Interactions between Cassava and Arthropod Pests

Study of the interactions between plants and arthropods and especially of the resistance of plants is an essential component of integrated pest management. In the context of interactions between cassava and its three main pests in Africa (cassava green mite, variegated grasshopper and cassava mealybug), it is observed that knowledge in this filed is not very advanced except for the cassava-mealybug model. The study of this began in 1987 and has revealed the following features: (i) the resistance to mealybug developed by cassava is partial and is expressed according to the three categories of resistance, i.e., non-preference, antibiosis and tolerance. The results indicate horizontal, polygenic resistance; (ii) the behavioural characteristic of the insect and the sensorial equipment of its antennae and labium (the site of olfactory and gustatory chemoreceptors) suggest that the chemistry of the surface of the plant probably plays a determinant role in the success of the plant recognition phase; (iii) cassava mealybug principally feeds on phloem sap of which the main component is sucrose and which has a low amino acids content, a high cyanide glycosides content and also contains glycosylated flavonoids including rutin. Comparison of cassava phloem sap and honeydew excreted by the insect indicates that all these compounds are ingested and metabolized; (iv) the strong positive correlation established between the degree of antibiotic resistance of various cassava genotypes and their phloem rutin contents suggests that this secondary compound contributes to plant resistance to the mealybug; (v) considerable fluctuations in the pest numbers observed each year in the field were linked with variations in phloem rutin contents and these variations are affected by cultural practices. It was concluded that; (i) research on plant-insect interactions is complex as it requires a multi-disciplinary approach involving entomologists, biochemist, plant physiologists and plant breeders; (ii) there is a need to develop such studies on the other cassava pests while deepening those on the cassava-mealybug model

Interactions between Cassava and Arthropod Pests

Study of the interactions between plants and arthropods and especially of the resistance of plants is an essential component of integrated pest management. In the context of interactions between cassava and its three main pests in Africa (cassava green mite, variegated grasshopper and cassava mealybug), it is observed that knowledge in this filed is not very advanced except for the cassava-mealybug model. The study of this began in 1987 and has revealed the following features: (i) the resistance to mealybug developed by cassava is partial and is expressed according to the three categories of resistance, i.e., non-preference, antibiosis and tolerance. The results indicate horizontal, polygenic resistance; (ii) the behavioural characteristic of the insect and the sensorial equipment of its antennae and labium (the site of olfactory and gustatory chemoreceptors) suggest that the chemistry of the surface of the plant probably plays a determinant role in the success of the plant recognition phase; (iii) cassava mealybug principally feeds on phloem sap of which the main component is sucrose and which has a low amino acids content, a high cyanide glycosides content and also contains glycosylated flavonoids including rutin. Comparison of cassava phloem sap and honeydew excreted by the insect indicates that all these compounds are ingested and metabolized; (iv) the strong positive correlation established between the degree of antibiotic resistance of various cassava genotypes and their phloem rutin contents suggests that this secondary compound contributes to plant resistance to the mealybug; (v) considerable fluctuations in the pest numbers observed each year in the field were linked with variations in phloem rutin contents and these variations are affected by cultural practices. It was concluded that; (i) research on plant-insect interactions is complex as it requires a multi-disciplinary approach involving entomologists, biochemist, plant physiologists and plant breeders; (ii) there is a need to develop such studies on the other cassava pests while deepening those on the cassava-mealybug model

Electrically recorded feeding behaviour of cassava mealybug on host and non-host plants.

Le comportement alimentaire de la cochenille du manioc (#Phenacoccus manihoti) a été étudié par électrographie de pénétration (EPG, analyse en courant continu) et par microscopie optique. Cette étude a permis de confirmer le caractère typiquement phloémophage de l'alimentation de cet Homoptère, présentant une large prédominance du trajet extracellulaire des stylets, comme cela est également observé chez les pucerons. Les similitudes des tracés EPG effectués sur cochenille et sur pucerons ou aleurodes ont permis d'adopter la même typologie du signal. Les principales différences avec les pucerons concernent le nombre moins important et la durée plus longue des ponctions intracellulaires (20 s en moyenne contre 5 à 7 s chez les pucerons), l'allongement du temps d'accès au phloème et une moins grande mobilité des stylets lors de la phase de recherche du phloème. La comparaison du comportement alimentaire sur 6 plantes, parmi lesquelles deux hôtes occasionnels (#Talinum et poinsettia), un hybride et trois variétés courantes de manioc (#Manihot esculenta), a permis de différencier plusieurs profils de pénétration. Les ponctions intracellulaires se sont révélées plus courtes sur hôtes occasionnels, qui induisent également, malgré la variabilité observée, un allongement net de la période de localisation du phloème et donc un retard à l'ingestion. Aucune des plantes testées ne contient d'alcaloïdes, et les composés cyanés se restreignent au genre #Manihot, hôte naturel de la cochenille. Les flavonoïdes totaux ne permettent pas de distinguer plantes hôtes et non-hôtes, à la différence des acides phénoliques. (Résumé d'auteur

Agroecological transformation for sustainable food systems : Insight on France-CGIAR research

This 26th dossier d’Agropolis is devoted to research and partnerships in agroecology. The French Commission for International Agricultural Research (CRAI) and Agropolis International, on behalf of CIRAD, INRAE and IRD and in partnership with CGIAR, has produced this new issue in the ‘Les dossiers d’Agropolis international’ series devoted to agroecology. This publication has been produced within the framework of the Action Plan signed by CGIAR and the French government on February 4th 2021 to strengthen French collaboration with CGIAR, where agroecology is highlighted as one of the three key priorities (alongside climate change, nutrition and food systems)