Insect resistance to Bt crops: evidence versus theory

Evolution of insect resistance threatens the continued success of transgenic crops producing Bacillus thuringiensis (Bt) toxins that kill pests. The approach used most widely to delay insect resistance to Bt crops is the refuge strategy, which requires refuges of host plants without Bt toxins near Bt crops to promote survival of susceptible pests. However, large-scale tests of the refuge strategy have been problematic. Analysis of more than a decade of global monitoring data reveals that the frequency of resistance alleles has increased substantially in some field populations of Helicoverpa zea, but not in five other major pests in Australia, China, Spain and the United States. The resistance of H. zea to Bt toxin Cry1Ac in transgenic cotton has not caused widespread crop failures, in part because other tactics augment control of this pest. The field outcomes documented with monitoring data are consistent with the theory underlying the refuge strategy, suggesting that refuges have helped to delay resistance.     

Analytical methods for detecting pesticide switches with evolution of pesticide resistance

After a pest develops resistance to a pesticide, switching between different unrelated pesticides is a common management option, but this raises the following questions: (1) What is the optimal frequency of pesticide use? (2) How do the frequencies of pesticide applications affect the evolution of pesticide resistance? (3) How can the time when the pest population reaches the economic injury level (EIL) be estimated and (4) how can the most efficient frequency of pesticide applications be determined? To address these questions, we have developed a novel pest population growth model incorporating the evolution of pesticide resistance and pulse spraying of pesticides. Moreover, three pesticide switching methods, threshold condition-guided, density-guided and EIL-guided, are modelled, to determine the best choice under different conditions with the overall aim of eradicating the pest or maintaining its population density below the EIL. Furthermore, the pest control outcomes based on those three pesticide switching methods are discussed. Our results suggest that either the density-guided or EIL-guided method is the optimal pesticide switching strategy, depending on the frequency (or period) of pesticide applications.     

Haplodiploidy, sex, and the evolution of pesticide resistance

The assumption that males and females are equally tolerant to pesticides in haplodiploid arthropods led to the prediction that the evolution of resistance is faster in haplodiploid than in diploid arthropods. However, in this review, it was found that the ratio of male to female tolerance is substantially smaller in haplodiploid than in diploid arthropods, indicating that resistance alleles are not strongly up-regulated in haploid males. In addition, males were generally less tolerant than females in both haplodiploid and diploid arthropods. Factors such as sexual size dimorphism and sex-dependent selection may account for the lower tolerance in males than in females. Little among-population variation in the ratio of male to female tolerance was found in three species. Moreover, the tolerance ratio generally remained unchanged by selection for resistance to pesticides, although significant among-species variation was present within arthropod orders. This indicates that sexual dimorphism in pesticide tolerance evolves at a slower rate than resistance to pesticides. Simulations considering between-sex differences in pesticide tolerance showed that resistance evolution can be slower in haplodiploids than in diploids. Recessive resistance, low male tolerance to pesticides, fitness costs expressed in males, and the use of refuges contributed in substantially delaying the evolution of resistance in haplodiploid arthropods. These findings cast a new perspective on the evolution of pesticide resistance in haplodiploid herbivores and natural enemies.     

The social determinants of mental health and disorder: evidence,prevention and recommendations

People exposed to more unfavourable social circumstances are more vulnerable to poor mental health over their life course, in ways that are often determined by structural factors which generate and perpetuate intergenerational cycles of disadvantage and poor health. Addressing these challenges is an imperative matter of social justice. In this paper we provide a roadmap to address the social determinants that cause mental ill health. Relying as far as possible on high-quality evidence, we first map out the literature that supports a causal link between social determinants and later mental health outcomes. Given the breadth of this topic, we focus on the most pervasive social determinants across the life course, and those that are common across major mental disorders. We draw primarily on the available evidence from the Global North, acknowledging that other global contexts will face both similar and unique sets of social determinants that will require equitable attention. Much of our evidence focuses on mental health in groups who are marginalized, and thus often exposed to a multitude of intersecting social risk factors. These groups include refugees, asylum seekers and displaced persons, as well as ethnoracial minoritized groups; lesbian, gay, bisexual, transgender and queer (LGBTQ+) groups; and those living in poverty. We then introduce a preventive framework for conceptualizing the link between social determinants and mental health and disorder, which can guide much needed primary prevention strategies capable of reducing inequalities and improving population mental health. Following this, we provide a review of the evidence concerning candidate preventive strategies to intervene on social determinants of mental health. These interventions fall broadly within the scope of universal, selected and indicated primary prevention strategies, but we also briefly review important secondary and tertiary strategies to promote recovery in those with existing mental disorders. Finally, we provide seven key recommendations, framed around social justice, which constitute a roadmap for action in research, policy and public health. Adoption of these recommendations would provide an opportunity to advance efforts to intervene on modifiable social determinants that affect population mental health.     

Essay: Letters,numbers, symbols and words: how to communicate grades of evidence and recommendations

THE GRADE WORKING GROUP IS DEVELOPING and evaluating a common, sensible approach to grading quality of evidence and strength of recommendations in health care. In this article, we discuss the advantages and disadvantages of using letters, numbers, symbols or words to represent grades of evidence and recommendations. Using multiple strategies, we searched for comparative studies of alternative ways of representing ordered categories in any context. In addition, we contacted experts and reviewed theoretical work and qualitative research on how best to communicate grades of any kind quickly and clearly. We were unable to identify health care research that addressed, either directly or indirectly, the best way to present grades of evidence and recommendations. We found examples of symbols used by government, commercial and consumer organizations to communicate quality of evidence or strength of recommendations, but no comparative studies. Although a number of grading systems are used in health care and other fields, there is little or no evidence of how well various presentations are understood. Before promoting the use of specific symbols, numbers, letters or words, the extent to which the intended message is comprehended should be evaluated. Organizations such as the Canadian Task Force on Preventive Health Care¹ and more than 100 other groups² use various systems of codes to communicate grades of evidence and recommendations. The codes fall primarily into 3 categories: letters (e.g., A, B, C, etc.), numbers (e.g., I, II, III, etc.) and mixed letters and numbers (e.g., Ia, Ib, IIa, etc.).Health care practitioners, especially students, are often puzzled by the message a grade conveys. For example, the administration of oral anticoagulation in patients with atrial fibrillation and rheumatic mitral valve disease receives various grades of recommendation from different organizations: Class I based on level B evidence by the American Heart Association,³ grade C recommendation based on level IV evidence by SIGN² and grade 1C+ (where the 1 indicates the balance between benefit and harm and C+ the methodological quality of the underlying evidence) by the American College of Chest Physicians.⁴ Thus, the various grading systems may not be fulfilling their intended function: to communicate a clear message, quickly and concisely. Indeed, if the same code, used by different systems, represents different meanings, bewilderment and incomprehension may result.We formed the GRADE Working Group with the hope of reaching agreement on a common, sensible approach to grading quality of evidence and strength of recommendations. We consider here the advantages and disadvantages of using letters, numbers, symbols or words to represent different grades.     

Phenotypic evidence for inducible multiple antimicrobial resistance in Salmonella choleraesuis

Multiple antimicrobial resistance (MAR) in Salmonella choleraesuis is becoming a major concern. It has been demonstrated that a MAR phenotype can be induced in Escherichia coli and other members of the Enterobacteriaceae by exposing the isolates to salicylates, various antimicrobials, or organic solvents used to combat and control bacterial infection. Therefore the purpose of the present study was to determine whether this marA-associated MAR-phenotype is inducible in S. choleraesuis. Isolates used in the present study were able to withstand toxic effects of the organic solvent cyclohexane naturally, or following exposure to the inducing compounds salicylate, tetracycline, or chloramphenicol. All isolates possessed fragments of marA with the predicted size of 408 bp when amplified using marA-specific primers by PCR. The resulting PCR products that were sequenced revealed that amplified S. choleraesuis marA was 99% and 85% homologous to the published Salmonella typhimurium and E. coli marA sequences respectively. Minimum inhibitory concentrations of tetracycline (P<0.08), chloramphenicol (P<0.001), rifampin (P<0.08), and nalidixic acid (P<0.001) against cyclohexane-tolerant mutants were significantly increased when compared with wild-type S. choleraesuis. Northern hybridization signals for both marA and acrB were increased in the induced isolates when compared to uninduced controls while soxS expression did not change between induced and uninduced cultures. The results suggest that marA is present in S. choleraesuis and a MAR-phenotype is inducible in S. choleraesuis presumably due to the overexpression of marA and acrB and not to the overexpression of soxS.     

Evolution of pesticide resistance: interactions between generation time and genetic, ecological, and operational factors

We used computer simulation modeling to clarify the relationship between generation time and the rate of evolution of pesticide resistance. We examined the influence of generation time under various assumptions about genetics, population dynamics and selection pressures. The simplest model demonstrated that the time required for resistance to evolve can be independent of generation time. However, interactions of generation time with genetic, biological and operational factors resulted in positive, negative, and U-shaped relationships between the number of generations per year and the time required for resistance to evolve. These results preclude any generalizations concerning the influence of generation time on resistance evolution. Some ability to predict the influence of generation time may still exist on a case-by-case basis if the context of the resistance episode can be specified.     

Ecology of a bolas spider,Mastophora hutchinsoni: phenology,hunting tactics,and evidence for aggressive chemical mimicry

Summary Bolas spiders are relatively rare members of the large family known as orb weavers. Instead of using a typical web to capture prey, late-stadia and adult female bolas spiders swing a droplet of adhesive on a thread at flying insects. Mastophora hutchinsoni (Araneae: Araneidae) is one of five Mastophora species known from the United States and occurs over much of eastern North America. It is univoltine in Kentucky and overwinters in the egg stage. Spiderling emerged in May, the diminutive males matured in late June and early July, and females matured in early September. Eggs were produced from late September to late October or early November. This report is the first complete documentation of the population phenology of any bolas spider. Newly-emerged M. hutchinsoni spiderlings did not use a bolas, but instead hunted by positioning themselves on the underside of leaf margins where they ambushed small arthropods that crawled along the leaf margins. Subadult and adult female M. hutchinsoni used a bolas to capture moths. Only male moths were captured, specifically three species of Noctuidae (bristly cutworm, bronzed cutworm, and smoky tetanolita) and one species of Pyralidae (bluegrass webworm). Among 492 prey captured by more than twenty spiders at two sites during 1985 and 1986, smoky tetanolita moths and bristly cutworm moths accounted for 93% of the total. The flight behavior of approaching moths, the limited taxa caught from a large available moth fauna, and the fact that only males were caught support the hypothesis that the spider attracts its prey by producing chemicals which mimic the sex pheromones of these moth species. Adult female M. hutchinsoni frequently captured more than one moth species on a given night. The two most common prey species were active at different times of night, the bristly cutworm soon after nightfall and the smoky tetanolita generally between 11:00 p.m. and dawn. This pattern suggests that mating activity of these moth species may be temporally isolated, a common phenomenon when sympatric species have similar pheromones. If so, the spider could capture both species without producing different pheromone-mimicking compounds, simply by hunting during the activity period of each species.The investigation reported in this paper (No. 87-7-76) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

Fecundity selection theory: concepts and evidence

Fitness results from an optimal balance between survival, mating success and fecundity. The interactions between these three components of fitness vary depending on the selective context, from positive covariation between them, to antagonistic pleiotropic relationships when fitness increases in one reduce the fitness of others. Therefore, elucidating the routes through which selection shapes life history and phenotypic adaptations via these fitness components is of primary significance to understanding ecological and evolutionary dynamics. However, while the fitness components mediated by natural (survival) and sexual (mating success) selection have been debated extensively from most possible perspectives, fecundity selection remains considerably less studied. Here, we review the theoretical basis, evidence and implications of fecundity selection as a driver of sex‐specific adaptive evolution. Based on accumulating literature on the life‐history, phenotypic and ecological aspects of fecundity, we (i) suggest a re‐arrangement of the concepts of fecundity, whereby we coin the term ‘transient fecundity’ to refer to brood size per reproductive episode, while ‘annual’ and ‘lifetime fecundity’ should not be used interchangeably with ‘transient fecundity’ as they represent different life‐history parameters; (ii) provide a generalized re‐definition of the concept of fecundity selection as a mechanism that encompasses any traits that influence fecundity in any direction (from high to low) and in either sex; (iii) review the (macro)ecological basis of fecundity selection (e.g. ecological pressures that influence predictable spatial variation in fecundity); (iv) suggest that most ecological theories of fecundity selection should be tested in organisms other than birds; (v) argue that the longstanding fecundity selection hypothesis of female‐biased sexual size dimorphism (SSD) has gained inconsistent support, that strong fecundity selection does not necessarily drive female‐biased SSD, and that this form of SSD can be driven by other selective pressures; and (vi) discuss cases in which fecundity selection operates on males. This conceptual analysis of the theory of fecundity selection promises to help illuminate one of the central components of fitness and its contribution to adaptive evolution.     

Managing for multiple species: greater sage-grouse and sagebrush songbirds

Human activity has altered 33–50% of Earth's surface, including temperate grasslands and sagebrush rangelands, resulting in a loss of biodiversity. By promoting habitat for sensitive or wide-ranging species, less exigent species may be protected in an umbrella effect. The greater sage-grouse (Centrocercus urophasianus; sage-grouse) has been proposed as an umbrella for other sagebrush-obligate species because it has an extensive range that overlaps with many other species, it is sensitive to anthropogenic activity, it requires resources over large landscapes, and its habitat needs are known. The efficacy of the umbrella concept, however, is often assumed and rarely tested. Therefore, we surveyed sage-grouse pellet occurrence and sagebrush-associated songbird abundance in northwest Colorado, USA, to determine the amount of habitat overlap between sage-grouse and 4 songbirds (Brewer's sparrow [Spizella breweri], sage thrasher [Oreoscoptes montanus], sagebrush sparrow [Artemisiospiza nevadensis]), and green-tailed towhee [Pipilo chlorurus]). During May and June 2013–2015, we conducted standard point count breeding surveys for songbirds and counted sage-grouse pellets within 300 10-m radius plots. We modeled songbird abundance and sage-grouse pellet occurrence with multi-scaled environmental features, such as sagebrush cover and bare ground. To evaluate sage-grouse as an umbrella for sagebrush-associated passerines, we determined the correlation between probability of sage-grouse pellet occurrence and model-predicted songbird densities per sampling plot. We then classified the sage-grouse probability of occurrence as high (probability >0.5) and low (probability ≤0.5) and mapped model-predicted surfaces for each species in our study area. We determined average songbird density in areas of high and low probability of sage-grouse occurrence. Sagebrush cover at intermediate scales was an important predictor for all species, and ground cover was important for all species except sage thrashers. Areas with a higher probability of sage-grouse occurrence also contained higher densities of Brewer's sparrows, green-tailed towhees, and sage thrashers, but predicted sagebrush sparrow densities were lower in these areas. In northwest Colorado, sage-grouse may be an effective umbrella for Brewer's sparrows, green-tailed towhees, and sage thrashers, but sage-grouse habitat does not appear to capture areas that support high sagebrush sparrow densities. A multi-species focus may be the best management and conservation strategy for several species of concern, especially those with conflicting habitat requirements. © The Wildlife Society, 2019     

Grading quality of evidence and strength of recommendations

Users of clinical practice guidelines and other recommendations need to know how much confidence they can place in the recommendations. Systematic and explicit methods of making judgments can reduce errors and improve communication. We have developed a system for grading the quality of evidence and the strength of recommendations that can be applied across a wide range of interventions and contexts. In this article we present a summary of our approach from the perspective of a guideline user. Judgments about the strength of a recommendation require consideration of the balance between benefits and harms, the quality of the evidence, translation of the evidence into specific circumstances, and the certainty of the baseline risk. It is also important to consider costs (resource utilisation) before making a recommendation. Inconsistencies among systems for grading the quality of evidence and the strength of recommendations reduce their potential to facilitate critical appraisal and improve communication of these judgments. Our system for guiding these complex judgments balances the need for simplicity with the need for full and transparent consideration of all important issues.     

Multilevel selection theory and evidence: a critique of Gardner, 2015

Gardner (2015) recently developed a model of a ‘Genetical Theory of Multilevel Selection, which is a thoughtfully developed, but flawed model. The model's flaws appear to be symptomatic of common misunderstandings of the multi level selection (MLS) literature and the recent quantitative genetic literature. I use Gardner's model as a guide for highlighting how the MLS literature can address the misconceptions found in his model, and the kin selection literature in general. I discuss research on the efficacy of group selection, the roll of indirect genetic effects in affecting the response to selection and the heritability of group‐level traits. I also discuss why the Price multilevel partition should not be used to partition MLS, and why contextual analysis and, by association, direct fitness are appropriate for partitioning MLS. Finally, I discuss conceptual issues around questions concerning the level at which fitness is measured, the units of selection, and I present a brief outline of a model of selection in class‐structured populations. I argue that the results derived from the MLS research tradition can inform kin selection research and models, and provide insights that will allow researchers to avoid conceptual flaws such as those seen in the Gardner model.