A poisonous past?

2 Jul 2013

Well, the UK Government has certainly thrown its weight behind GM. I cannot disagree with any of the arguments made but creating a clear picture of the advantages of the technology is not easy.

The reason I say this is because I learnt a lot about the boll weevil on my recent visit to a cotton plantation in Louisiana. This insect invaded the US cotton belt at the turn of the 20th century and all but ruined the industry.  It is estimated that during the 1920s and 1930s it reduced yields by around 50%.

Dusting Machinery for Cotton Boll Weevil ControlIt became nationally important and folk songs were written about it. Cotton farmers soon started to treat the crops with insecticides to try to control it. This was initially dusting the crop, by hand (see picture) or by horse driven machinery, with arsenic based salts that often included lead.

Then DDT was used and after that the organophosphates and then the pyrethroids were adopted. At one time, up to 15-20 insecticide applications a year were being made and weevil resistance to them was building up. It was in the late 1970s that experimental eradication zones were tested and this initiated the national eradication programme.

The eradication programme includes federal legislation stating that only registered growers who agree to take part in the scheme can grow cotton. Crops are monitored using pheromone traps and are only treated when necessary. This has resulted in the recovery in the number of natural predators. Farmers pay 70% of the cost of the programme and the federal government the remaining 30%.

The boll weevil originally came into Texas from Mexico in around 1892 and then spread across the cotton growing states. The eradication programme has successfully reversed this progress, starting at the extremities of its spread and gradually pushing back the pest to Texas. Now many states are free from the pest.  Texas and Northern Mexico have become the front line. The pest is more able to hang on in these areas because the very mild winters mean that volunteer cotton plants survive and host the pest during the summer. So, volunteers in other crops and also in roadsides and field edges are now destroyed.

There have been set-backs in these areas. Hurricane winds have blown the weevil into districts previously free of the pest. Hence, monitoring continues in the weevil-free states. Also the activities of drug trafficking gangs on the Mexican-Texas border have limited the ability of the field workers to monitor the pest!
A measure of the success of the eradication programme is that overall the average number of insecticide applications in the crop has been reduced from 15-20/annum to around 2.8.

GM Bt cotton to protect the crop from weevil was first introduced in 1996 and now has a market share of over 70% of the area sown. So can all the reduction in insecticide spraying be claimed as being the result of its introduction?

There are two ways of looking at this. The eradication programme was introduced and was making good progress before the introduction of Bt cotton. Hence, claiming that all the reduction in insecticide spraying is due to Bt cotton is open to dispute. On the other hand, resistance to the synthetic insecticides was increasing and without the additional intervention of Bt cotton this may eventually have led to a break down in the programme.

I suppose there is another alternative to Bt cotton in combating the increasing resistance to the synthetic insecticides. The industry could return to the ‘good ol’ days’ when the ‘natural’ insecticides based on arsenic and lead were used. Given the choice, I think I would not be alone in preferring the Bt option.