Uses of Bt insect resistance in agriculture
This remarkable finding which happened in 1911 was not the first time Bt went under close inspection; in the Far East, ten years before, a Japanese scientist who was investigating the almost instantaneous death of silkworms first discovered it.
More than a century has now passed since Bt's discovery, and for more than half of it, Bt has been used as a natural insecticide, being sprayed onto crops. (Shelton 2008) But just how does Bt work in the first place'
Unlike Dichlorodiphenyltricloroethane, which has been known to be a three-letter acronym for the words notorious killer because of its infamousness in inflicting damage to organisms it should not, Bt is not a contact poison. Bt has to be eaten first before it can poison any unsuspecting insect. B. thuringiensis has spores which contain crystal proteins or cry proteins. When ingested by an insect, the active insecticidal crystal protein or (ICP) breaks down in the insect's gut and releases a toxin called delta-endotoxin. This delta-endotoxin then reacts with certain receptors on the intestinal lining and makes pores causing the leakage of its contents and paralyzation of the insect's digestive system resulting to insect death. The killing is a slow process that may take hours or even days. (Shelton 2008) However, it must be noted that because of the paralysis of the insect’s digestive system, the insect soon stops eating. Immediately dead or not, the goal of saving the crops from mass mastication of unwanted living forms is definitely achieved. (Office of Biotechnology at Iowa State University 2008)
Bt may not be as fast a killer as the conventional insecticides are, but in this ever health conscious world, speed is not the only thing to consider. Synthetic insecticides such as those whose active ingredient is DDT have been banned in many countries and for a number of good reasons. And it is because of such reasons why many farmers choose Bt over it; human safety, of course, is the primary concern. (Bassein 2008)
As mentioned, Bt has been used for more than 50 years now as an effective insecticide. So far, there are no reports of it harming anyone. And the underlying reason according to experts is the fact that Bt toxins are toxic only to certain insects; truly, this is good news for bees and beekeepers alike. The rationale' The receptors which are present in the insects' guts are not found in most other organisms, in mammals, and most importantly, in humans. (Federal Ministry of Education and Research 2008)
The different strains of B. thuringiensis produce different delta-endotoxins, each "catering" to a specific order of insect. The most common of Bt's cry proteins are those that belong to the Cry1 class which are toxic to lepidopterous insects (e.g. moths such as the European corn borer, butterflies). It is also the most active ingredient in most Bt-based commercial insecticides today. Other proteins belong to the Cry2 class which unlike their Cry1 counterparts, produce a single, smaller crystal per cell. This class is toxic to insects belonging in both the Lepidoptera and Diptera (e.g. flies and mosquitoes) orders. There is also the Cry3 class which poisons the coleopterous (e.g. beetles like the