Hi all
I received a couple of messages re: Bt crop protection. It was not my intention to get deep into the topic, but rather to point out that it's been around a long time, and is a complex subject. It has been further complicated by its inclusion in transgenic crops. And sadly, it appears prone to the same pitfalls as other chemical crop controls -- pests develop resistance to it. 
PLB

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> The discovery of Bacillus thuringiensis (Bt) toxins with effective insecticidal activity against pests and the development of transgenic technology of plants opened a new era of pest control. Transgenic Bt crops, including maize, cotton and soya bean, have now been produced and commercialized to protect against about 30 major coleopteran and lepidopteran pests, greatly benefiting the environment and the economy. 

> However, with the long-term cultivation of Bt crops, some target pests have gradually developed resistance. Numerous studies have indicated that mutations in genes for toxins activation, toxin-binding and insect immunization are important sources in Bt resistance. An in-depth exploration of the corresponding Bt-resistance mechanisms will aid in the design of new strategies to prevent and control pests. Future research will focus on Bt crops expressing new genes and multiple genes to control a broader range of pests as part of an integrated pest management programme.

Xiao Y, Wu K. 2019 Recent progress on the interaction between insects and Bacillus thuringiensis crops. Phil. Trans. R. Soc. B 374: 20180316. http://dx.doi.org/10.1098/rstb.2018.0316

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