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.

Click on the figures to enlarge
	Suction trap used to monitor winged insects in sites with electrical power (A) In situ in a melon crop (Photo credit: Alexandra Schoeny, INRAE) (B) Schematical representation of the suction trap adapted from Pascal et al. 2013 showing its functioning principle and its different parts: (1) vacuum chamber, (2) air extractor, (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 (Photo credit: Alexandra Schoeny, INRAE) (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).

Example of multi-year monitoring for 3 aphid species known to be vectors of CABYV. (Click on the figure to enlarge)

Our database is beginning to be sufficiently comprehensive to investigate the relationships between winged aphid population dynamics and viral epidemics. (Click on the figure to enlarge)

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.