By E. VinjeTweet
Bacillus thuringiensis Products
Bacillus thuringiensis (Bt) is a natural occurring, soil-borne bacteria that has been used since the 1950s for natural insect control. It consists of a spore, which gives it persistence, and a protein crystal within the spore, which is toxic. That toxic protein differs, depending on the subspecies of Bt producing it, yielding a variance of Bt toxic to different insect species (or none at all). When the bacteria is consumed by certain insects, the toxic crystal is released in the insects highly alkaline gut, blocking the system which protects the pest’s stomach from its own digestive juices. The stomach is penetrated, and the insect dies by poisoning from the stomach contents and the spores themselves. This same mechanism is what makes Bt harmless to birds, fish and mammals whose acidic gut conditions negate the bacteria’s affect.
Recently, Bt has been questioned because of its inclusion in Monsanto’s genetically modified corn and cotton. The difference between the Bt used by organic farmers around the world and that genetically inserted into Monsanto’s corn is dramatic. Naturally occurring Bt is contained within the bacterium. The Bt gene inserted into genetically-modified corn contains only the final toxin without its containment. Bt has a short half life when exposed to sunlight and the elements. By the time the insects that have consumed it are gone, so is the Bt. Its genetic counterpoint persists within the corn. Insects have developed immunity to the genetically-modified Bt–containing corn when the GMO corn has, against best agricultural practice, been planted in the same plot year after year. Targeted use of Bt insect control products used on appropriately managed plots have not resulted in insect resistance. Depending on which strain is used, Bt continues to be effective on cabbage worms, tent caterpillars, potato beetles, mosquitoes, black fly, and a variety of other insect pests.
Bt kurstaki (Bt-k) - Bacillus thuringiensis var kurstaki
Bt-k is a naturally occurring soil bacteria ideal for controlling tent caterpillars, gypsy moth, cabbage looper, tomato hornworm and other leaf eating caterpillars on trees, shrubs, tomatoes and other vegetables. Bt-k is most effective when applied to caterpillars during their 1st and 2nd instars, when they are still small. It must be ingested by the insect, as it is a stomach toxin. Harmless to humans, animals and beneficial insects. Bt-k biodegrades quickly in sunlight and may require reapplication under heavy insect pressure. To maximize effectiveness apply in the late afternoon. Several vendors offer Bacillus thuringiensis kurstaki that is approved or use in organic production.
Bt israelensis (Bt-i) - Bacillus thuringiensis var israelensis
Bt-i is a highly specific biological pesticide for use against mosquito, black fly and fungus gnat larvae. It may be applied safely to irrigation and roadside ditches, pastures, marshes and ponds, water gardens, flower pots, bird baths, rain gutters…any place there is standing water! Once ingested, Bt-i kills 95-100% of mosquito larvae within 24 hours. Highly effective because it kills these pests before they become biting adults. Will not harm people, pets, wildlife or fish. Mosquito Dunks are a commercial form of Bt-i.
Bt san diego (Bt-sd) - Bacillus thuringiensis var san diego and Bt tenebrionis (Bt-t) - Bacillus thuringiensis var tenebrionis
The Colorado potato beetle has developed unprecedented resistance to multiple applications of chemical insecticides. Bt-sd and Bt-t are toxic to a limited range of leaf-eating beetle species and are now considered to be the most effective control for this destructive insect pest. Can also be used to control the elm leaf beetle and may be used on potatoes, egg plant, tomatoes and elms. These biological pesticides should be applied to the young larval stages, as they have no effect on adult beetles. Safe for people, pets, wildlife or fish.
The milky spore disease of the Japanese beetle was the first microbial control to be developed commercially. Milky spore is the name of the disease to which Japanese beetle larvae succumb when attacked by Bacillus popilliae. The bacteria spreads naturally as each infected beetle larvae dies, decomposes and releases billions of new spores into the soil. Time must be allowed for this process to completely saturate a treated area, but only one application is required and the spores continue to multiply on their own, as long as larvae are present. When there is no longer a grub infestation, the spore remains dormant, waiting for subsequent populations.