Paper of the Month August 2018

Multidecadal, county-level analysis of the effects of land use, Bt cotton, and weather on cotton pests in China


Long-term changes in land use, climate, and agricultural technologies
may affect pest severity and management. The influences of
these major drivers can only be identified by analyzing long-term
data. This study examines panel data on land use, adoption of
genetically modified Bacillus thuringiensis (Bt) insect-resistant cotton,
weather, pest severity, and insecticide use on three major
cotton pests for 51 counties in China during 1991–2015. Bt cotton
had pervasive effects on the whole pest complex in cotton and its
management. Adoption resulted in major reductions in insecticide
use for bollworm control. The resulting restoration of aphid biological
control decreased aphid severity. However, mirid bugs,
which have few effective natural enemies in cotton, increased in
severity with warming May and reduced insecticide spraying
against bollworm. The effects of landscape on pest severity were
pest specific. The severity of cotton aphid and mirid bugs decreased
with higher land use diversity, but the severity of highly
polyphagous cotton bollworm was unrelated to land use diversity.
Shares of forest, water body, and unused land area were negatively
associated with the severity of mirid bugs, whereas cotton
bollworm responded positively to the shares of water body and
unused land area. Farmers sprayed insecticides at mild infestation
levels and responded aggressively to severe bollworm outbreaks.
Findings support the usefulness of Bt-based plant resistance as a
component of integrated pest management (IPM) but highlight
the potential for unexpected outcomes resulting from agroecosystem
feedback loops as well as the importance of climate.

Wei Zhang, Yanhui Lu, Wopke van der Werf, Jikun Huang, Feng Wu, Ke Zhou, Xiangzheng Deng, Yuying Jiang, Kongming Wu and Mark W. Rosegrant (2018) PNAS (online first)

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