following SBW outbreaks and slightly underestimates current annual volume increment (CAI). In both mature and immature forests, the simulation model suggests a larger reduction in gross primary productivity (GPP) than in autotrophic respiration (Ra) at the same defoliation level when tree mortality was low. After an SBW outbreak, the growth release of surviving trees contributes to the recovery of annual net ecosystem productivity (NEP) based on forest age if mortality is not excessive. Overall, the TRIPLEX-Insect model is capable of simulating C dynamics of balsam fir following SBW disturbances and can be used as an efficient tool in forest insect management