Dry bean volatile organic compounds mediating host choice in Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae)

Abstract

SummaryTwo-choice tests were conducted on five bean cultivars of Phaseolus vulgaris L. and one of Vigna unguiculata (Walp.) to evaluate the attractiveness for mated males and females of a worldwide granary pest, Acanthoscelides obtectus Say. Attraction behaviour was studied under choice conditions in a static air and dynamic airflow olfactometer on red, white and cowpea cultivars against control beans. Behavioural differences between males and females were recorded. In the static atmosphere test, males were more attracted than females to dry beans, especially red and white cultivars; whereas cowpea beans attracted fewer females. Yellow and brown beans were attractive to males but were not significantly different from control beans. A dynamic air olfactometer experiment gave different results. The best responsiveness of females was when stimulated by red and control cultivar beans. They were not attracted by cowpea beans. Volatile organic compounds (VOCs), released from red, cowpea and control beans, were tentatively identified from solid phase microextraction (SPME) collections and headspace gas chromatography coupled to mass spectrometry (HS-GCMS). Analysis revealed a presence of 33 and 32 VOCs respectively in control and cowpea beans and 29 in red beans. VOC blends, released by studied cultivars, were mainly composed of terpenic compounds with a specific ratio for each cultivar. A comparison of linalool/limonene ratios for each cultivar suggests emission of specific chemical signals in control and red beans, whereas in cowpea beans the ratio of linalool and limonene was reversed and associated with a high level of pentanal. Qualitative and quantitative differences in the blend composition of red, cowpea and control beans may explain the choice behaviour of the bruchid, which is discussed in a biological and behavioural context.