Cry3

Cry3 refers to a group of crystal (Cry) toxins produced by the bacterium Bacillus thuringiensis. Cry3 proteins are classified within the Bt Cry toxin family and are active primarily against beetle pests (order Coleoptera). They are produced as inactive protoxins during spore formation and are activated in the insect gut by proteolytic enzymes, after which they exert insecticidal effects.

Mechanism and structure: Cry3 toxins are delta-endotoxins that typically require proteolytic processing in the insect midgut to become activated. The active toxin binds to receptors on midgut epithelial cells and forms pores, causing cell lysis, gut dysfunction, and ultimately insect death. This mode of action is relatively specific to certain beetle species, contributing to selectivity in pest control.

Target pests and use: The Cry3 family is primarily directed at coleopteran pests, especially beetles such as corn rootworms, which feed on plant roots and can cause significant agricultural damage. Cry3 toxins are used in two main ways: as microbial Bt sprays and, more prominently, in transgenic crops engineered to express Cry3 proteins. In crops like maize, Cry3 variants have been deployed to reduce rootworm populations, often in combination with other Bt toxins or agronomic practices.

Resistance management and regulation: Field populations can develop resistance to single-toxin Cry3 proteins, prompting integrated pest management strategies that include refuge planting and toxin pyramiding with additional Bt proteins. Bt-derived Cry toxins, including Cry3, have undergone regulatory evaluation for environmental and human safety before commercial use.

History: Cry3 toxins were identified and developed within the Bt toxin framework during the late 20th century and have been implemented in commercial Bt crops since the 1990s, contributing to beetle pest management in agriculture.