title: Steroidal glycoalkaloids: chemical defence of edible African nightshades against the tomato red spider mite, Tetranychus evansi (Acari: Tetranychidae).
abstract: BACKGROUND
  Tetranychus evansi is an invasive pest of solanaceous crops in Africa, and in the field it differentially attacks edible African nightshades. The chemical basis for the differential attack on these plant species is largely unknown. Using bioassays and chemical analysis, we investigated the differential bioactivity of leaf extracts of three edible African nightshade species, Solanum sarrachoides, S. scabrum and S. villosum, on adult T. evansi females.
  
  
  RESULTS
  Only the bioactivity of the leaf extract of S. sarrachoides (LC50 7.44 mg mL(-1)) and that of its most polar fraction (LC50 5.44 mg mL(-1)) paralleled that of the positive control, neem oil (LC50 1.89 mg mL(-1)), across all doses tested. Liquid chromatography-quadruple time of flight-mass spectrometry identified a mixture of steroidal glycoalkaloids (SGAs), including α-solasonine, α-solamargine and derivatives of tomatine and demissine, which were neither detected in the crude extract nor in any of the fractions obtained from S. scabrum and S. villosum.
  
  
  CONCLUSIONS
  Our results suggest that the presence of SGAs may play a key role in the differential defence of edible African nightshades against attack by T. evansi. These findings may add to the plethora of environmentally friendly tools from natural plant products for management of T. evansi.
authors: Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, Nairobi, Kenya.|Department of Horticulture, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya.
authors: Juma J
authors: JJ
authors: Jared
authors: Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, Nairobi, Kenya.|Department of Horticulture, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya.
authors: Lucy K
authors: LK
authors: Murungi
authors: Department of Horticulture, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya.
authors: John
authors: J
authors: Wesonga
authors: Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, Nairobi, Kenya.
authors: Baldwyn
authors: B
authors: Torto
mesh_terms: D000470:Alkaloids / Q000737:chemistry* / Q000494:pharmacology*; D000818:Animals; D005260:Female; D010936:Plant Extracts / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry; D032322:Solanum / Q000737:chemistry* / Q000502:physiology; D013256:Steroids / Q000737:chemistry*; D040102:Tetranychidae / Q000187:drug effects* / Q000502:physiology
chemical_list: D000470:Alkaloids; D010936:Plant Extracts; D013256:Steroids
keywords: Solanum sarrachoides; Tetranychus evansi; bioactivity; glycoalkaloids