We assessed the effects of transgenic potato lines with anti-cathepsin D activity on growth, development and digestive physiology of Colorado potato beetle (Leptinotarsa decemlineata Say) larvae. Transgenic lines expressing tomato cathepsin D inhibitor (CDI) were first developed, and selected based on their CDI content. Lines expressing varying levels of CDI were then provided to 3rd-instars for 132 h, with the aim of measuring different parameters including leaf consumption, relative growth rate, time for molting and digestive proteinase activities. Consumption of leaf material during the first 12-24 h was slightly affected for larvae provided with the transgenic lines, the most visible effects being observed for the clones with high transgene activity. Growth rate and time for molting were also slightly affected after 12-24 h, but relative growth rates after 132 h were similar for all the transgenic clones. In contrast, cathepsin D activity was drastically decreased in larvae fed high levels of CDI for 24 h, but increased with time to reach levels similar to those noted for control insects. Noteworthy, the importance of cysteine (and serine) proteinases increased in CDI-fed larvae, suggesting compensation in the insect based on both the overexpression of cathepsin D-like proteinases, and the production of proteinases from other classes. Overall, these observations point out the ability of potato beetles to modulate their digestive proteases in response to aspartate-type inhibitors in the diet. They also show the importance of devising improved strategies for the effective inhibition of insect digestive proteinases, based for instance on the expression in potato of chimeric, hybrid inhibitors active against proteinases from different classes.
Species 1: Coleoptera Chrysomelidae Leptinotarsa decemlineata (Colorado potato beetle)
Keywords: proteinase inhibitors, digestive cathepsin D
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