The major agronomic attribute of Bt cotton over conventional cotton is its ability to produce significantly higher yields in the presence of infestations of the major lepidopteran pests. This reflects Bt cotton’s higher level of resistance conferred by Bt genes, particularly to the bollworm complex. Higher yields, plus decreased insect control costs are usually the principal contributors to the increased profitability of Bt cotton. Given that pest infestations vary significantly from country to country and year to year, yield advantage of Bt cotton would also be expected to be highly variable. The data in Table 53 list the average increases in yield (expressed as a percentage of the corresponding non-Bt yield) in eight countries that have approved and now grow Bt cotton commercially. It is evident that the yield increases are highly variable and there are several features that deserve comment.

Acknowledging that to-date results are based only on field experiments, it is notable that India, a country situated in the tropics, has reported some of the highest average increases in yield associated with Bt cotton. Naik (2001) has reported an average increase of 38%; similar high increases in yield have been consistently reported for extensive multi-year, multi-locational field trials in India. In 2001 when cotton insect pest infestation was severe in India, yield increases in experiments were exceptionally high, up to 90% (ICAR 2002). On the contrary, China, a temperate country which also suffers from heavy pest infestations that sometimes require up to 28 to 30 sprays per season, has consistently reported more modest yield increases of 5 to 10% (Pray et al 2002, 2001). Yield increases for China are slightly lower than the US where the average increase is estimated at about 10% or more (Benedict and Altman 2001). Finally, Australia which normally has to apply 10 or more sprays to control heavy infestations has reported no significant increases in yield over the four year period, 1996/1997 to 1999/2000 (Fitt 2002 In Press). More detailed information on yield increases for specific countries are found in the country case studies on pages 85 to 136 of this publication.

The literature is replete with confirmations that Bt cotton provides improved pest control of the major lepidopteran pests resulting in significant increases in yield (Carpenter et al 2002, Pray et al 2002, Ismael et al 2002a,b,c, Benedict and Altman 2001, Edge et al 2001, Traxler et al 2001). In the US alone, Bt cotton increased lint production by 80,704 MT in 1998, 117,935 MT in 1999 and 84,085 MT in 2001 for a total of 282,724 MT more lint for a three year period (Gianesi et al 2002, Carpenter and Gianessi 2001) Table 54. In the US in 2001 the increase in lint due to Bt cotton was valued at $115 million, equivalent to about 3% of the total annual production of lint in the US, valued at about $4 billion. In China, the increase in seed cotton (which is about three times the weight of lint) for 1999 was 80,000 MT on 0.4 million hectares and 514,00 MT on 1.5 million hectares in 2001.