Bodovololona Rabary,

Naudin K, Letourmy P, Mze Hassani I, Randriamanantsoa R, Michellon

R, Rafarasoa L, Ratnadass A

White grubs, Scarabaeidae larvae

(Insecta, Coleoptera) Control by

plants in conservation agriculture:

effects on macrofauna diversity

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• 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

Outline

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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

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Larva and adults of Madagascar’sScarabaeoidea (pests)

Heteroconusparadoxus

Heteronychusbituberculatus

Heteronychusarator rugifrons

Apicencyawaterloti

MELOLONTHIDAE

DYNASTIDAE

(Randriamanantsoa et al., 2010)

White grubs damages

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Attack at root or crown levels according to species, death of plant

Attack might be as severe as here

The more efficient control method of white grubs is until now ‘pesticides ‘

Larva of Madagascar’s Scarabaeoidea(Non-pests)

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Hexodon unicolorunicolor

Bricoptisvariolosa Serica sp.

Euryiomiaargentea

SERICIDAEDYNASTIDAE CETONIIDAE CETONIIDAE

(Randriamanantsoa et al., 2010)

Some of them shows "soil engineering" behaviour

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

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(Lavelle et al., 1997; Frouz et al. 2001; Hättenschwiler& Gasser, 2005)

Major pathways for reducing the impact of

pests and diseases via plant species diversity

in agroecosystems (Ratnadass et al., 2011)

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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

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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

Characteristics

of the study

area

AntsirabeAndranomanelatra

Altitude: 1600 m.a.s.l.

Mean annual rainfall: 1450 mm

Central high plateau with high-

altitude tropical climate

Ferrallitic clayey soil (clay

61.90 %, pH: 5,7)

(19°46’ 45’’S, 47°06’ 25’’ E)

More than 80 inhabitants / km²

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F1 F8

F2 F7

F3 F6

F4 F5

C1 C2 C3 C4

C8 C7 C6 C5

A1 A2 A3 A4 B1 B2 B3 B4

A8 A7 A6 A5 B8 B7 B6 B5

D1 D2 D3 D4 E1 E2 E3 E4

D8 D7 D6 D5 E8 E7 E6 E5

N

Sole Rice (NT)

Rice + Beans (NT)

Rice + Beans (CT)

Rice + Vetch (NT)

Rice + Eleusine + Crotalaria (NT)

Rice + Cleome + Cosmos + Tagetes (NT)

Rice + Brachiaria (NT)

Rice + Radish (NT)

Legend

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Experimental field layout in 2009-

2010

NT = Direct seedingCT = Conventional Tillage

hairy vetch (Vicia villosa)

Brachiariamulato Crotalaria grahamiana

Cleome hirta Tagetes minuta

Cosmos caudatus

Fodder Radish (Raphanus sativus)

Plants used as cover

crops for controlling

White grubs

Eleusine coracana

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

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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.

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0200400600800

10001200140016001800

Macrofauna functional group density (Individuals m-2) Non-Identified

Saprophagous

Geophagous

Predators

Detritiphagous*

Phytophagous

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Mean abundance of Macrofauna

within cropping systems

17

0

20

40

60

80

100

120

140

Detritiphagous density (individuals m-2)

aa

a

b

a

ab

aa

Abundance of detritiphagous

within cropping systems

18

0

5

10

15

20

25

Macrofauna functional group biomass(g m-2)

Non-Identified

Saprophagous

Geophagous

Predators

Detritiphagous

Phytophagous*

Mean biomass of Macrofauna within

cropping systems

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0123456789 Phytophagous biomass (g m-2)

b

a

a

a

a

a

ab

a

Phytophagous biomass within cropping systems

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

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Thank you