Conservation ofBacillus thuringiensisefficacy in New Zealand through the planned deployment ofBtgenes in transgenic crops

Abstract

Although the use of Bacillus thuringiensis (Bt) as a foliar spray is minimal within New Zealand at present, a considerable effort is being made genetically to incorporate Bt δ-endotoxin genes into a wide range of important crops, including pasture species, perennial horticultural crops and annual field crops. For several years it has been clear that the major threat to the sustained efficacy of Bt in New Zealand is the evolution of insect resistance. Recognition of this threat has prompted consideration of a range of strategies for preventing and/or managing its possible evolution in pests of specific crops. However, such strategies do not address the critical issue of how we might limit the consequences of Bt resistance if it did evolve, particularly the evolution of resistance in polyphagous pests. Highly mobile polyphagous pests, such as leafroller species, might develop resistance to Bt on one transgenic crop and then disperse, nullifying the effectiveness of a wide range of Bt transgenic crops expressing the same or similar Cry proteins. Pests with resistance to CryIA proteins in transgenic plants might also display significant resistance to Bt biopesticides. To prevent such an eventuality in New Zealand we propose a plan for deploying Bt genes among crops according to an assessment of the risk and consequences of Bt resistance evolving in the insect complexes on these crops. The major elements of this plan are: (i) assess the risk of Bt resistant insects evolving and dispersing out of the crop to infest others; (ii) characterize the diversity of Bt protein binding sites in the guts of key polyphagous pests; (iii) use the above information to deploy Bt genes among different transgenic crops in a pattern that minimizes the chance that any future Bt resistant cosmopolitan pests will be broadly cross-resistant to other Bt crops and/or Bt biopesticides.

Resistance to the potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), in potato (Solanum tuberosum ssp. tuberosum L.) tubers

“…However, the advent of genetically engineered cultivars should not preclude research on other technologies as transgenic crops may not be readily accepted by the public (Australian Food Council 1996). Development of insect resistance to the Bt toxins may also prove to be a problem (Wigley et al 1996). Resistance to this pest has been reported within unmanipulated potato cultivars tested in New Zealand (Fenemore 1980), Kenya (Ojero & Mueke 1985), Nepal (Gyawali 1989), Egypt (Doss 1984), and among primitive and wild accessions in Peru (Raman & Palacios 1982) and Israel (Juvik et al 1982).…”

Behavioral responses of lightbrown apple moth neonate larvae on diets containing Bacillus thuringiensis formulations or endotoxins

“…At present, commercial formulations of Bt are not used extensively in New Zealand apple production against tortricid pests like the lightbrown apple moth because Bt does not provide the level of pest control required for an export-oriented fruit market (Wearing & Hokkanen, 1994). Transgenic apples which express Bt genes are currently being developed with the aim of managing these tortricid pests in the context of an integrated pest management system (Wearing & Hokkanen, 1994;Wigley et al, 1994).…”

Response to purified Cry IB protein in lab-wild type crosses of lightbrown apple moth

“…The risk of resistance would therefore be most significant in areas with large areas of habitat with genetically modified plants. This point was elucidated by Wigley et al (1994), who recognised the risk of expressing the same toxin gene in several hosts of leafrollers, such as white clover, apples, kiwifruit and Pinus radiata.…”

“…Transgenic pest resistant plants therefore may be important components of future integrated pest management systems for many crops, including apples. Deployment of transgenic crops containing Bacillus thuringiensis (Bt) genes or other environmentally benign insecticidal proteins will undoubtedly have ecological consequences, including selection pressure for pest adaptation (Wearing and Hokannen 1994;Wigley et al 1994). Several major pest species have already developed resistance to Bt-endotoxins in the laboratory, and some have evolved widespread resistance to Bt biopesticides in the field, making studies of Bt-susceptibility essential to assessing the risk of resistance (Tabashnik 1994).…”

“…Resistance to organophosphates is also known in one native leafroller, Planotortrix octo (Wearing 1995). These pests have the potential to become resistant to Bt toxins, if inappropriate management of the Bt resource is used (Wigley et al 1994).…”