The association of Salicaceae and Aphrophoridae A potential Xylella fastidiosa-based threatening pathosystem for European temperate areas
Casarin N.1, Hasbroucq S.2, Glibert A.1, Carestia G.1, Bragard C.1, Grégoire J.-C.2 1Earth&Life Institute (ELI) Applied Microbiology, UCLouvain, Louvain-la-Neuve, Belgium 2Spatial Epidemiology lab (SpELL), Université libre de Bruxelles, Brussels, Belgium Introduction THE RISK OF XF FOR NORTHERN EUROPEAN TEMPERATE REGIONS SHOULD NOT BE UNDERESTIMATED
EFSA PLH 2018 EFSA PLH 2019
Xf subsp. multiplex in cooler climates, Potential insect vectors and climatic suitability modelling potential hosts across all Europe Climate change and many from Northern regions may never have met the bacterium Homologous recombination Uncertainties… Numerous introductions in Europe
2 Introduction
RIPARIAN AREAS AS POTENTIAL XF RESERVOIR Land adjacent to watercourses and water bodies
Role in the epidemiology of Pierce’s disease (PD) in California Incidence of PD higher near riparian areas (Purcell 1974) Key habitat of some vectors (Purcell 1975) courtesy of Alexander Purcell, UC IPM and Matt Daugherty Host plants of X. fastidiosa (Purcell & Saunders 1999) R
Same potential role in Europe? Investigation in Belgium Communication channels between different landscapes Presence of potential insect vectors Common riparian tree layer = potential hosts ?
Survey on Salicaceae
Belgian landscape Google view 3 Introduction MECHANICAL INOCULATIONS REVEAL THE POTENTIAL OF THE SALICACEAE AS XF HOSTS
Inoculation at 22°C and 28°C of Salix alba, S. caprea, Populus tremula & P. canescens with KLN59.3 GFP-tagged strain provided by S. Lindow.
Monitoring movement of Xf by PCR 1-3-6 X.fastidiosa months post-inoc. Persistence & spread of Xf after 9 months GFP-tagged X. fastidiosa KLN59.3 in stems and roots in S. alba (1m) and in observation by confocal microscopy in P. tremula (70 cm) confocal microscopy P. tremula Clear symptoms for P. tremula, S. alba asymptomatic?
Mechanically inoculated willows in controlled biosafety conditions
Cfr poster on mechanical inoculations https://doi.org/10.5281/ zenodo.4682127 Symptoms on P.tremula after inoculation 4 Introduction
APHROPHORA SALICINA: ASSOCIATED WITH SALICACEAE; PHILAENUS SPUMARIUS: POLYPHAGOUS EUROPEAN VECTOR
EFSA opinion 2015 on potential vectors for Europe Aphrophora salicina very abundant on Salicaceae: Life cycle, host plants, abundance and distribution ca 600 adults counted on a 6-m high willow, with in Belgium (Hasbroucq et al., 2019) 1000 twigs Presence in riparian areas Philaenus spumarius, polyphagous, widely distributed
1 to 2 <10 10 to 50 >50
Abundance map of Aphrophora salicina in Belgium (1h net swipes at ground level) Distribution of Philaenus spumarius in Belgium (Hasbroucq et al., 2019) 5 recapture Methods FLIGHT-MILL & MARK-RELEASE-RECAPTURE TO STUDY DISPERSION CAPACITY
FLIGHT MILL MARK-RELEASE-RECAPTURE
Overestimation of dispersion capacity Underestimation of dispersion capacity - : Artificial flight performance - : Interception distances, limited by + : Estimation of the probability distribution recapture strategy and by area growing with of flight distances, important to shape distance from the releasing point dispersal kernel for modelling + : Mainly to understand behaviour of + : Compare effects of different treatments insects in the field
On Aphrophora salicina & Philaenus spumarius at 3 physiological states July: mating period August: egg-laying period September: end of life Aphrophora salicina Philaenus spumarius 6 Methods MARK-RELEASE-RECAPTURE EXPERIMENT
2 sites : rural (Genappe) and urban (Brussels) 250 to 1000 insects collected and marked with fluorescent powder Released at one point on a take-off platform Survey every day of the week following the release: naked eyes/binocular, sweeping nets, telescopic net
Recapture after one month sampling and The two sites (Google Earth) checking with UV lamp Yellow traps within 100m radius of release point
Telescopic net
Take-off platform at the release point 1 day 4 days 7 days 1 month • P. spumarius • A. salicina
7 Results OVERVIEW OF MARK-RELEASE-RECAPTURE IN JULY: APHROPHORA SALICINA
RURAL SITE URBAN SITE
RecaptureDAYJulyDAY 3713_92541 insects DAYDAYDAYRecaptureJune 41729_1000 insects afterreleased1 afterreleased1 month month Max. dist.
No insect Max. dist.
8 Results OVERVIEW OF MARK-RELEASE-RECAPTURE IN JULY: PHILAENUS SPUMARIUS RURAL SITE URBAN SITE DAYDAYRecaptureJuly 725 13_871 insects DAYDAYRecapture 2713 July 7_870 insects afterreleased1 after 1 released month month
Max. Max. dist. dist.
9 Results MARK-RELEASE-RECAPTURE: RESULT OVERVIEW Aphrophora salicina Philaenus spumarius
Rural Urban Rural Urban
Max dist.
Max dist.
Max dist.
releasing point[m] releasing releasing point[m] releasing
Max dist.
from
from
Distance Distance
July Aug Sept July Aug Sept July Aug Sept July Aug Sept
Mainly on Salicaceae Mainly herbaceous, some on Salicaceae First flight Mostly jumping Rural site: general 1-10m, > 40 m in July First jump: 1 m Urban site: 1-2 m on the first willow available Do not cross the boulevard Do not cross the boulevard
10 Methods
STEPS OF FLIGHT-MILL ASSAYS
1 2 3 4
Collection of wild Flight-mill recording Break: 24h Flight-mill recording insects (50-60 ind. for 2h30 feeding & resting for 2h30 for each period) and FIRST FLIGHT on a host plant SECOND FLIGHT sex identification SESSION SESSION
11 Results MORE FLIGHTS AMONG A. SALICINA THAN AMONG P. SPUMARIUS MORE FLIGHTS IN JULY THAN IN SEPTEMBER
A. salicina P. spumarius Flight rate of first session illustrated here a ab bc bc c c Flight: twice as many A. salicina 100% as P. spumarius 90% 80% Flight rate significantly decreases 70% through the season 60% More flights during mating period 50% 40% No significant differences between 30% male and female 20% 10% ca 50% mortality between 1st 0% and 2nd flight session July Aug Sept July Aug Sept Flying insects Stationary insects Flight rate during second session ca. 40% Reg.log => linear contrasts
12 Results DISTANCES TRAVELLED DURING 2H30 WERE GREATER FOR A. SALICINA
Distance for all flights A. salicina P. spumarius
1st SESSION n=96 2nd SESSION n=18 Mean value
in 2h30 [m] 2h30in
in 2h30 [m] 2h30in
travelled
travelled
Distance Distance
Significant difference between A. salicina and P. spumarius at 1st flight (W=1691, p<0.001)
Maximal distance during 2h30: . 4423 m: A. salicina females in August . 1542 m: P. spumarius females in July
Low activity among P. spumarius, except females in July 13 Discussion
A. salicina, abundant on Salicaceae, can act as long and medium-distance connector
Salicaceae
A. salicina
14 Discussion
Salicaceae are potential hosts of Xf, meaning that A. salicina could be a potentially serious vector
Salicaceae ?
A. salicina
X. fastidiosa
15 Discussion
P. spumarius, short connector but polyphagous, could take over on a multitude of plant species
Salicaceae ?
A. salicina
X. fastidiosa
P. spumarius
16 THANK YOU FOR YOUR ATTENTION
Contributions Séverine Hasbroucq Audrey Glibert Gabriel Carestia Amandine Géradin Lena Pesenti Pr. Claude Bragard Pr. Jean-Claude Grégoire
Funds Xfast project funded by SPF santé Publique Noemi Casarin, Fellow of FRIA (FNRS)
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