Dispelling the fears over Bt cotton

TM Manjunath | Updated on January 07, 2021

It has caused no scientifically validated ill-effects on humans, animals, or the environment anywhere in the world

Bt cotton was developed specifically to control bollworms, the most destructive of cotton crop pests. It has been under commercial cultivation since 1996 in the US and several other countries, and in India since March 2002.

In every country, including India, Bt cotton was subjected to rigorous bio-safety tests for 7-10 years to prove its safety to non-target beneficial organisms (like animals including mammals, birds, fish, earthworms, honey bees, parasitoids, and predators) and the environment before it was approved for commercial cultivation.

In spite of it, the safety of Bt cotton has been questioned by certain NGOs and individuals right from the beginning and it is continuing even now.

One of the most widely publicised allegations has been that the Bt which is incorporated in Bt cotton produces a toxin that is poisonous to humans, animals, other organisms and the environment and that if cattle or goats graze on such cotton plants, their health would be affected or even die and that their milk is hazardous.

All this has created a scare among people. Those spreading these rumours were mostly non-scientists who were not aware of the scientific background of Bt or even if they knew, they continued to do so out of some vested interest.

Here is an attempt to explain what is Bt, why is it safe, and what is its track record so that those who are looking for clarification would be benefited.

What is Bt?

Bt is the popular abbreviation for Bacillus thuringiensis, a beneficial bacterium found in the soil throughout the world. Its insecticidal property was discovered in Japan way back in 1901. More than 80 sub-species of B. thuringiensis have been described.

A unique feature of Bt is that certain gene(s) present in each sub-species can produce a distinct insecticidal crystalline (Cry) protein that would affect only a narrow range of insects belonging to a particular group. Thus, there are Bt proteins harmful to certain larvae of only Lepidoptera (moths and butterflies), Coleoptera (beetles), Diptera (flies), and so on. A particular Bt protein active on one group of insects generally does not affect other insects or other organisms, thus showing its unique host-specificity.

Depending upon the type of pests to be controlled and making use of the advances made in molecular biology and related sciences, the relevant Bt gene(s) can be identified, isolated, studied, modified and introduced into a plant. This process of introducing a new gene(s) derived from an external source — Bt, in this case — into a plant, although the two are not taxonomically related, is called genetic engineering (GE).

Such plants with Bt gene(s) are called ‘Bt plants’ or ‘Bt crops.’ For example, Bt cotton is incorporated with the Lepidopteron specific ‘Cry gene(s)’ as it is designed to control bollworms, which belong to this group. Similarly, genes possessing other specific biotic or abiotic traits can also be introduced into desired plants.

Specific conditions required

Since Bacillus thuringiensis is commonly present in the soil, many organisms would routinely come in contact with it. However, such external contact has no effect. Bt needs certain specific conditions:

Bt can become active only if it gets inside the body of an organism. For example, in the case of Bt cotton, when bollworm larvae feed on plant tissues, they ingest Bt protein.

When Bt is ingested, it will be in an insoluble and a passive state. The host should have an alkaline gut with a high pH of at least 9.5 for solubilising and activating the protein.

Further, the host should possess specific receptors in the mid-gut epithelial cells for the activated protein to bind. This results in damaging the membrane by creating pores, causing leakage of intestinal fluids, cessation of feeding by the insect and, finally, death.

All these conditions are available only in the susceptible insects — bollworms, in this case — and therefore they succumb when they feed on Bt plants. Bt proteins cannot act on humans, animals or other non-target organisms as they lack such specific conditions.

For example, the human gut is acidic, very low on pH and does not possess the required receptors. Numerous studies carried out in many countries have established that Bt is safe to them.

Despite this, the ‘antis’ continue to project Bt as if it is a general poison that would kill almost all organisms, thereby creating a psychological fear. They fail to appreciate its host-specificity. It is somewhat like this: If a patient is suffering from worms, the doctor may prescribe a medicine for de-worming. It kills only the worms, not the patient. Otherwise, it makes no sense.

Similarly, Bt protein in a Bt cotton plant will affect only the bollworms, not any other organisms or the plant.

Since its introduction in 1996, the global area under Bt cotton has steadily increased and, as of 2018, reached 24.8 million hectares (including 11.6 m ha in India) in about 14 countries that include the US, Brazil, Argentina, China, Australia and India as the major growers.

The benefits from Bt cotton in India included an increase in yield from 31 per cent to 67 per cent owing to effective control of bollworms, decrease in chemical insecticide use from 25 per cent to 55 per cent, net profit to farmers from ₹7,800 to ₹30,000/ha and, moreover, India turned from an importer to an exporter of cotton.

In spite of such extensive cultivation, Bt cotton has not caused any scientifically validated ill-effects on humans, animals, other non-target organisms or the environment anywhere in the world. Yet, the opponents continue to make the same old allegations that Bt cotton is not safe, undaunted by its impeccable safety records. Their pre-decided agenda is to oppose the technology.

It is high time that the governments took cognisance of the realistic scientific facts and made modern technologies available for the progress of farming and farmers.

The writer is a consultant in agri-biotechnology and integrated pest management

Published on January 07, 2021

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