So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism’s pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Bacillus thuringiensis and Its Pesticidal Crystal Proteins

Botanical insecticides have long been touted as attractive alternatives to synthetic chemical insecticides for pest management because botanicals reputedly pose little threat to the environment or to human health. The body of scientific literature documenting bioactivity of plant derivatives to arthropod pests continues to expand, yet only a handful of botanicals are currently used in agriculture in the industrialized world, and there are few prospects for commercial development of new botanical products. Pyrethrum and neem are well established commercially, pesticides based on plant essential oils have recently entered the marketplace, and the use of rotenone appears to be waning. A number of plant substances have been considered for use as insect antifeedants or repellents, but apart from some natural mosquito repellents, little commercial success has ensued for plant substances that modify arthropod behavior. Several factors appear to limit the success of botanicals, most notably regulatory barriers and the availability of competing products (newer synthetics, fermentation products, microbials) that are cost-effective and relatively safe compared with their predecessors. In the context of agricultural pest management, botanical insecticides are best suited for use in organic food production in industrialized countries but can play a much greater role in the production and postharvest protection of food in developing countries.

/pdf/botanical-insecticides-deterrents-and-repellents-in-modern-5flrsy0hec.pdf

Botanical insecticides, deterrents, and repellents in modern agriculture and an increasingly regulated world

Human-mediated species invasions are a significant component of current global environmental change. There is every indication that the rate at which locations are accumulating non-native species is accelerating as free trade and globalization advance. Thus, the need to incorporate predictive models in the assessment of invasion risk has become acute. However, finding elements of the invasion process that provide consistent explanatory power has proved elusive. Here, we propose propagule pressure as a key element to understanding why some introduced populations fail to establish whereas others succeed. In the process, we illustrate how the study of propagule pressure can provide an opportunity to tie together disparate research agendas within invasion ecology.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(05)00032-7.pdf

The role of propagule pressure in explaining species invasions.

Conservation biologists assign population distinctiveness by classifying populations as evolutionarily significant units (ESUs). Historically, this classification has included ecological and genetic data. However, recent ESU concepts, coupled with increasing availability of data on neutral genetic variation, have led to criteria based exclusively on molecular phylogenies. We argue that the earlier definitions of ESUs, which incorporated ecological data and genetic variation of adaptive significance, are more relevant for conservation. Furthermore, this dichotomous summary (ESU or not) of a continuum of population differentiation is not adequate for determining appropriate management actions. We argue for a broader categorization of population distinctiveness based on concepts of ecological and genetic exchangeability ( sensu Templeton).

Considering evolutionary processes in conservation biology.

Mode d'acquisition de la resistance, repartition des individus sensibles et des individus resistants

Ecological Genetics of Insecticide and Acaricide Resistance

▪ Abstract Transgenic plants expressing insecticidal proteins from the bacterium, Bacillus thuringiensis (Bt), are revolutionizing agriculture. Bt, which had limited use as a foliar insecticide, has become a major insecticide because genes that produce Bt toxins have been engineered into major crops grown on 11.4 million ha worldwide in 2000. Based on the data collected to date, generally these crops have shown positive economic benefits to growers and reduced the use of other insecticides. The potential ecological and human health consequences of Bt plants, including effects on nontarget organisms, food safety, and the development of resistant insect populations, are being compared for Bt plants and alternative insect management strategies. Scientists do not have full knowledge of the risks and benefits of any insect management strategies. Bt plants were deployed with the expectation that the risks would be lower than current or alternative technologies and that the benefits would be greater. Based on th...

/pdf/economic-ecological-food-safety-and-social-consequences-of-1amli4lwvq.pdf

Economic, ecological, food safety, and social consequences of the deployment of bt transgenic plants.

Transgenic plants expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) were first commercialized in 1996 amid concern from some scientists, regulators and environmentalists that the widespread use of Bt crops would inevitably lead to resistance and the loss of a 'public good,' specifically, the susceptibility of insect pests to Bt proteins. Eight years later, Bt corn and cotton have been grown on a cumulative area >80 million ha worldwide. Despite dire predictions to the contrary, resistance to a Bt crop has yet to be documented, suggesting that resistance management strategies have been effective thus far. However, current strategies to delay resistance remain far from ideal. Eight years without resistance provides a timely opportunity for researchers, regulators and industry to reassess the risk of resistance and the most effective strategies to preserve Bt and other novel insect-resistant crops in development.

/pdf/insect-resistance-management-in-gm-crops-past-present-and-1tt7v8db41.pdf

Insect resistance management in GM crops: past, present and future

Transgenic crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) grew on >62 million ha worldwide from 1996 to 2002. Despite expectations that pests would rapidly evolve resistance to such Bt crops, increases in the frequency of resistance caused by exposure to Bt crops in the field have not yet been documented. In laboratory and greenhouse tests, however, at least seven resistant laboratory strains of three pests (Plutella xylostella [L.], Pectinophora gossypiella [Saunders], and Helicoverpa armigera [Hubner]) have completed development on Bt crops. In contrast, several other laboratory strains with 70- to 10,100-fold resistance to Bt toxins in diet did not survive on Bt crops. Monitoring of field populations in regions with high adoption of Bt crops has not yet detected increases in resistance frequency. Resistance monitoring examples include Ostrinia nubilalis (Hubner) in the United States (6 yr), P. gossypiella in Arizona (5 yr), H. armigera in northern China (...

https://bioone.org/journals/journal-of-economic-entomology/volume-96/issue-4/0022-0493-96.4.1031/Insect-Resistance-to-Transgenic-Bt-Crops--Lessons-from-the/10.1603/0022-0493-96.4.1031.pdf

Insect Resistance to Transgenic Bt Crops: Lessons From the Laboratory and Field

Resistance detection and documentation: the relative role of pesticidal and biochemical assays - Richard H. French-Constant and Richard T. Roush Investigating mechanisms of insecticide resistance: methods, strategies and pitfalls - Jeffrey G. Scott Molecular mechanisms of resistance - David M. Soderlund and Jeffrey R. Bloomquist The role of population genetics in resistance research and management - Richard T. Roush and Joanne C. Daly Modelling and evaluation of resistance management tactics - Bruce E. Tabashnik The effect of agrochemicals on vector populations - George P. Georghiou Pesticide resistance in arthropod natural enemies: variability and selection responses - Marjorie A. Hoy Management of pyrethroid-resistant tobacco budworms on cotton in the United States - Frederick W. Plapp, Jr., Clayton Campanhola, Ralph D. Bagwell and William F. McCutcheon Resistance management in multiple-pest orchard ecosystems in Eastern North America - David J. Pree Developing a philosophy and program of pesticide resistance management - Brian A. Croft.

Richard T. Roush

Papers

Ecological Genetics of Insecticide and Acaricide Resistance

Economic, ecological, food safety, and social consequences of the deployment of bt transgenic plants.

Insect resistance management in GM crops: past, present and future

Insect Resistance to Transgenic Bt Crops: Lessons From the Laboratory and Field

Pesticide resistance in arthropods.