RESEARCH ACTIVITIES

The research theme I have been working on for the past ten years is at the interface of plant virology, entomology and agronomy. The objective is twofold: (1) to better understand (or even predict) the development of viral epidemics in open field vegetable crops by looking, in particular, for explanatory factors relating to vector population dynamics or viral inoculum, and (2) to design and/or evaluate innovative control methods to reduce virus impact on yield.

My project focuses on open field melon crops. These crops are frequently infected by four aphid-borne viruses which, depending on their relative dynamics and severities, can cause more or less significant quantitative and qualitative yield losses:

Towards a better understanding of viral epidemics: monitoring vector population dynamics

The spread of the majority of phytoviruses depends on their effective transmission from plant to plant through vectors. This “vector” component currently remains a black box in most epidemiological models while it is essential to develop more realistic models for designing relevant control strategies.
In particular, knowledge of vector population dynamics is essential to understand viral outbreaks. In our case, quantitative and qualitative monitoring of winged aphid populations visiting crops will allow us to explore the involvement of different aphid species in the initiation and development of viral outbreaks.
This involves regular sampling (usually daily sampling) using traps selected according to the constraints of the experiment (suction traps or yellow traps for sites without electrical power) and the identification of species by observation of morphological criteria under binocular lens.

Suction trap used to monitor winged insects in sites with electrical power (A) In situ in a melon crop (B) Schematical representation of the suction trap adapted from Pascal et al. 2013 showing its functioning principle and its different parts: Œ (1) vacuum chamber,  (2) air extractor, Ž (3) insect collector,  (4) collecting pot,  (5) chimney rain hat

Yellow pan trap used to monitor winged insects in sites without electrical power. (A) In situ in a tomato crop (B) They are easy to deploy over a large geographic area (for example along the mediterranean basin in the EMERAMB project)

Taxonomic identification of aphids (A) under stereomicroscope, (B) based on morphological characteristics using several dichotomous keys

Since 2010, we have been systematically following both the population dynamics of winged aphids and viral epidemics for all the «melon» trials conducted in Avignon as part of various projects. Considering only the modality common to these projects (field margins with bare soil), nearly 30,000 aphids of 216 different taxa were determined between 2010 and 2019 (Schoeny and Gognalons, 2020).

An example of multi-year monitoring for 3 aphid species known to be vectors of CABYV

Our database is beginning to be sufficiently comprehensive to investigate the relationships between winged aphid population dynamics and viral epidemics.
Thus for CABYV, the search for correlations between these two types of variables revealed significant relationships between the abundance of Aphis gossypii aphids during the first two weeks of the crop and the total AUDPC of CABYV and the estimated parameters of the fitted logistic curves (Schoeny et al., 2020). The existence of these relationships seems to confirm the fact that CABYV is mainly transmitted by Aphis gossypii.  The predictive nature of the relationships is also interesting and suggests that any technique to reduce Aphis gossypii population early could have a positive impact on the CABYV outbreak.

Towards the design of innovative control methods

In collaboration with Nathalie Boissot (INRAE-GAFL Montfavet) I am interested in the coupling between genetic control and cultural practices that reduce bioaggressors in a perspective of sustainability.
This axis of research focuses on the major gene Vat, which confers resistance to colonization by Aphis gossypii and resistance to viruses transmitted by these aphids (Boissot et al., 2016). In the field, this results in a significant reduction in outbreaks of CABYV, a virus transmitted mainly by Aphis gossypii in the persistent mode, but ineffectiveness on outbreaks of WMV, a virus transmitted by other aphid species in the non-persistent mode (Schoeny et al. 2017).

Therefore, the use of Vat is usually coupled with aphicide treatments to limit viral transmission by the non-colonizing "visitor" aphids of melon crops. However, the gradual reduction in the use of plant protection products in crop protection imposed by the evolution of the legislation leads to the search for new strategies to accompany genetic control for the management of bio-aggressors.
The hypothesis we tested is that the implementation of flower strips near to the crop can contribute to the regulation of aphid populations and/or their viruliferous potential, thus increasing the effectiveness and durability of resistance mediated by the Vat gene.
Large-scale experiments to test the effect of the combination of Vat x field margin management (in particular bare soil and flower strips) were conducted for 5 years in Avignon.
Flower strips sown with a mix of these five plant species (cornflower, grass pea, sainfoin, salad burnet and sweet marjoram) displayed a flowering continuum likely to provide a food resource to natural enemies throughout the growing season. Their potential to host/enhance natural enemies was compared to those of bare soil. Most generalist and specialist predators analyzed responded positively to the floral resources displayed. In particular, coccinellid and syrphid fluxes were significantly enhanced near flower margins.
We also showed that flower strips could enhance Vat efficiency to limit CABYV and WMV epidemics.

Another promising area of research concerns techniques that disrupt the installation of pests in crops, including the use of repellent plants. Recent research shows that aromatic plants such as rosemary or French marigold disturb the fecundity and nutritional behaviour of Myzus persicae on pepper (Dardouri et al. 2019; Dardouri et al., 2021).
An assessment of the effect of these service plants on the acquisition and inoculation of persistent and non-persistent viruses is currently underway as part of the MultiServ project.

Aromatic plants repellent towards aphids : (A) rosemary (Rosmarinus officinalis), (B) French marigold (Tagetes patula nana)

Regardless of the strategies considered (chemical, cultural, biological, etc.), vector control remains a challenge due in particular to insufficient knowledge of the dynamics of arrival of vectors and the proportion of them carrying viruses (viruliferous).
As part of the BEYOND project  we will develop molecular tools (qRT-PCR) allowing us to detect/quantify the presence of viruses in their vectors in order to be able to characterize the arrival of viruliferous vectors likely to initiate viral epidemics.

REFERENCES

• Boissot, N., Schoeny, A., Vanlerberghe-Masutti, F. (2016). Vat, an amazing gene conferring resistance to aphids and viruses they carry: from molecular structure to field effects. Frontiers in Plant Science, 7:1420, 1-18. DOI: 10.3389/fpls.2016.01420 HAL INRAE-01512038
• Dardouri, T., Gomez, L., Ameline, A., Costagliola, G., Schoeny, A., Gautier, H. (2021). Non‐host volatiles disturb the feeding behavior and reduce the fecundity of the green peach aphid, Myzus persicae. Pest Management Science, 77, 1705-1713. DOI:10.1002/ps.6190 HAL INRAE-03015172
• Dardouri, T., Gomez, L., Schoeny, A., Costagliola, G., Gautier, H. (2019). Behavioural response of green peach aphid Myzus persicae (Sulzer) to volatiles from different rosemary (Rosmarinus officinalis L.) clones. Agricultural and Forest Entomology, 21 (3), 336-345. DOI: 10.1111/afe.12336 HAL INRAE-02267846
• Pascal, F., Bastien, J.-M., Schoeny, A. (2013). Fabrication d’un piège à aspiration pour la capture des pucerons ailés vecteurs de virus. Cahier des Techniques de l'INRA, 79, 13 p. DOI:10.15454/QFCIRK HAL INRAE-02650564
• Schoeny, A., Desbiez, C., Millot, P., Wipf-Scheibel, C., Nozeran, K., Gognalons, P., Lecoq, H., Boissot, N. (2017). Impact of Vat resistance in melon on viral epidemics and genetic structure of virus populations. Virus Research, 241, 105-115. DOI: 10.1016/j.virusres.2017.05.024 HAL INRAE-01535203 
• Schoeny, A., Gognalons P. (2020). Data on winged insect dynamics in melon crops in southeastern France. Data in Brief 29, 105132. DOI:10.1016/j.dib.2020.105132  HAL INRAE-02623260
• Schoeny, A., Lauvernay, A., Lambion, J., Mazzia, C., Capowiez, Y. (2019). The beauties and the bugs: A scenario for designing flower strips adapted to aphid management in melon crops. Biological Control, 136, 103986, 1-10. DOI: 10.1016/j.biocontrol.2019.05.005 HAL INRAE-02619746
• Schoeny, A., Rimbaud, L., Gognalons, P., Girardot, G., Millot, P., Nozeran, K., Wipf-Scheibel, C., Lecoq, H. (2020) Can winged aphid abundance be a predictor of cucurbit aphid-borne yellows virus epidemics in melon crop? Viruses, 12, 911. DOI:10.3390/v12090911 HAL INRAE-02919776