Electrophysiological responses of the lepidopterous stemborers Chilo partellus and Busseola fusca to volatiles from wild and cultivated host plants.

The stemborers Chilo partellus and Busseola fusca are major pests of subsistence cereal farming in Africa. Volatiles released by two cultivated hosts, sorghum and maize (Sorghum bicolor and Zea mays), and two wild grass hosts, Pennisetum purpureum and Hyparrhenia tamba, were collected by air entrainment. Electrophysiologically active components in these samples were detected by coupled gas chromatography-electroantennography (GC-EAG), and the active peaks identified by gas chromatography-mass spectrometry. A total of 41 compounds were identified from the four plant species, all of which, as well as two unidentified compounds, elicited an electrophysiological response from one or both of the stemborers. The compounds included a number of green leaf volatiles and other aliphatic aldehydes, ketones, and esters, mono- and sesquiterpenoids, and some aromatic compounds. EAG studies with authentic samples, conducted at two discriminating doses for all compounds, and dose-response curves for 14 of the most highly EAG-active compounds, showed significant differences in relative responses between species. The compounds that elicited large responses in both species of moths included linalool, acetophenone, and 4-allylanisole, while a number of compounds such as the aliphatic aldehydes octanal, nonanal, and decanal elicited a large response in B. fusca, but a significantly smaller response in C. partellus. Furthermore, the wild hosts produced higher levels of physiologically active compounds compared with either of the cultivated hosts. These differences are discussed in relation to the differential attraction/oviposition of the two stemborers observed in the field and, particularly for eastern African small-scale farming systems, in the context of using a push-pull strategy for their control.

Diel periodicity in the production of green leaf volatiles by wild and cultivated host plants of stemborer moths, Chilo partellus and Busseola fusca.

The volatile chemicals produced by four poaceous plant species, blue thatching grass, Hyparrhenia tamba, Napier grass, Pennisetum purpureum, sorghum, Sorghum bicolor, and maize, Zea mays, which are host plants for the lepidopterous stemborers, Chilo partellus and Busseola fusca, were collected by air entrainment and analyzed by gas chromatography. The total quantities of volatiles collected hourly, over a 9-hr period, from P. purpureum and H. tamba showed an approximately hundredfold increase in the first hour of the scotophase. Thereafter, the amount decreased rapidly to levels present during photophase. Although onset of scotophase also triggered an increase in quantities of volatiles collected from two cultivars of S. bicolor and two out of three cultivars of Z. mays, these increases were less dramatic than in the two wild grasses, being only up to 10 times as much as in the last hour of photophase. Analysis showed that up to 95% of the increase in volatiles at the onset of the scotophase was due to just four compounds, the green leaf volatiles hexanal, (E)-2-hexenal, (Z)-3-hexen-1-ol, and (Z)-3-hexen-1-yl acetate, with the latter dominating the volatile profile. Volatiles from P. purpureum were also collected at 10-min intervals for 70 min spanning the transition from light to dark. The vast increase in production of the green leaf volatiles in this species occurs in the first 10 min of the scotophase followed by a rapid decline within the next 20 min. The relevance of these results to the control of stemborers in a "push-pull" strategy is discussed.