Présentation IIRB 2024 Corentin Sochard - ÌTB

1. Corentin Sochard – 79th IIRB Congress – 27/02/2024

2. Life cycle & spatial distribution
27 February 2024 79th IIRB Congress
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3. Life cycle of Lixus juncii
3
1 generation / year
Further
information
Sowing
Harvest
Development
cycle of the
beetroot weevil
Lixus juncii
1 female =
100 - 350 eggs
4 instars
Pupation in the
stem/petiole/root
27 February 2024 79th IIRB Congress
Seed bearers
Sugar beet
Root yield loss:
Galleries ≈ 5-10%
+ Rhizopus: up to 100%
Seed yield loss:
Stem desiccation ≈ 30%
Reduced seed size
Damage

4. Hypothetic migration
pathways
(population genetic not yet
Spatial distribution and expansion
Expansion steps:
• 2000: weevils in south France on seed
bearers
• 2010: Migration to sugar beet in Limagne
(Center of France)
• 2015 - 2018: Colonization of the
production areas south and east of Paris
• 2022: Migration further north
4
27 February 2024 79th IIRB Congress
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1
1
1
3
4
2
3
3
4

5. Ubelix project
Studying weevil biology and control strategies
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27 February 2024 79th IIRB Congress

6. Repulsion
Attraction
Push-pull in the beetroot system
-
+
Intercrops
Trap crops /
attractive & tolerant varieties
+
Ubelix project
6
Problematic: Could a push-pull strategy work
against Lixus juncii using intercropping?
Partners:
(2022 – 2025)
Reducing damage with 3 complementary methods:
• Use of intercrops to repulse weevils from the beetroots
• Use of trap crops or attractive varieties to attract it
elsewhere
• Identification of attractive but tolerant varieties
and analysis of their metabolic profile
+ Investigation of L. juncii biology / life
cycle
27 February 2024 79th IIRB Congress

7. Biology of Lixus juncii
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27 February 2024 79th IIRB Congress

8. Questions on biology / life cycle
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Reproduction
When and where do they
mate?
Can we disturb it?
Arrival in spring
Where do they hide
before field colonization?
27 February 2024 79th IIRB Congress
Overwintering
Where do they
hide during
winter?

9. Sexual maturity & reproduction
Can we use a control strategy based on sexual confusion?
• When and where does mating occur?
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Female dissection
LEE
Sexing
287 dissected females
• 66% mature
• 80% mated
27 February 2024 79th IIRB Congress
Weevils captures in the field
(1st to 15th May 2022)
Sexual confusion strategy
unlikely efficient
Part of the Ubelix project

10. Overwintering
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No weevil found
Sampling around a very infested site in 2022:
• 5 environment types
• 3 sampling methods
• 4 samples / environment
Can we anticipate next year
pressure?
• Where do they hide during winter?
27 February 2024 79th IIRB Congress
Border
Grove
Rapeseed
Grove
Meadow
Sugar beet
2022
Sampling methods
Sieving & debarking
Sweep-netting
LEE
LEE
LEE LEE
Part of the Ubelix project

11. Arrival in spring
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Sugar beet 2022
/ wheat 2023
Border
Grove
Meadow
Rapeseed
Wheat
Capture methods
Emergence traps
Yellow pan traps
Pitfall traps
Sweep-netting
Border
Border
4 weevils captured (3 ♀ + 1 ♂)
between the 2nd to 9th May
16 Sweep-net transects
Weekly sampling
from April to mid-May
4 capture methods
10 emergence traps
11 yellow pan traps
8 pitfall traps
1 female
2 females (1 mated)
1 male
Can we anticipate next year pressure?
• Where do they hide during winter?
• Where do they hide before field
colonization?
27 February 2024 79th IIRB Congress
Part of the Ubelix project
LEE

12. Ecology of Lixus juncii
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27 February 2024 79th IIRB Congress

13. Study of L. juncii ecology
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Environmental effects on
development and
survival
Influence of water input
Survival of immature weevils
Communities of
beneficial insects
Diversity &
abundance
Parasitism rate
27 February 2024 79th IIRB Congress

14. Influence of irrigation/rain
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Less galleries
when irrigated
 No difference
in egg laying
Count of
laying holes
In 2023 (rainy year):
more nymphs observed in the petioles
Count of
galleries in root
Does the environment influence weevil's development inside beetroots?
2 hypothesis:
• Water increase larval mortality
• Water decrease migration in the
root
27 February 2024 79th IIRB Congress

15. Survival of immature weevils
Campaigns 2022 & 2023:
• 708 petioles sampled
• 1293 laying holes
considered
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Egg of L. juncii
Larvae of L. juncii
27 February 2024 79th IIRB Congress
Mortality of weevil
stages in the petiole
26%
14%
60%
Larval death:
35%
2023
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Larval death:
58%
2022
19%
68%
13%
Egg mortality
Larval mortality
Survival

16. 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Mortality due to parasitism
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Egg mortality
Larval mortality
Survival
Killed by a parasitoid
Missing or dead
with unknown
reason
42%
27%
31%
Causes of larval
mortality
Results 2022
9% to 60%
depending on site
Necrosed L. juncii larvae
Parasitoid at different
developmental stages
Larva
Nymph (free) Nymph (cocoon)
Parasitoid traces
Emergence hole
Egg parasitoids (insects or traces)
19%
68%
13%
27 February 2024 79th IIRB Congress
Mortality of weevil
stages in the petiole

17. Communities of beneficial parasitoids
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Web article on
parasitoid captures
New species in 2023
Egg parasitoids
Parasitoïd diptera
Eupelmida
e
Cocoon (nymph)
Eurytoma
curculionu
m
♀
Stenomalin
a gracilis
♀
♀ Bracon
intercessor
Main species
(75% of identified parasitoids)
2022: 30% of Lixus larvae parasitized
27 February 2024 79th IIRB Congress
Endromopoda
detrita
♂
2023: 15% of Lixus larvae
parasitized

18. Current & future research thematic
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27 February 2024 79th IIRB Congress
Irrigation
Biocontrol
Beneficial
insects
Conventional
insecticides
Tolerant
varieties
Intercrop
s
Trap crops
Rhizopus
control
Overwinterin
g
Reproduction
Sowing
Harvest
Sexual
perturbation
Types of thematic
Biology / life cycle
Control methods
Spatial
dynamic
Populatio
n genetic
Spring arrival
Pheromones
traps

19. 79th IIRB Congress – 27/02/2024