Modeling for Prediction and Management

Onstad, David W.

doi:10.1016/b978-0-12-396955-2.00014-x

Cited by 11 publications

(19 citation statements)

References 58 publications

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“…However, despite the success of Bt crops, sustainable control of pest populations is threatened by the evolution of resistance [13]. The challenge of deploying efficient management strategies to reduce the risk of rapid evolution of resistance to toxins arises as a major component of the worldwide use of Bt crops.…”

Section: Introductionmentioning

confidence: 99%

Dominant Inheritance of Field-Evolved Resistance to Bt Corn in Busseola fusca

et al. 2013

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Transgenic crops expressing Bacillus thuringiensis (Bt) toxins have been adopted worldwide, notably in developing countries. In spite of their success in controlling target pests while allowing a substantial reduction of insecticide use, the sustainable control of these pest populations is threatened by the evolution of resistance. The implementation of the “high dose/refuge” strategy for managing insect resistance in transgenic crops aims at delaying the evolution of resistance to Bt crops in pest populations by promoting survival of susceptible insects. However, a crucial condition for the “high dose/refuge” strategy to be efficient is that the inheritance of resistance should be functionally recessive. Busseola fusca developed high levels of resistance to the Bt toxin Cry 1Ab expressed in Bt corn in South Africa. To test whether the inheritance of B . fusca resistance to the Bt toxin could be considered recessive we performed controlled crosses with this pest and evaluated its survival on Bt and non-Bt corn. Results show that resistance of B . fusca to Bt corn is dominant, which refutes the hypothesis of recessive inheritance. Survival on Bt corn was not lower than on non-Bt corn for both resistant larvae and the F1 progeny from resistant × susceptible parents. Hence, resistance management strategies of B . fusca to Bt corn must address non-recessive resistance.

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Section: Introductionmentioning

confidence: 99%

Dominant Inheritance of Field-Evolved Resistance to Bt Corn in Busseola fusca

et al. 2013

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“…These fixed values of Bt reflected the trade‐off between long‐ and short‐term killing required for sustainable resistance management and were sensitive to the fecundity of the susceptible homozygote, the principal driver of population growth when the resistance allele is rare. In effect, the model behaves as if susceptibility is a renewable resource (Mitchell & Onstad 2014) and allocates space between the refuge and Bt crop in a manner that regulates the number of susceptible insects while maintaining the resistance allele beneath the critical threshold. The more rapidly susceptible insects are replaced, the more that can be exposed to Bt in a given generation without prompting rapid selection for resistance.…”

Section: Discussionmentioning

confidence: 99%

“…This continuous selection pressure favours the survival of individuals expressing some level of tolerance to control, eroding our future capacity to manage the pest. As most recently commercialized insecticides are variants of previously isolated or synthesized compounds and developing and launching a new pesticide is estimated to take over a decade (REX Consortium 2013), it is unreasonably optimistic to assume that there will always be an alternative product available when control fails (Mitchell & Onstad 2014). Therefore, the sustained control of insect populations over prolonged periods requires that the strength of selection for resistance be constrained and/or reduced (REX Consortium 2013).…”

Section: Introductionmentioning

confidence: 99%

“…In spite of the strengths of the high‐dose/refuge strategy, less understood threats to the efficacy of this approach are ecological effects such as intraspecific (within species) competition between insects within the refuge (Onstad, Shelton & Flexner 2014). Competition is predicted to accelerate the evolution of resistance when carrying capacities are low or density dependence is overcompensating.…”

Section: Introductionmentioning

confidence: 99%

“…Competition is predicted to accelerate the evolution of resistance when carrying capacities are low or density dependence is overcompensating. These conditions may be facilitated by the spatial subdivision imposed upon the landscape by the high‐dose/refuge strategy (Onstad, Shelton & Flexner 2014). Superficially, we would not anticipate insects in a managed field to be able to attain numbers such that their density became self‐limiting without also losing the majority of the available yield.…”

Section: Introductionmentioning

confidence: 99%

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Type of fitness cost influences the rate of evolution of resistance to transgenic Bt crops

Hackett

Bonsall

2016

Journal of Applied Ecology

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Summary The evolution of resistance to pesticides by insect pests is a significant challenge for sustainable agriculture. For transgenic crops expressing Bacillus thuringiensis (Bt), crystalline (Cry) toxins resistance evolution may be delayed by the high‐dose/refuge strategy in which a non‐toxic refuge is planted to promote the survival of susceptible insects. The high‐dose/refuge strategy may interact with fitness costs associated with resistance alleles to further delay resistance. However, while a diverse range of fitness costs are reported in the field, they are typically represented as a fixed reduction in survival or viability which is insensitive to ecological conditions such as competition. Furthermore, the potential dynamic consequences of restricting susceptible insects to a refuge which represents only a fraction of the available space have rarely been considered.We present a generalized discrete time model which utilizes dynamic programming methods to derive the optimal management decisions for the control of a theoretical insect pest population exposed to Bt crops. We consider three genotypes (susceptible homozygotes, resistant homozygotes and heterozygotes) and implement fitness costs of resistance to Bt toxins as either a decrease in the relative competitive ability of resistant insects or as a penalty on fecundity. Model analysis is repeated and contrasted for two types of density dependence: uniform density dependence which operates equally across the landscape and heterogeneous density dependence where the intensity of competition scales inversely with patch size and is determined separately for the refuge and Bt crop.When the planting of Bt is decided optimally, fitness costs to fecundity allow for the planting of larger areas of Bt crops than equivalent fitness costs that reduce the competitive ability of resistant insects.Heterogeneous competition only influenced model predictions when the proportional area of Bt planted in each season was decided optimally and resistance was not recessive. Synthesis and applications. The high‐dose/refuge strategy alone is insufficient to preserve susceptibility to transgenic Bacillus thuringiensis (Bt) crops in the long term when constraints upon the evolution of resistance are not insurmountable. Fitness costs may enhance the delaying effect of the refuge, but the extent to which they do so depends upon how the cost is realized biologically. Fitness costs which apply independently of other variables may be more beneficial to resistance management than costs which are only visible to selection under a limited range of ecological conditions.

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Development of a rapid assessment method for detecting insecticide resistance in spotted wing Drosophila (Drosophila suzukii Matsumura)

Timmeren

Sial

Lanka

et al. 2019

Pest Management Science

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BACKGROUND: Spotted wing Drosophila is an invasive pest of fruit crops in most production regions globally, and insecticides are commonly used for its control. The biology of this pest combined with repeated pesticide exposure increases the risk of resistance to insecticides. We tested malathion, methomyl, spinetoram, spinosad, and zeta-cypermethrin against multiple colonies from each state using a contact bioassay method to determine diagnostic doses for assessment of insecticide susceptibility in this species. These were used to test populations collected in Michigan and Georgia, USA. RESULTS: Concentrations required to reach 50% (LC 50 ) and 90% mortality (LC 90 ) were calculated for the tested populations, and male mortality consistently occurred at lower concentrations than female mortality. Fly mortality did not vary significantly among populations collected from unmanaged, organic, and conventional fields. Similar results were found using the diagnostic concentrations applied to glass jars. CONCLUSIONS: Using this method, samples of D. suzukii that are freshly caught or reared from fruit can be tested within 1 day for their mortality in response to discriminating doses of five key insecticides. This method can be used to inform proactive resistance management strategies within integrated pest management programs.

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Modeling for Prediction and Management

Cited by 11 publications

References 58 publications

Dominant Inheritance of Field-Evolved Resistance to Bt Corn in Busseola fusca

Dominant Inheritance of Field-Evolved Resistance to Bt Corn in Busseola fusca

Type of fitness cost influences the rate of evolution of resistance to transgenic Bt crops

Development of a rapid assessment method for detecting insecticide resistance in spotted wing Drosophila (Drosophila suzukii Matsumura)

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