Comparative utilisation of exotic and native Solanum (Solanaceae) species by Chnootriba hirta (Thunberg) (Coccinelidae), a native herbivorous ladybird
Résumé
Chnootriba hirta (Thunberg) feeds on the foliage of several native Solanum species in South Africa, with occasional associations with introduced congeners. In comparing the beetle’s performance and preferences across three exotic and one native Solanum species, this study produced an unusual result. During adult and larval no-choice tests, the exotic Solanum americanum Miller proved the most suitable host plant, followed by the native S. dasyphyllum Schumacher and Thonning, with the exotic cultivated S. lycopersicum Linnaeus (tomato) proving marginally suitable. In contrast, the exotic S. viarum Dunal, an invasive weed in the southern USA, did not support feeding and development. During adult choice tests, C. hirta did not discriminate between S. americanum and S. dasyphyllum, but avoided S. lycopersicum. These differences in host-plant suitability may relate, in part, to the presence of glandular leaf trichomes, renowned anti-herbivore defences, on S. viarum and S. lycopersicum, but not on S. americanum or S. dasyphyllum. Since C. hirta, a broadly oligophagous herbivore within the native Solanum insect community, cannot exploit S. viarum, the plant may well expand its range in South Africa due to an escape from insect herbivory.
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