Behavioural response of Colorado potato beetle (Leptinotarsa decemlineata) larvae to selected plant extracts

Potato leaves were treated with 2, 20 or 200g kg(-1) solutions of extracts of five plant species collected in Turkey, and then exposed to larvae of Colorado potato beetle, Leptinotarsa decemlineata (Say). During the first 24 h of exposure, leaf consumption was not affected by 2 g kg(-1) extracts, whereas significantly more leaf tissue remained on leaves treated with 20 g kg-1 extracts of Arctium lappa L., Bifora radians M Bieb, Humulus lupulus L. or Xanthium strumarium L. than on untreated control leaves. Feeding was not affected by the 20 g kg(-1) extract of Verbascum songaricum Schrenk ex Fisch & Mey. Extracts of an species at 200 g kg-1 reduced larval feeding, with H. lupulus and X. strumarium providing the greatest protection. Observations of larval behaviour over the first 15 min of exposure to these extracts revealed that the interaction of beetles with leaf tissue was significantly affected by plant extracts. Feeding frequency was not affected by 2 g kg(-1) extracts but was reduced by all higher concentrations. Feeding was inhibited completely by 20 g kg(-1) of H. lupulus extract and reduced significantly compared with the controls by all other extracts. Suppression of feeding was caused by all extracts at 200 g kg(-1), with V. songaricum providing 91% reduction in feeding duration. Rejection behaviour, in which larvae did not return to the leaf after their interaction with it, was rare on 2 g kg` extracts but seen in over 60% of larvae on 20g kg(-1) extracts and over 80% on 200g kg(-1) extracts. The present results demonstrate that these extracts have significant ability to protect potato leaves for up to 24 h by prevention of feeding behaviour by L. decemlineata. Further studies are needed to determine the potential of these plant extracts, or their active components, for use in biologically based pest management strategies. (c) 2006 Society of Chemical Industry.