Canadian Forest Service Publications
Cross-order and cross phylum activity of Bacillus thuringiensis pesticidal proteins. 2013. van Frankenhuyzen, K. Journal of Invertebrate Pathology. 114:76-85.
Available from: Great Lakes Forestry Centre
Catalog ID: 34678
CFS Availability: PDF (request by e-mail)
The increasing number of Bacillus thuringiensis proteins with pesticidal activities across orders and phyla raises the question how widespread cross-activities are and if they are of sufficient biological significance to have implications for ecological safety of those proteins in pest control applications. Cross-activity is reported for 27 proteins and 69 taxa and is substantiated by reasonable evidence (mortality estimates) in 19 cases involving 45 taxa. Cross-activities occur in 13 primary rank families across three classes of pesticidal proteins (Cry, Cyt and Vip), and comprise 13 proteins affecting species across two orders, five pro teins affecting three orders and one protein affecting four orders, all within the class Insecta. Crossactivity was quantified (LC50 estimates) for 16 proteins and 25 taxa. Compared to toxicity ranges established for Diptera-, Coleoptera-, Lepidoptera- and Nematoda-active proteins, 13 cross-activities are in the low-toxicity range (10-1000 ug/ml), 12 in the medium - (0.10-10 ug/ml) and two in the high-toxicity range (0.01-0.10 ug/ml). Although cross-activities need to be viewed with caution until they are confirmed through independent testing, current evidence suggests that cross-activity of B. thuringiensis pesticidal proteins needs to be taken into consideration when designing and approving their use in pest control applications.
Plain Language Summary
Proteins produced by the bacterium Bacillus thuringiensis (Bt) are present in biopesticides that are used to combat forest insect pests in Canada, and in genetically modified (GM) crops that are cultivated all over the world. Regulatory approval and public acceptance of these pest management approaches hinge on the fact that toxicity of Bt proteins is usually confined to a narrow range of species within an insect order (e.g., beetles, flies or moths) that depends on the protein. Recent studies have revealed that some proteins can affect organisms outside their normal host range. This paper reviews published evidence of such activity and concludes that: (1) About 13% of the 148 Bt proteins tested to date affect organisms outside their normal host range, but such activity is limited to the class of insects (2) Nineteen proteins are known to affect species in two or more (up to four) insect orders (3) In about half of those cases, toxicity to species outside the normal host range is comparable to toxicity within. Most cross-activities have yet to be confirmed through independent testing, but the few that have been validated firmly establish the notion that Bt proteins are not as order-specific as was conventionally believed to be the case. This needs to be considered in the design and regulatory approval of their use for pest control.
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