Volatiles emitted by male and female T. infestans before and during copula were collected on Porapak-Q filters, desorbed with dichloromethane, and analyzed by gas chromotography and gas chromatography-mass spectrometry after confirmation of attractiveness in an arena bioassay. Chemical analysis confirmed the presence of (R,S)-2- and 3-methylbutan-1-ol in a 2:1 ratio; short chain acids (ethanoic to nonanoic acid); long chain acids decanoic to (Z)-9-octadecenoic acid; aliphatic aldehydes (hexanal to nonanal), benzaldehyde and dipropylsulphide from insects in copula. Electroantennographic studies conducted with a homologous series of aliphatic aldehydes on female and male T. infestans showed that, for a given dose, EAG responses elicited from both sexes increased with increased chain length up to nonanal, after which EAG-activity declined. Attractiveness of non-acidic trace components identified in the volatiles were tested on male and female T. infestans, in an arena bioassay using a video tracking method. Aliphatic C6 to C10 aldehydes were tested: hexanal (1–100 μg) and heptanal (10 μg) were attractive to female T. infestans, high doses of octanal and nonanal (1–100 μg) were unattractive to male and female T. infestans but low doses of nonanal (0.01–0.1 μg) were attractive to male T. infestans. Benzaldehyde was highly attractive to female T. infestans at low doses (0.05–0.1 μg). 3-methylbutan-1-ol was attractive to male T. infestans at high dose (1,000 μg). (S) or (S,R) 2-methyl-butan-1-ol were anattractive to males or females (1–1,000 μg). Blends of hexanal and benzaldehyde (20:1 and 40:1) showed an additive effect on attraction compared with hexanal alone, when tested on female T. infestans. The study has demonstrated the presence of a number of electrophysiologically and behaviorally active compounds in volatiles emitted by T. infestans in copula that may have a role in the postulated copulation pheromone.
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Vol. 39 • No. 1