Orientation of Colorado potato beetle to natural and synthetic blends of volatiles emitted by potato plants Joseph C. Dickens USDA-ARS, Beltsville Agricultural Research Center, Plant Sciences Institute, Vegetable Laboratory, Bldg. 010A, Room 240, 10300 Baltimore Avenue, Beltsville, MD 20705, U.S.A. Abstract 1 Behavioural responses of the Colorado potato beetle (CPB), Leptinotarsa decem- lineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from solanaceous host plants (potato and tomato), a non-host legume (soybean), and 13 synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays. 2 Both male and female CPB were attracted to volatiles emitted by mechanically damaged potato foliage, but not to mechanically damaged tomato foliage; CPB offered a choice between the two damaged solanaceous plants did not show a preference. 3 Among 16 odourous blends or individual chemical components of potato plant emissions tested, six blends were attractive, two were repellent, and eight elicited no preference in laboratory bioassays. Volatile blends containing relatively high amounts of the green leaf volatiles (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol, or the sesquiterpene b- caryophyllene, were unattractive or repellent. Minimal blends at- tractive to CPB were comprised of (Z)-3-hexenyl acetate (6)-linalool and methyl salicylate: the combination of all three chemicals elicited sexually dimorphic at- traction of males; two component blends comprised of (Z)-3-hexenyl acetate and either (6)-linalool and methyl salicylate attracted both sexes. Individual com- pounds were inactive. No signi®cant difference was noted between two attractive blends, or an attractive synthetic blend vs. mechanically damaged potato foliage. 4 These results show that CPB are attracted to blends of speci®c chemicals emitted by their host plants and provide a basis for the use of plant attractants as a com- ponent of integrated management of pestiferous populations. Keywords Behaviour, chemical blends, Chrysomelidae, insect/host plant, Leptino- tarsa decemlineata, plant attractant, potato, Solanum tuberosum. Introduction The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say)(Coleoptera:Chrysomelidae),isoneofthemostdamaging insect pests of potatoes (Solanum tuberosum L.). Since it was ®rst noted as a pest of potatoes in 1859, CPB has developed resistancetonumerouschemicalsthathavebeenappliedforits control (Casagrande, 1987). Alternatives to pesticides, e.g. biocontrolagentsandhostplantresistance,havehadpromising results and may enhance programmes aimed at integrated pest management. Behavioural chemicals such as pheromones and plantattractantscouldalsobeusefulbothinsurveyandcontrol ofCPB(Dickens,1999). OrientationofCPBtoconspeci®csanditshostplanthasbeen investigatedintensively.Althoughseveralstudieshavedemon- strated the presence of a contact pheromone involved in CPB mating on the elytra of females (Jermy & Butt, 1991; Otto, 1996),proofofasexpheromonethatisactiveoveradistancehas beenmoreelusive(DeWilde etal.,1969;Levinson etal.,1979; Edwards & Seabrook, 1997). McIndoo (1926) devised an olfactometerthatshowedtheattractivenessofvolatilesemitted by potato plants to CPB adults; the ®rst demonstration that volatile emissions by plants attract insects. Although various other investigators veri®ed McIndoo's initial observation (McIndoo, 1926; Schanz, 1953; DeWilde etal., 1969; Visser, Correspondence: Dr J. C. Dickens. Tel: +1 301504 8957; fax: +1 301504 5555; e-mail: jdickens@asrr.arsusda.gov ã 2000 Blackwell Science Ltd Agricultural and Forest Entomology (2000) 2, 167±172 Agricultural and Forest Entomology (2000) 2, 167±172