Th2_Larvae of Scarabeoidea (called white grubs) can be beneficial to rice growth: case study on Hexodon unicolor unicolor (Dynastidae) on the Highlands of Madagascar
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Th2_Larvae of Scarabeoidea (called white grubs) can be beneficial to rice growth: case study on Hexodon unicolor unicolor (Dynastidae) on the Highlands of Madagascar

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3rd Africa Rice Congress ...

3rd Africa Rice Congress
Theme 2: Intensification and diversification
Mini symposium: Rice pests: evidence of effects and management
Author: Radriamanantsoa

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  • 1. 1 Larvae of Scarabeoidea (called white grubs) can be beneficial to rice growth: case study on Hexodon unicolor unicolor (Dynastidae) on the Highlands of Madagascar Randriamanantsoa R., Raharinindrina S., Rabary B.; Blanchart E., Quaranta B.; Naudin K.., Ratnadass A., Rafamatanantsoa E. ; Rakotosolofo H. 1
  • 2. 2 WHITE GRUBS IN UPLAND RICE CROPS IN MADAGASCAR Taxonomic and functional diversity White grubs= main pests on upland crops
  • 3. 3 Damages Crown dilaceration Main families causing damages on upland rice: Dynastidae and Melolonthidae Root attack
  • 4. 4 Rhizophagous : Apycencya waterlotii White grubs feeding diet Saprophagous: Euryiomia argentea Facultative rhizophagous: Heteroconus paradoxus
  • 5. 5 Case study: Hexodon unicolor unicolor acting as a soil engineer Abundance in rice crops PITFALL TRAPS Rice-based agrosystems with: Brachiaria mulato, Crotalaria grahamiana; Raphanus sativus; no mulch Behaviour and rice growth Residues of different types: Brachiaria mulato, Crotalaria grahamiana; Raphanus sativus; no mulch
  • 6. 6 Mean of adults density/m2 80 RESULT S 70 60 Brachiaria mulato 50 40 Crotalaria grahamiana 30 Raphanus sativus 20 No residu 10 Abundance of H. unicolor unicolor in different systems 0 June August Dates of observation Adult =omnivorous, present in fields only during the rainy season Mean of larval density/m2 March 80 70 60 50 Brachiaria 40 Crotalaire 30 Population of larvae 20 depending on the season 10 Low density in systems with 0 Raphanus sativus et Crotalaria grahamiana Radis fourrager Sans résidus Mars Juin Sampling Août
  • 7. 7 Burrowing activity Burrow opening Residues of Stylosanthes guianensis Incorporation of residues in the soil Residues of Soya bean
  • 8. 8 Effect of residue types on the mortality of H. unicolor larvae Larval mortalty rate 100 80 60 40 20 0 Cow dung Maize No residu Soya bean Stylosanthès guianensis Types of residu The mortality of H. unicolor unicolor larvae is higher in the absence of residues and lower for legumes residues
  • 9. 9 35 d 30 d cd bcd bcdbcd Indirect effects of H. unicolor larvae on rice growth in systems with dead mulches 25 (cm) abc ab a 20 a Rice growth higher with soya and stylosanthes residues or with cow manure than with maize residues or absence of residues, irrespective of the presence of larvae 15 10 5 0 R RH RM RMH RJ RJH RS RSH RF RFH Treatments RF= rice+cow dung; RFH= rice+cow dung+larva ; RJ= rice+soya residu; RJH= rice+soya residu +larva; RM= rice+maize; RMH= rice+maize residu+larva ; RR= rice; RRH= rice + larva;; RS= rice+stylosanthes residu; RSH= rice+stylosanthes residu +larva ; Légumes residues and cow manure much more decomposed by larvae
  • 10. 10 CONCLUSIONS Not all Scarabeoidea larvae are harmful for plants Viability of larvae depends on the presence/absence and th type of organic matter (residues or manure) Larvae could have beneficial functions for soil and plants by incorporating and regulating the mineralisation of soil organic matter.
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