Host plant finding by Acraea acerata Hew. (Lepidoptera: Nymphalidae), the sweet potato butterfly : implications for pest management

• Main Author: Hitimana, Nicolas
• Published: University of Edinburgh 2001
• Subjects: 590
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.652475

Phytophagous insects such as lepidopteran species utilise both olfactory and visual cues to locate their host-plants used as mating or oviposition sites, shelter or food. Larvae of <i>Acraea acerata </i>feed on sweet potato plant leaves causing more that 50% loss of sweet potato tuber yield in some East African countries. Attempting to elaborate a management strategy to control <i>A. acerata </i>suitable to a tropical resource-poor farming system, it was essential to investigate how the butterfly finds its hosts-plants. The results of a wind tunnel bioassay using glass-screened, muslin-screened and non-screened sweet potato plants suggested that sweet potato plant volatiles play an important role in attracting <i>A. acerata </i>to its host-plant. This was supported by both the distance moved by female <i>A. acerata </i>towards muslin-screened plants (olfactory cues) and the percentage of butterflies which landed on the screen. Visual stimuli seemed to have a negative effect. The attractiveness of sweet potato plant volatiles to <i>A. acerata</i> was later confirmed by the use of volatiles collected by headspace entrainment from sweet potato plants. The main components of sweet potato plant volatiles were tentatively identified by GC-MS (Gas Chromatography coupled with Spectrometry) analysis and electrophysiological responses were recorded for some of them. Compared to ethylbenzene, 3-carene and (-) trans-caryophyllene, 3-hexen-1-ol,(Z), a general green leaf alcohol, elicited far more substantial EAG (electroantennogram) responses in <i>A. acerata.</i> This result suggested that <i>A. acerata</i> might well respond to a specific blend of volatiles made up of the different chemical components of sweet potato plant volatiles instead of one or two specific chemical components. Considering the important role of sweet potato plant volatiles in attracting <i>A. acerata, </i>a number of plants reported to be repellent to herbivorous insects were mixed with sweet potato plants and screened for repelling/disorienting of female <i>A. acerata</i> in olfactometer and wind tunnel bioassays.