How does Btk work?
The Btk bacterium produces a protein crystal during the spore-forming stage of its life cycle which is toxic only to the larvae (caterpillars) of specific insect species. These microscopic crystals are ingested by insects when they are feeding on foliage treated with Btk. In the alkaline environment of the susceptible insect’s digestive system, the crystals are converted into toxic protein molecules that destroy the walls of the insect’s stomach. The insect usually stops feeding within hours and dies within two to five days. Btk works only against a group of insects called lepidopterans, which includes such destructive tree pests such as gypsy moths, spruce budworms and forest tent caterpillars. These pests are responsible for defoliating many trees in both urban areas and in forests. Other subspecies of Btk are registered for commercial use in Canada and these too work only on specific species of insect. For example, Btk subspecies israelensis (Bti) is active solely on mosquito and bl
