In India first transgenic crop Bt cotton got approval for cultivation in 2002. But before that insect called bollworm was the most serious pest of cotton. There are mainly three types of bollworms that attack cotton, they are American bollworm, spotted bollworm, and pink bollworm. Due to the attack of this bollworm, farmers had to face huge losses and their expenses on pesticides also increased. Between that scientists develop Bt cotton by using genetic engineering by inserting Bt genes from bacteria, bacillus thuringienisis. As a result, if a bollworm feeds on bt-cotton, an endotoxin goes into the stomach of the insect & ultimately causes its death.

Resistance against Bt cotton:
But in nature, every organism has the freedom to defend itself. So, bollworms start developing resistance Showing changes among them & developing resistance against BT cotton generation after generation.

Refugia Strategy: -

To counter this resistance problem refugia strategy is developed. In 2017 especially in MH, it is observed that pink bollworm attacks on bt-cotton as well. So GEAC 9Generic Engineering Appraisal Committee) develop Refugia in a bag concept. In this technique, it is recommended that Instead of planting the whole field with Bt cotton, plant 5 lines at the boundary of the field with non-Bt/ Desi cotton or pigeon pea crop. The government made it compulsory to plant 20% of the area with non-Bt crops & along with a bag of 450 gm of Bt seeds, and 25 gm of non-Bt seeds are provided.

The main concept behind this is, that resistance develops by a recessive gene. Insect feeding. on the non-bt crop are susceptible & those feeding on bt show resistance. After mating between them In the next generation progeny is susceptible (does not show resistance against Bt) as recessive gene doesn’t express in F1 generations.

Advantages:

Using this refugia strategy, the loss that farmers face due to the bollworm outbreaks can be prevented. Also, their extra expenses on insecticides can be reduced up to zero. 

Conclusion:

Growing refugia and non-Bt cotton in about 20@ of Bt cotton cultivated area is necessary for avoiding the outbreaks of bollworms resistant to Bt cotton. Insecticidal spray should be avoided because the purpose of planting refugia crops is to maintain the susceptible bollworm population.