From population to species: morphological and molecular diversity in east African stem borer species of the genus Manga Bowden 1956 (Lepidoptera: Noctuidae)

Abstract

Larvae of noctuid stem borers were collected from wild monocot plants in Eastern Africa, from Ethiopia to Mozambique, and reared to the adult stage. Three species of the African genus Manga Bowden 1956 (Lepidoptera: Noctuidae) were found, all restricted to host plants of the family Poaceae. M. melanodonta (Hampson) was collected in stems of Panicum maximum Jacquin, Setaria megaphylla (Steudel) Th. Durand & Schinz and Setaria plicatilis (Hochstetter) Engler; M. nubifera (Hampson) stat. rev., and M. fuliginosa n. sp., were both found only in stems of P. maximum. The second species was in the past sunk with M. melanodonta as a synonym, but the present study shows its validity. Descriptions are given of the new species as well as of features not yet described of known species (female habitus and male and female genitalia of M. melanodonta and M. nubifera) and of the intraspecific morphological variation observed in the male genitalia. Larval morphology and life habits are described. Pictures of the adults and genitalia of the other species of the genus are provided except for M. bisignata Laporte that is sunk with Busseola quadrata Bowden as a synonym (n. syn.). The molecular diversity of the collected species was studied using the mitochondrial gene Cytochrome b. A complex history of successive fragmentation events was revealed. The combination of three forces appeared to have shaped this diversity: the main paleo-climatic events (successive dry and humid periods), the geological barriers, particularly the Rift Valley, and specialization on new host plants. A molecular clock proved to be acceptable for all clades except for the species that first diverged, Manga fuliginosa. The dates of the major paleo-climatic events of the last 5 million years appeared to correspond to the observed divergence events when using an evolutionary rate of 1.15% per million years, with a correction for M. fuliginosa. Isolation by the Rift Valley favoured diversification in some instances, and the adaptation of Manga melanodonta to new host plants enabled the colonization of humid environments. A scenario for the evolution of the group is proposed, from its origin in Austral Africa about 5 million years ago and its northward expansion, until the recent migrations of Manga nubifera during the past million years.