THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
Dear Friends and Colleagues
Climate Change Can Increase Spread and Hardiness of Bt-Resistant Crop Pests
Genetically engineered Bt crops are planted across 28 countries reaching about 178 million hectares in 2015. The development of resistance in the insect pests is the major threat to the sustainability of the Bt technology. Two studies have examined the impacts of climate change on the target pests of Bt crops.
The first study (Item 1) in the US analysed the relationship of temperature anomaly (climate change) and Bt adoption with field-evolved resistance to Cry1Ab Bt sweet corn in a major pest, Helicoverpa zea. Itfound that temperature anomaly and its interaction with increased Bt adoption accelerated field-evolved resistance in H. zea to Bt corn expressing the Cry1Ab toxin. At the local spatial scale, increased feeding at high temperatures resulted in high injury to Bt sweet corn. High temperatures can stress Bt crops and possibly degrade soluble proteins, resulting in a decline of Cry1A toxin expression by the plant, and thereby, reduced field efficacy. The risk of Bt-resistant H. zea spreading is high given extensive Bt adoption, and the expected increase in overwintering and migration.
The second study (Item 2) examined Spodoptera exigua, a secondary target pest of Bt cotton in China. With the continuous adoption of Bt cotton, populations of S. exigua have gradually increased. The study found that a Bt-resistant S. exigua strain could survive better at suboptimal low temperature. It further found that the supercooling and freezing points of Bt-resistant S. exigua pupae were both significantly lower than that of the Bt-susceptible strain. These results indicate that Bt-resistant S. exigua has better cold tolerance. This means that the Bt-resistant secondary target pests could more easily overcome the overwinter season and become a source of crop damage the following year.
Both these studies highlight the need to incorporate evolutionary processes affected by climate change into Bt-resistance management programmes.
With best wishes,
Third World Network
131 Jalan Macalister
10400 Penang
Malaysia
Email: twn@twnetwork.org
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Item 1
CLIMATE CHANGE, TRANSGENIC CORN ADOPTION AND FIELD-EVOLVED RESISTANCE IN CORN EARWORM
Venugopal, P. D., & Dively, G. P.
Royal Society Open Science, 4(6), 170210.
DOI: 10.1098/rsos.170210
http://rsos.royalsocietypublishing.org/content/4/6/170210
7 June 2017
Abstract
Increased temperature anomaly during the twenty-first century coincides with the proliferation of transgenic crops containing the bacterium Bacillus thuringiensis (Berliner) (Bt) to express insecticidal Cry proteins. Increasing temperatures profoundly affect insect life histories and agricultural pest management. However, the implications of climate change on Bt crop–pest interactions and insect resistance to Bt crops remains unexamined. We analysed the relationship of temperature anomaly and Bt adoption with field-evolved resistance to Cry1Ab Bt sweet corn in a major pest, Helicoverpa zea (Boddie). Increased Bt adoption during 1996–2016 suppressed H. zea populations, but increased temperature anomaly buffers population reduction. Temperature anomaly and its interaction with elevated selection pressure from high Bt acreage probably accelerated the Bt-resistance development. Helicoverpa zea damage to corn ears, kernel area consumed, mean instars and proportion of late instars in Bt varieties increased with Bt adoption and temperature anomaly, through additive or interactive effects. Risk of Bt-resistant H. zea spreading is high given extensive Bt adoption, and the expected increase in overwintering and migration. Our study highlights the challenges posed by climate change for Bt biotechnology-based agricultural pest management, and the need to incorporate evolutionary processes affected by climate change into Bt-resistance management programmes.
Item 2
BETTER COLD TOLERANCE OF BT-RESISTANT SPODOPTERA EXIGUA STRAIN AND THE CORRESPONDING COLD-TOLERANT MECHANISM.
Honghua, S., Jincheng, Z., Qiuxia, Z., Qi, Y., Yong, Y., & Yizhong, Y. (2017).
Elsevier. https://doi.org/10.1016/j.pestbp.2017.06.003
http://www.sciencedirect.com/science/article/pii/S0048357517300482
7 June 2017
Highlights
• Found that Bt resistant Spodoptera exigua strain could survive better at suboptimal low temperature.
• Studied the cold hardiness of Bt resistant S. exigua strain and the cold tolerance mechanism.
• Found that the supercooling point and the freezing point of the Bt-resistant S. exigua pupae were lower
• Indicates that Bt-resistant S. exigua has better cold tolerance.
• Speculated that more anti-freeze substances, especially glycerol, were accumulated after continuously fed on Bt protein.
Abstract
Spodoptera exiguais a secondary target pest of Bt cotton commercialized in China. With the continuous adoption of Bt cotton, populations of S. exigua have gradually increased. However, the cold tolerance ability of Bt-resistant S. exigua and the effect of continuous Bt diet on anti-cold materials are unknown. In our study, it was found that Bt-resistant S. exigua (Bt10) developed better with shorter larval and pupal duration and higher pupation rate compared to CK at the suboptimal low temperature. The supercooling points and freezing points of the Bt-resistant S. exigua strain were determined, and body water content and anti-cold materials such as total sugar, trehalose and glycogen, glycerol and fat were examined to explore the effect of Bt toxin on overwintering and on population increase. The results showed that the supercooling point and the freezing point of the Bt-resistant S. exigua pupae were both significantly lower than that of the Bt-susceptible strain. No difference was found in the body water content of pupae and adults between the two strains. Total sugar content of the Bt-resistant strain at both the pupal and adult stages was higher than that of the susceptible strain at the corresponding stages, and glycogen content of the Bt-resistant strain at the larval stage was higher than that of the susceptible larval S. exigua. Fat content of the Bt-resistant larvae, pupae and adults was for each higher than that of the susceptible strain, but the difference was not significant except for that of the 3rd instar larvae. Glycerol content of the Bt-resistant strain at larval, pupal and adult stages was for each higher than that of the corresponding life stages of the susceptible strain. It can be seen that more glycerol was accumulated in Bt-resistant S. exigua. The results indicate that Bt-resistant S. exigua has better cold tolerance. The contents of the anti-freeze substances of progeny, especially glycerol, were increased after previous generations were continuously fed on Bt protein, which means that the Bt-resistant secondary target pests could more easily overcome the overwinter season and become a source of crop damage the following year.