Antifeedant effects of several plant extracts on Colorado potato beetle larvae

The antifeedant activities of methanolic extracts made from seven plant species (Abutilon theophrasti Medic., Ajuga chamaepitys (L.) Schreb., Amorpha fruticosa L., Matricaria chamomilla L., Matricaria inodora L., Tanacetum vulgare L. and Tilia cordata Mill.) were assessed in the laboratory at 0.5% and 5% dosages against Colorado potato beetle (Leptinotarsa decemlineata Say) larvae. Three h and 24 h dual-choice and 3 h no-choice feeding bioassays were carried out with potato (Solanum tuberosum L.) leaf discs. Furthermore, during the no-choice test direct observations on larval behaviour were performed to help to distinguish the mode of action which underlies inhibition of feeding. At a dosage of 0.5% no plant extract deterred feeding of larvae. At 5% Matricaria inodora (and our standard Ajuga chamaepitys with well-known antifeedant properties) was the most potent antifeedant of the seven extracts tested. Antifeedant indexes and results of the behavioural observations suggest that M. inodora acts as a sensory mediated feeding deterrent, rather than as a toxin