Cry I toxins are effective mainly against:
Phylogenetic analysis of Cry toxin specificity demonstrates that Cry1 subclass efficiently kills lepidopterans due to complementarity of domain II loops to cadherin repeats conserved in caterpillar midguts. Cry1Aa, Cry1Ab, Cry1Ac share receptor binding epitopes recognizing glycosylated residues of cadherin CR12 and interaction with ABCC2 transporter facilitating membrane insertion. Larvae of Helicoverpa, Heliothis, Ostrinia, Pectinophora, and Plutella possess this receptor, making them highly susceptible even at low Cry concentrations expressed in transgenic leaf tissue. Activity against Coleoptera or Diptera is minimal because orthologous receptors differ in sequence. Laboratory bioassays measuring LC50 confirm Cry1 potency below 1 microgram per gram diet for many lepidopterans. This specificity guided deployment of Cry1Ac in cotton Bollgard protecting against bollworm complex and underscores order-specific nature of CryI toxins in integrated pest management programs reducing insecticide sprays. Field efficacy trials with Cry1Ac cotton show control of Helicoverpa armigera reducing insecticide sprays from six to one per season, preserving beneficial arthropods. Resistance monitoring uses diagnostic dose bioassays detecting shifts in LC50. Molecular characterization of receptor mutations in resistant strains shows cadherin truncation prevents binding. Hence CryI specificity to Lepidoptera underpins successful commercial deployment but requires resistance management via refuge planting and pyramiding strategies.
Ref: Bravo Ann Rev Entomol 2007 Cry1 lepidopteran; Tabashnik 1994 field; NCBI NBK24601; Crickmore 1998 specificity; PubMed 15012339.