The most widely grown cotton species is Gossypium hirsutum (American upland cotton), a high-yielding variety with long fibres, which today constitutes 80% of all production worldwide.

The extra long-staple specie of Gossypium barbadense (Sea Island cotton) is very demanding in terms of irrigation and climatic conditions, and only grows in a few countries, e.g. in Egypt and the United States, accounting for 15% of world production. A lot of small farmers, however, prefer local varieties (most of them from G. herbaceum) which provide lower yields but are more robust and more tolerant to pests. There are lower economic risks for farmers involved when they grow these varieties.

Genetically modified organisms are not allowed in organic agriculture. Bt cotton, for example Bollgard II, contains genes of the bacteria Bacillus thuringensis, which makes the plant produce an insecticide that prevents bollworms from feeding on it. Pests frequently develop resistance however, making it necessary to use of pesticides again and rendering Bt sprays less effective.

Furthermore, Bt cotton seeds are considerably more expensive and usually require high inputs of fertilizer and pesticides against sucking pests, thus increasing the financial risk of farmers.

Further reading:

Wikipedia : Gossypium

Natually colored cotton

India : Bt cotton devastated by secondary pests

China: Bt cotton linked with surge in crop pest