Pest resistance to Cry1Ab Bt maize: Field resistance, contributing factors and lessons from South Africa


Angelika Hilbeck og Thomas Bøhn har publisert en ny artikkel.

Artikkelen tar opp den historiske utviklingen av resistens i skadeinsektet Buseola fusca mot genmodifisert (GM) Cry1Ab mais i Sør-Afrika, samt diskuterer de faktorene som har bidratt til den lite heldige utviklingen at MON810 mais ikke lenger er brukbar. Sør-Afrika har hatt en læringsprosess der kraften av seleksjon og hurtig evolusjonær endring i et pest-insekt til GM mais er tydelig illustrert. Kunnskapen om denne prosessen kan være verdifull for det vitenskapelige samfunnet og for forvaltningsmyndigheter i forhold til bruk av GM planter med Bt-toksiner mot insektskader.


This paper documents the historical development of resistance of the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae) to Bt maize (Zea mays L.). This pest was one of the first to evolve resistance to Bt maize expressing Cry1Ab protein. A time-line of events and contributing factors are presented, from the commencement of efficacy testing through to the present situation, where the Cry1Ab toxin has lost its efficacy against B. fusca at many localities throughout the maize producing region, and single-gene Bt maize events often require insecticide treatments for which farmers are compensated. Significant levels of pest survival on Bt maize was observed in the first season after commercial release in 1998 and confirmed seven years later. Reduced selection pressure on the target pest is the objective of insect resistance management (IRM), and strategies to accomplish this should receive highest priority. Where resistance is prevalent, the only viable options to reduce selection pressure are withdrawal of the product and/or enforcement of high-dose/refuge requirements. The latter action may however be of no value under conditions where resistance is prevalent, since the value of refugia to an IRM strategy may be compromised. Remedial actions taken in South Africa included the propagation and enforcement of refuge compliance followed by the release of pyramided maize hybrids in 2011. These pyramids combine Cry1A.105 and Cry2Ab2 toxin-producing transgenes, replacing the ineffective single-transgene. However, it remains uncertain if cross-resistance occurs between

Cry1A.105/Cry2Ab2 and the closely related Cry1Ab toxin, and for how long this pyramided event will endure. Cultivation of Cry1Ab-expressing hybrids continues in areas where resistance levels have been confirmed to be high. In retrospect, this case provides lessons regarding IRM, not only in South Africa, but wherever Bt crops are being introduced.

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