Possible role of plant and soil pH-redox status in the distribution and pestiferous potential of white grubs (Coleoptera: Scarabaeidae) associated with upland rice in Madagascar

Ratnadass Alain, Randriamanantsoa Richard, Rasoanaivo Lahatra, Husson Olivier, Delatte Hélène, Ravaomanarivo Lala Harivelo. 2024. Possible role of plant and soil pH-redox status in the distribution and pestiferous potential of white grubs (Coleoptera: Scarabaeidae) associated with upland rice in Madagascar. In : Climate Change Impacts on Insects and One Health: Book of Abstracts of the 25 th Biennial Scientific Conference. s.l. : AU-IASPC, Résumé, p. 53., 1 diaporama (13 vues) AAIS Scientific Conference. 25, Lusaka, Zambie, 18 Novembre 2024/22 Novembre 2024.

Résumé : In Madagascar Central Highlands, upland rice-associated white grub (WG: scarab beetle larvae) trophic plasticity ranges from obligatory herbivory to obligatory saprophagy, depending on species and soil organic matter (SOM) content. In 2005, at Andranomanelatra, we counted and identified all WGs in soil monoliths sampled downhill, at mid-slope, and uphill fields, along two topo-sequences. Primarily herbivorous Apicencya waterlotii and Heteronychus arator were dominant uphill and absent downhill with intermediate levels at mid-slope, while more plastic Heteronychus bituberculatus and Heteronychus plebeius showed the reverse trend, which was ascribed to differences in SOM. Since then, a conceptual framework has been developed, highlighting oxidation-reduction (redox potential: Eh) and acidification-alkalinization (pH) processes as key to the regulation of interactions between soil-plants and pests- pathogens systems. We, therefore, surveyed WGs in 2024 along two new topo-sequences and assessed Eh-pH in situ on rice grown near sampled soil monoliths, with a recently developed hand scanner using Near-Infrared Spectrometry and predictions based on regression algorithms combined with deep learning. We also identified all weeds in neighboring rice harvest quadrats. Facultative herbivorous Hyposerica sp. and Triodontus nitidulus WGs were dominant, respectively uphill and at mid-slope, but not downhill, and downhill and at mid-slope, but not uphill. Rice plants were more oxidized uphill and at mid-slope than downhill. Weed species bioindicators of reduced soils were found only downhill. Thus, WG damage could be managed by creating reducing conditions in soils, e.g., with conservation agriculture, which increases “reduced” (photosynthesis energy-rich) fresh SOM content, unlike till farming, which results in oxidation.

Mots-clés libres : Redox potential, White grubs, Upland rice, NIRS, Conservation agriculture

Auteurs et affiliations

• Ratnadass Alain, CIRAD-PERSYST-UPR AIDA (REU) ORCID: 0000-0002-8873-5671
• Randriamanantsoa Richard, FOFIFA (MDG)
• Rasoanaivo Lahatra, FOFIFA (MDG)
• Husson Olivier, CIRAD-PERSYST-UPR AIDA (FRA) ORCID: 0000-0001-9587-5819
• Delatte Hélène, CIRAD-BIOS-UMR PVBMT (REU)
• Ravaomanarivo Lala Harivelo, Université d'Antananarivo (MDG)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/611131/)

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