Insecticide and other artificial chemical use in the field of agriculture is a hotly debated subject and is generally regarded to entail, at a minimum, some negative effects. Certainly much research has focused on uncovering avenues to reduce the prolific use of such chemicals, including work with genetically modified organisms (GMOs). Bt cotton is one widely implemented and successful example of a GMO; with more than 66,000,000 hectares (ha) of Bt cotton cultivated worldwide in 2011, it has certainly proved popular with both farmers and governments (Lu et al. 2012). Essentially, Bt cotton allows farmers to apply less pesticide to a crop throughout a season. The research performed by Lu et al. in north China focused on two main questions: first, whether Bt cotton implementation on a large scale resulted in an increase of generalist arthropod predators in Bt cotton fields as well as other neighboring crops. Second, this research looked for increased biocontrol in China as a potential result of increased predator populations. Ultimately, the research concluded that Bt cotton implementation, and more importantly the reduced usage of insecticides, positively affected predator density, negatively affected pest density, and produced some evidence that these effects spill over to neighboring fields.—Chad Redman
Lu, Y., Wu, K., Jiang, Y., Guo, Y., Desneuz, N., 2012. Widespread Adoption of Bt Cotton and Insecticide Decrease Promotes Biocontrol Services. Nature 487, 362–367.
Lu et al investigated the effects of using Bt cotton in order to reduce the need for pesticides on biological control services. Modern farming techniques are continually moving farther and farther away from biological control services to manage increasingly valuable and productive crops. However, manufactured chemicals may not always be the answer. Lu et al. surveyed arthropod predators and cotton aphid populations in northern China from 1990 to 2010 and performed experiments at the Langfang experimental station of the Chinese Academy of Agricultural Science (CAAS) from 2001 to 2011. Their research was geared at monitoring predators and aphids in Bt and non-Bt cotton fields, treating some of each with pesticide and leaving some of each without pesticide. The researchers also kept track of the predator abundance and insecticide use in cotton in 36 locations throughout northern China from 1990 to 2010. Additionally, aphid density was recorded in 24 places over the same time period in order to measure the biocontrol services rendered by predators. Finally, Lu et al. performed exclusion cage trials in the years 2010 and 2011.
Regarding the experiment in which researchers compared Bt and non-Bt cotton both with and without pesticide control, there was no significant difference found between the two crops when similar management methods were used; that is, the genetically modified cotton was no different than the unmodified cotton in this particular experiment. However, there was a striking difference between the predator and aphid populations in the insecticide treated crops versus the non-treated crops; those crops that were not treated had much lower pest populations. This is an exciting result because it means that the biological services of predators out performed our chemical control methods.
From 1990 to 2010, the cotton industry underwent many changes. Due to governmental mandates, Bt cotton became common in 1997 and this resulted in a spike in the predator population throughout north China. This also coincided with a drastic fall in the use of pesticides as well as the population of pests; more strong evidence that biocontrol is very effective. Moreover, the exclusion cage experiments further confirmed the hypotheses of Lu et al..
This study came to several conclusive realizations. It is evident that overusing pesticides can actually result in higher relative populations of pests compared to allowing several predator species to thrive and produce a biocontrol service. Less convincing, yet still compelling, are the data showing trends for these arthropod predators to migrate into neighboring fields, regardless of the particular crop in that adjacent field.