title: Spatio-Temporal Variation in Landscape Composition May Speed Resistance Evolution of Pests to Bt Crops.
abstract: Transgenic crops that express insecticide genes from Bacillus thuringiensis (Bt) are used worldwide against moth and beetle pests. Because these engineered plants can kill over 95% of susceptible larvae, they can rapidly select for resistance. Here, we use a model for a pyramid two-toxin Bt crop to explore the consequences of spatio-temporal variation in the area of Bt crop and non-Bt refuge habitat. We show that variability over time in the proportion of suitable non-Bt breeding habitat, Q, or in the total area of Bt and suitable non-Bt habitat, K, can increase the overall rate of resistance evolution by causing short-term surges of intense selection. These surges can be exacerbated when temporal variation in Q and/or K cause high larval densities in refuges that increase density-dependent mortality; this will give resistant larvae in Bt fields a relative advantage over susceptible larvae that largely depend on refuges. We address the effects of spatio-temporal variation in a management setting for two bollworm pests of cotton, Helicoverpa armigera and H. punctigera, and field data on landscape crop distributions from Australia. Even a small proportion of Bt fields available to egg-laying females when refuges are sparse may result in high exposure to Bt for just a single generation per year and cause a surge in selection. Therefore, rapid resistance evolution can occur when Bt crops are rare rather than common in the landscape. These results highlight the need to understand spatio-temporal fluctuations in the landscape composition of Bt crops and non-Bt habitats in order to design effective resistance management strategies.
authors.affiliation: Department of Zoology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Ives
authors.affiliation: CSIRO, Brisbane, Queensland, Australia.
authors.forename: Cate
authors.initials: C
authors.lastname: Paull
authors.affiliation: CSIRO, Brisbane, Queensland, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Hulthen
authors.affiliation: CSIRO, Narrabri, New South Wales, Australia.
authors.forename: Sharon
authors.initials: S
authors.lastname: Downes
authors.affiliation: Department of Entomology, University of Minnesota, St. Paul, Minnesota, United States of America.
authors.forename: David A
authors.initials: DA
authors.lastname: Andow
authors.affiliation: Ronin Institute, Montclair, New Jersey, United States of America.
authors.forename: Ralph
authors.initials: R
authors.lastname: Haygood
authors.affiliation: School of Biological Sciences, The University of Queensland, St Lucia, Queensland, Australia.
authors.forename: Myron P
authors.initials: MP
authors.lastname: Zalucki
authors.affiliation: CSIRO, Brisbane, Queensland, Australia.
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Schellhorn
mesh_terms: D000383:Agriculture / Q000379:methods*; D000818:Animals; D001413:Bacillus thuringiensis; D001427:Bacterial Toxins / Q000235:genetics; D005075:Biological Evolution; D018556:Crops, Agricultural / Q000235:genetics; D017753:Ecosystem; D005260:Female; D003368:Gossypium / Q000235:genetics; D007305:Insecticide Resistance / Q000235:genetics*; D007814:Larva; D008297:Male; D009036:Moths / Q000235:genetics*; D030821:Plants, Genetically Modified; D011793:Queensland; D062211:Spatio-Temporal Analysis
chemical_list: D001427:Bacterial Toxins