Biology subjects

Tougeron, K.

Publications and source records attributed to Tougeron, K..

6 recordsLinked to original sources

bioRxiv2026

The two-component microbial system of the black soldier fly larvae (BSFL) gut: a plastic microbiota in the midgut, but a stable one in the hindgut

Due to their highly polyphagous capacities, black soldier fly (Hermetia illucens) larvae (BSFL) are increasingly valued for their ability to convert organic waste into valuable biomass that can be used for a variety of purposes. These remarkable digestive capabilities are highly dependent on an extremely plastic gut microbiota. However, the distribution and functioning of bacterial communities in the various gut compartments - particularly in the hindgut - remain little understood. In this study, we used a metabarcoding approach based on 16S gene sequencing to investigate the effect of three carbohydrate-rich diets with distinct molecular compositions on the functional diversity of the BSFL gut microbiota. Our results showed that the midgut harbors a highly substrate-sensitive microbiota, with a high abundance of Actinomyces spp., regardless of the substrate. A bacterial diversity oriented toward fatty acid biosynthesis pathways is promoted by starch-rich environment, whereas a lignocellulosic substrate fosters a midgut microbiota dominated by Paenibacillus spp. In contrast, the hindgut exhibits a distinctly stable and homogeneous bacterial composition dominated by Dysgonomonas spp. Overall, our results provide clear evidence of a two-compartment microbial system, in which the midgut primarily serves as a substrate-adaptive primary degradation chamber, while the hindgut functions as a stable terminal compartment for the final processing of residual substrates and the recycling of nutrients. These findings contribute to our understanding of the functional diversity of the bacterial microbiota along the BSFL digestive tract, which is a key factor in explaining this insect's remarkable polyphagous behavior and optimizing its use for industrial purposes.

microbiology↗

bioRxiv2021

Assessing the optimal frequency of early parasitoid releases in an apple orchard to control Dysaphis plantaginea: a proof of concept study

Alternative measures to pesticides to control the rosy apple aphid Dysaphis plantaginea are being developed. Naturally occurring predators and parasitoids often fail to reduce aphid abundance below the economic threshold in orchards, because they are active too late after the aphid first infestation. We tested the efficiency of mass release of two parasitoid species, Aphidius matricariae and Ephedrus cerasicola, early in the season to match the presence of aphid fundatrix (sensitive stages). In this trial focusing on an organic apple orchard, three releases were done either every week or every two weeks to test the effect of the release frequency, during two consecutive years. The number of aphid colonies and aphid number per tree were monitored from late March to late May. Degree-days necessary for parasitoid emergence in the field after release were calculated. We show that a sufficient level of aphid control by parasitoids is reached during the first month of the survey, but control mostly fails during the second part of the monitoring session, for both release treatments, and compared to the neem oil control treatment. The relative effects of release frequencies were different between years probably because of interannual differences in aphid population dynamics and initial infestation in orchards. The field survey and the degree-day model suggest that parasitoid releases, at either frequency, are promising candidates for biological control of the rosy aphid, although the method still needs proper calibration. This conclusion needs to be reinforced by repeating the study in more orchards, but our case study lays the first empirical basis that will help to develop future control methods of aphids by parasitoid releases in apple orchards. We argue that releases should be done one to two weeks before first aphid detection to account for long development times of parasitoids at relatively low temperatures.

ecology↗

bioRxiv2019

Trans-generational effects on diapause and life-history-traits of an aphid parasitoid

Transgenerational effects act on a wide range of insects life-history traits and can be involved in the control of developmental plasticity, such as diapause expression. Decrease in or total loss of winter diapause expression recently observed in some species could arise from inhibiting maternal effects. In this study, we explored transgenerational effects on diapause expression and traits in one industrial and one wild strain of the aphid parasitoid Aphidius ervi. These strains were reared under short photoperiod (8:16 h LD) and low temperature (14 {degrees}C) conditions over two generations. Diapause levels, developmental times, physiological and morphological traits were measured. Diapause levels increased after one generation in the wild but not in the industrial strain. For both strains, the second generation took longer to develop than the first one. Tibia length and wing surface decreased over generations while fat content increased. A crossed-generations experiment focusing on the industrial parasitoid strain showed that offspring from mothers reared at 14 {degrees}C took longer to develop, were heavier, taller with wider wings and with more fat reserves than those from mothers reared at 20 {degrees}C (8:16 h LD). No effect of the mother rearing conditions was shown on diapause expression. Additionally to direct plasticity of the offspring, results suggest transgenerational plasticity effects on diapause expression, development time, and on the values of life-history traits. We demonstrated that populations showing low diapause levels may recover higher levels through transgenerational plasticity in response to diapause-induction cues, provided that environmental conditions are reaching the induction-thresholds specific to each population. Transgenerational plasticity is thus important to consider when evaluating how insects adapt to changing environments.

ecology↗

bioRxiv2018

Effect of diapause on cold-resistance in different life-stages of an aphid parasitoid wasp

To overwinter, insects from mild temperate areas can either enter diapause or remain active. Both strategies involve costs and benefits depending on the environment. In the first case, the emerging individuals will resist winter but have a reduced fitness because diapause entails physiological and ecological costs. In the second case, individuals need to be cold-resistant enough to withstand winter temperatures during their immature and adult stages, but could avoid diapause-associated costs. In mild temperate areas, the cost-benefit balance between the diapause and the non-diapause strategy would likely change in response to climate warming. A trade-off between these two strategies should lead to reduction of diapause expression in some populations. We explored the importance of such trade-off through the comparison of cold resistance capacities among different life stages in diapause and non-diapause individuals in a population of the aphid parasitoid Aphidius ervi (Hymenoptera: Braconidae) originating from western France where a decrease of diapause incidence was recently observed. As a proxy measure of insect physiological cold resistance, the Super Cooling Point (SCP) was determined for non-diapausing and diapausing prepupae and adults that went through prepupal diapause or not. Diapausing and non-diapausing prepupae were equally cold-resistant (-24.20 {+/-}0.30{degrees}C vs. -24.74 {+/-}0.36{degrees}C, respectively), and overall more resistant than adults. Adults that went through diapause as prepupae were less cold resistant (-17.85 {+/-}1.10{degrees}C) than adults that have not undergone through diapause (-21.10 {+/-}0.54{degrees}C). We also found that diapausing prepupae and adults that have undergone diapause were lighter than their non-diapausing counterparts, at a comparable size, suggesting higher energetic expenses during diapause. These results suggest a trade-off between diapause expression in prepupae and cold resistance and life-history-traits in adults. We conclude that selection could favor insects that do not enter diapause and thus avoid its associated costs while taking advantage at exploiting the mild winter environment.

ecology↗

bioRxiv2018

Rapid responses of winter aphid-parasitoid communities to climate warming

Consequences of environmental fluctuations, including those associated with climate changes, can have a knock-on effect from individual to community scale. In particular, changes in species seasonal phenology can modify the structure and composition of communities, with potential consequences on their functioning and the provision of ecosystem services. In mild climate areas, aphids can be present in cereal fields throughout the winter, which allows aphid parasitoids to remain active. Using a nine-year dataset of aphid-parasitoid winter trophic webs in cereal fields of Western France, we report that the community structure and composition that prevailed before 2011 have recently shifted toward a more diversified community, with the presence of two new braconid parasitoid species (Aphidius ervi and Aphidius avenae), a few hyperparasitoid species and one aphid species (Metopolophium dirhodum). Increases in minimal winter temperatures and the frequency of frost events across the years partially explain observed community changes. Strong bottom-up effects from the relative abundances of aphid species also determine the relative abundance of parasitoid species each winter. Strong compartmentalization in parasitoid preference for host is reported. We suggest the recent modifications in parasitoid community composition to be linked to shifts in diapause expression (reduction or arrest of the use of winter diapause) and to host availability throughout the year. We highlight the implications for natural biological control in cereal fields. Perspectives are proposed to predict the composition of future host-parasitoid communities in the climate change context.

ecology↗

bioRxiv2018

Sex makes them sleepy: change in host reproductive status induces diapause in parasitoids

When organisms coevolve, any change in one species can induce phenotypic changes in traits and ecology of the other species. The role such interactions play in ecosystems is central, but their mechanistic bases remain underexplored. Upper trophic level species have to synchronize their life-cycle to both abiotic conditions and to lower trophic level species phenology and phenotypic variations. We tested the effect of host seasonal strategy on parasitoid diapause induction by using a holocyclic clone of the pea aphid Acyrthosiphon pisum producing asexual and sexual morphs that are viviparous females (i.e. laying embryos) and oviparous females (laying eggs), respectively, the latter being only present at the end of the growing season. Aphidius ervi parasitoids from populations of contrasted climatic origin (harsh vs. mild winter areas) were allowed to parasitize each morph in a split-brood design and developing parasitoids were next reared under either fall-like or summer-like temperature-photoperiod conditions. We next examined aspects of the host physiological state by comparing the relative proportion of forty-seven metabolites and lipid reserves in both morphs produced under the same conditions. We found that oviparous morphs are cues per se for diapause induction; parasitoids entered diapause at higher levels when developing in oviparous hosts (19.4 {+/-} 3.0%) than in viviparous ones (3.6 {+/-} 1.3%), under summer-like conditions (i.e., when oviparous aphids appear in the fields). This pattern was only observed in parasitoids from the harsh winter area since low diapause levels were observed in the other population, suggesting local adaptations to overwintering cues. Metabolomics analyses show parasitoids response to be mainly influenced by the hosts physiology, with higher proportion of polyols and sugars, and more fat reserves being found in oviparous morphs. Host quality thus varies across the seasons and represents one of the multiple environmental parameters affecting parasitoid diapause. Our results underline strong coevolutionary processes between hosts and parasitoids in their area of origin, likely leading to phenological synchronization, and we point out the importance of such bottom-up effects for trait expression, and for the provision of ecosystem services such as biological control in the context of climate change.

ecology↗