Holotrichia oblita, H. parallela and Anomala corpulenta are important pests in the dry land areas of North China, which feed roots or stems of plants in larvae stage and leaves of variety of plants in adult stage. Most interestingly, three species all prefer to feeding on leaves of Ricinus communis, a non鄄host plant, despite that the extract of R. communis leaf is toxic to their larvae and adults. In order to elucidate the mechanisms behind this phenomenon, in the present study, the electroantennographic and behavioural responses of the male and female adults of three scarab beetle species to five components of R. communis leaf volatiles were tested using the electroantennogram ( EAG) and a Y鄄typed olfactometer, respectively. The EAG bioassay showed that the relative EAG values of three species male scarab beetles were higher to four components, i. e., dibutyl phthalate, cinnamaldehyde, 2鄄phenylethanol and benzyl alcohol, than that to control volatile ( Z) 鄄3鄄hexene鄄1鄄ol, especially the males of H. oblita exhibited strong responses to dibutyl phthalate and 2鄄phenylethanol, with 200.34% and 168.43% relative EAG values, respectively. Corresponding females of H. oblita responded strongly to cinnamaldehyde and dibutyl phthalate with the 146.01% and 135.12% relative EAG values, respectively. The relative EAG values of H. parallela to benzyl alcohol arrived 149.95%( male) and 167.86%( female) . A. corpulenta exhibited responses to dibutyl phthalate with about 144% the relative EAG values. The response of A. corpulenta male to benzyl alcohol is strong with the 143.70% relative EAG values. The results of behavioural bioassay indicated the preference to volatiles derived from http: / / www.ecologica.cn R. communisis is species鄄dependent, that is, H. oblita exhibited significant preferences to dibutyl phthalate and cinnamaldehyde, with the choice response percentages of 64% and 63% in females and 76% and 65% in males, significantly higher than that to ( Z) 鄄3鄄hexene鄄1鄄ol. Females and males of H. parallela showed significant preference to benzyl alcohol, with the 66% and 56% mean choice response percentages, respectively. A. corpulenta was most preferred to a green leaf volatile ( Z) 鄄3鄄hexene鄄1鄄ol, and the average choice response percentages of males and females to ( Z ) 鄄3鄄 hexene鄄1鄄ol were 88%, 87% and 89% in the controls of dibutyl phthalate, cinnamaldehyde and 2鄄phenylethanol, respectively. The results of comparison between R. communis volatiles and the female鄄produced sex pheromones of the tested scarab beetle species, found that R. communis leaves emitted abundant dibutyl phthalate, while the major components of H. oblita female鄄produced sex pheromone were glycine methyl ester and proline methyl ester, and the major component of H. parallela female鄄produced sex pheromone was methyl L鄄isoleucinate. Therefore, " sex pheromone misleading冶 may possibly answer for the preferences of two Holotrichia species to R. communis. The green leaf volatile ( Z ) 鄄3鄄hexene鄄1鄄ol may possibly be the main attractant of A. corpulenta to ...
