Patrick Turpin

Resistance to Melanaphis sacchari in the sugarcane cultivar R 365

This study focuses on the resistance of sugarcane, Saccharum spec. (Poaceae), to the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), which vectors Sugarcane yellow leaf virus (SCYLV). Resistance was characterized in cultivar R 365, using a 3‐year field trial and laboratory experiments on potted plantlets and excised leaves. R 365 reduced aphid populations in the field by antixenosis and antibiosis. Using the electrical penetration graph technique, we detected delayed aphid salivation in phloem and inhibition of passive phloem sap uptake in R 365. The resistance factors also proved to be effective against the corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae), another vector of SCYLV.

Genetic diversity and differentiation among insular honey bee populations in the southwest Indian Ocean likely reflect old geographical isolation and modern introductions

With globalization the Western honey bee has become a nearly cosmopolitan species, but it was originally restricted to the Old World. This renowned model of biodiversity has diverged into five evolutionary lineages and several geographic “subspecies.” If Apis mellifera unicolor is indubitably an African subspecies endemic to Madagascar, its relationship with honey bees from three archipelagos in the southwest Indian Ocean (SWIO) hotspot of biodiversity is misunderstood. We compared recent mtDNA diversity data to an original characterization of the nuclear diversity from honey bees in the Mascarenes and Comoros archipelagos, using 14 microsatellites, but also additional mtDNA tRNALeu-cox2 analysis. Our sampling offers the most comprehensive dataset for the SWIO populations with a total of 3,270 colonies from 10 islands compared with 855 samples from Madagascar, 113 from Africa, and 138 from Europe. Comprehensive mitochondrial screening confirmed that honey bees from La Réunion, Mauritius, and Comoros archipelagos are mainly of African origin (88.1% out of 2,746 colonies) and that coexistence with European lineages occurs only in the Mascarenes. PCA, Bayesian, and genetic differentiation analysis showed that African colonies are not significantly distinct on each island, but have diversified among islands and archipelagos. FST levels progressively decreased in significance from European and African continental populations, to SWIO insular and continental populations, and finally among islands from the same archipelago. Among African populations, Madagascar shared a nuclear background with and was most closely related to SWIO island populations (except Rodrigues). Only Mauritius Island presented clear cytoplasmic disequilibrium and genetic structure characteristic of an admixed population undergoing hybridization, in this case, between A. m. unicolor and A. m. ligustica, A. m. carnica and A. m. mellifera-like individuals. Finally, global genetic clustering analysis helped to better depict the colonization and introduction pattern of honey bee populations in these archipelagos.