Insecticidal activity of avidin and streptavidin against four species of pest Lepidoptera

Abstract

AbstractTwo biotin‐binding proteins, avidin and streptavidin, were found to be insecticidal to the larvae of four species of Lepidoptera – light brown apple moth, Epiphyas postvittana (Walker) (fam. Tortricidae), green‐headed leaf‐roller, Planotortrix octo (Dugdale) (fam. Tortricidae), brown‐headed leaf‐roller, Ctenopseustis obliquana (Walker) (fam. Tortricidae) and potato tuber moth, Phthorimaea operculella (Zeller) (fam. Gelechiidae). Mortality occurred in all species, but there was a wide range in susceptibility. P. operculella larvae were the most susceptible with an LC50 of respectively, 2.3 μg ml−1 for avidin and 1.4 μg ml−1 for streptavidin after 9 days. E. postvittana larvae had an LC50 of 43.4 μg ml−1 for avidin after 21 days, and C. obliquana larvae of 45.7 μg ml−1 for avidin after 28 days. Although significant mortality occurred in P.octo at the highest doses of avidin, there was no sufficient dose‐mortality response to calculate an LC50 for this species. For all species mortality curves were steep over a close range of doses followed by a plateau where mortality did not increase significantly with dose and did not reach 100%. Mortality was significantly affected by the amount of biotin in the diet on which the parental generation had been reared. Where this was rich in biotin, significant mortality of the offspring was much lower: larval offspring of a colony of E. postvittana, reared for five generations on a biotin‐free diet had an LC50 of 5.1 μg ml−1 after 14 days compared with 76.7 μg ml−1 for larvae from a colony reared on general purpose diet. The implications for use of these proteins to confer insect resistance on transgenic plants are discussed.