Control of the grapevine moth Lobesia botrana through genetic engineering manipulation of host-plant volatiles
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The European grapevine moth, Lobesia botrana, is one of the most important pests of grape. Feeding activity by caterpillars leads to direct damage to reproductive plant tissues (flower buds and berries), and also to indirect damage by promoting secondary infections by microorganisms. Current control systems are based either on the use of insecticides or on mating disruption: while the first is not environmentally friendly, the second is not particularly suitable for non-delimited areas or areas where the pest population is high. Previous studies have shown that a synthetic blend of the three terpenoids (E)-β-caryophyllene, (E)-β-farnesene and (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) was as attractive for the moth as the complete grape odour profile under laboratory conditions. The same studies also showed that the specific ratio of these compounds in the grape bouquet was crucial, because small variations in the proportion of any of the three volatiles resulted in almost complete inhibition of the blend’s attractiveness. Here, we report on the creation of stable grapevine transgenic lines with modified (E)-β-caryophyllene and (E)-β-farnesene emission and thus with an altered ratio compared with the original plants. When headspace collections from these plants were tested in wind-tunnel behavioural assays, they were less attractive than control extracts. This result was confirmed by testing synthetic blends that imitated the ratios found in natural and transformed plants, as well as by testing the plants themselves. With this evidence, we suggest that a strategy based on volatile ratio modification may also interfere with the host-finding behaviour of L. botrana in the field, paving the way for new pest-control methods.