Diversity in land use can support ecosystem services such as biological pest control and reduce the need for insecticides. How can such a system be applied in China where land is precious and the predominate focus has been on increasing productivity through use of insecticides and other chemicals.
As the world’s largest pesticide producer and consumer, China uses 1.3 million tons of pesticides annually – 2.5 times the global average usage per unit area. Chinese farmers have relied on chemical insecticides as their primary pest control method, with insecticides often applied in an indiscriminant fashion.
China is also the world’s largest cotton producer, a crop that accounts for a large share of insecticides used, both in aggregate and per hectare use, even after the extensive adoption of insect-resistant Bt cotton. Agriculture in China is characterized by highly disturbed agro-ecosystems, but diverse land use at the plot level is still common. Globalization and rural-to-urban migration however, is shifting land use towards monoculture systems, where the same crop is grown year after year. The concern is that such landscape simplification may result in even greater insect pest pressure, and thus even more insecticide use.
A natural pest control
The Center for Chinese Agricultural Policy (CCAP) of the Chinese Academy of Sciences and the International Food Policy Research Institute (IFPRI) conducted a study in China’s Hebei province on the effects of land use on the abundance of natural pest enemies at the landscape scale. Natural enemies are insects that feed on crop pests, protecting crops from pest damage and reducing the need for chemical insecticide use. The empirical research used a number of methods including, household survey, insect sampling, remote sensing and ground-truthing.
The results of the study indicated that in the Hebei province, high land use diversity itself is not associated with high density of ladybeetles in cotton, which are natural enemies of a pest called cotton aphid. Instead, areas growing large amounts of maize were associated with greater densities of ladybeetles. This may be because of the maize-wheat crop rotation in the studied areas. Maize and wheat both require fewer pesticides and may provide habitat support for natural enemies that can spill over to other crops, such as the cotton crop.
Working as a natural pest control agent, ladybeetles provide economic value to farmers. Initial results show that the estimated economic value of conserving one additional ladybeetle per 100 plants (above current level) is $4.96, much higher than the “total” cost of one additional kilogram of insecticides ($8.57/ha).
However, there is a clear lack of understanding and knowledge among farmers on the value of natural enemies for crop health, resulting in a number of missed opportunities.
Most farmers are not aware of the service provided by ladybeetles. The excessive use of insecticides by farmers in China has had detrimental consequences for natural enemies in cotton. For example, each additional kilogram of insecticide used per hectare of land (above the current level), results in a decrease in ladybeetle densities by 29.7 heads/ha. Furthermore, the majority of farmers surveyed did not account for the populations of natural enemies when making pesticide use decisions. Many farmers even mistakenly treated natural enemies, such as ladybeetles, as pests that require spray.
Better transfer of information to farmers is needed and can support the health of crops, the environment, and farmers themselves. Such information transfer, supplemented with technical support, calls for better targeted integrated pest management (IPM) effort, where priority should be given to areas where there is potential for using landscape diversity to enhance pest control services. A reduction in pesticide use can help reduce public health and environmental risks associated with chemical pollution. Farmers can also benefit from less exposure to toxic chemicals as well as increased profits by harnessing natural enemies and reducing the amount of money spent on pesticides. To achieve these goals, we need to think outside of the box to go beyond the traditional government-driven IPM support approach to consider options such as crop insurance and private-public partnership.
The study showed that certain crop land use has the potential to enhance the biological control of cotton pests in northern China, where non-crop areas such as forest, shrubs and bushes are scant. Coordinated habitat management at the landscape scale can potentially be economically viable, especially for organic producers who have to rely more on pest control services provided by natural enemies. But such coordinated action requires enabling institutional environment and science-based guidance, monitoring and evaluation. Policies and market-based approaches that encourage farmers to account for the human health and environmental costs of insecticides could help incentivize the adoption of habitat management. Central to this is economic studies that valuate the benefits of ecosystem services in relation to landscape diversity and the possible tradeoffs between the provisioning ecosystem services (e.g., lower crop yield) and the other ecosystem services that are also important to farmers and the society (e.g., higher populations of natural enemies and bees, lower chemical pollution).
This story is based on the blog Ladybeetles: Cotton’s secret ingredient written by Wei Zhang, Research Fellow at IFPRI.