1) The study examined the effects of different cover crop planting systems on macrofauna diversity in upland rice fields in Madagascar, where white grubs are a major pest problem. 2) Results showed that systems with hairy vetch as a cover crop had the highest macrofauna abundance but did not control white grubs effectively. Systems with radish as a cover crop showed promising control of phytophagous white grubs while not reducing macrofauna diversity or abundance. 3) The researchers concluded that radish is a cover crop worthy of further study for its potential to specifically control white grub pests while maintaining soil macrofauna diversity important for soil health. More research on different plant

1. White grubs, Scarabaeidae larvae
(Insecta, Coleoptera) Control by
plants in conservation agriculture:
effects on macrofauna diversity
Bodovololona Rabary,
Naudin K, Letourmy P, Mze Hassani
I, Randriamanantsoa R, Michellon
R, Rafarasoa L, Ratnadass A
1

2. Outline
• Context & Objective
– Uplands rice production and constraints
– White grubs diversity and impacts
– Soil biofunctioning and macrofauna functional
groups
– Hypothesis and Objective
• Experimental setup
– The study site and layouts
– Sampling methods
• Results and discussion
• Conclusion
2

3. Uplands rice production and
constraints
• Rice, staple crop and food in Madagascar,
• Grown on 1.3 million Ha, 29% are upland rice
• Production of upland rice varieties is steadily
increasing in Madagascar
• Rice farmers are encountering several
constraints of which:
– High crop damage/loss caused by rice diseases
and pests, including weeds.
– Most pest damages are caused by white grubs
3

4. Larva and adults of Madagascar’s
Scarabaeoidea (pests)
Heteroconus Heteronychus Heteronychus Apicencya
paradoxus bituberculatus arator rugifrons waterloti
MELOLONTHIDAE
DYNASTIDAE
(Randriamanantsoa et al., 2010)

5. White grubs damages
Attack at root or crown Attack might be as severe
levels according to species, as here
death of plant
The more efficient control method of white grubs is until
5
now ‘pesticides ‘

6. Larva of Madagascar’s Scarabaeoidea
(Non-pests)
Hexodon unicolor Bricoptis Euryiomia
unicolor variolosa argentea Serica sp.
DYNASTIDAE CETONIIDAE CETONIIDAE SERICIDAE
(Randriamanantsoa et al., 2010)
Some of them shows "soil engineering" behaviour 6

7. Soil biofunctioning and macrofauna
functional groups
• Promote nutrient cycling,
• Participate on soil organic matter dynamics, C
sequestration, emission of greenhouse gases
control
• Change the soil structure and water regime
• Encourage the growth and the health of the plants.
 build the quality and health of the soil over time
 Increase the quantity and the efficiency of plant
nutrients uptake
(Lavelle et al., 1997; Frouz et al. 2001; Hättenschwiler
& Gasser, 2005) 7

8. Major pathways for reducing the impact of
pests and diseases via plant species diversity
in agroecosystems (Ratnadass et al., 2011)
8

9. Hypothesis and Objective
Hypothesis: Increase in plant biodiversity + No-
tillage + cover crops  macrofauna diversity
 positive impact on pests.
Research question: If the plants have positive
impacts on pests, what are their effects on
macrofauna biodiversity (Non-target species)?
 Approach based on functional groups
diversity
9

10. Macrofauna’s food and nutrition
• Predators (other fauna)
• Phytophagous (plants)
• Saprophagous (decomposing organic matter)
• Detritiphagous (detritus)
• Xylophagous (wood-eating)
• Coprophagous (feces)
• Geophagous (soil)
 Functional groups

11. Characteristics
of the study
area
Antsirabe
Andranomanelatra
(19°46’ 45’’S, 47°06’ 25’’ E)
Central high plateau with high-
altitude tropical climate
Altitude: 1600 m.a.s.l.
Mean annual rainfall: 1450 mm
Ferrallitic clayey soil (clay
61.90 %, pH: 5,7)
More than 80 inhabitants / km²
11

12. Experimental field layout in 2009-
2010
A1 A2 A3 A4 B1 B2 B3
NB4
F1 F8
F2 F7
F3 F6
A8 A7 A6 A5 B8 B7 B6 B5
F4 F5
D1 D2 D3 D4 E1 E2 E3 E4 C1 C2 C3 C4
D8 D7 D6 D5 E8 E7 E6 E5 C8 C7 C6 C5
Sole Rice (NT)
NT = Direct seeding
Rice + Beans (NT)
CT = Conventional Tillage
Rice + Beans (CT)
Legend Rice + Vetch (NT)
Rice + Eleusine + Crotalaria (NT)
Rice + Cleome + Cosmos + Tagetes (NT)
Rice + Brachiaria (NT)
12
Rice + Radish (NT)

13. Plants used as cover
crops for controlling
White grubs
Fodder Radish (Raphanus sativus)
hairy vetch (Vicia villosa)
Cosmos caudatus
Cleome hirta Tagetes minuta
Brachiaria
mulato Crotalaria grahamiana
Eleusine coracana

14. Methods
• Modified TSBF : 1 monolith of
25 cm x 25 cm x 30 cm per plot
• Cut into litter and three layers:
0-10 cm, 10-20 cm, and 20-30
cm
14

15. Methods (cont’d)
• Hand sorting of invertebrates
> 2 mm
• Identification (taxa), counting
and weighing of Macrofauna.
Conservation in alcohol 70 °
• ANOVA of transformed data
for non-parametric tests.
15

16. Mean abundance of Macrofauna
within cropping systems
Macrofauna functional group
density (Individuals m-2) Non-Identified
1800
Saprophagous
1600
1400 Geophagous
1200
1000 Predators
800 Detritiphagous*
600
400 Phytophagous
200
0
16

17. Abundance of detritiphagous
within cropping systems
Detritiphagous density
(individuals m-2)
140 a
120 a a
a
100
80
a
60 a ab
40
20 b
0
17

18. Mean biomass of Macrofauna within
cropping systems
Macrofauna functional group biomass
25 (g m-2)
20 Non-Identified
15 Saprophagous
10 Geophagous
Predators
5
Detritiphagous
0
Phytophagous*
18

19. Phytophagous biomass within cropping systems
9 Phytophagous biomass (g m-2) a
8 a
7
6 a
5 a
4 a a
3
2
1 b ab
0
19

20. Conclusion & Perspectives
• Radish seems promising for phytophagous control.
• In addition, it did not reduce macrofauna diversity and abundance.
• Vetch was also favourable for macrofauna abundance but it did not
express white grub pest control potential.
• Our results emphasise the importance of studying a wide range of
plants as cover crops or residue mulch for soil pest control
Perspectives
• specific pest-suppressive effects of plants
• explore more plant species.
• Study the mechanisms involved
20

21. Thank you
21