Deltamethrin resistance in the codling moth (Lepidoptera: Tortricidae): inheritance and number of genes involved

The inheritance of deltamethrin resistance in Cydia pomonella (L.) has been investigated by crossing a resistant (Rv) and a susceptible (Sv) strain, derived from a population collected in south-eastern France in 1995. Deltamethrin resistance was suspected to be under the control of a kdr-type allele and an enhanced mixed-function oxidase (mfo). F(1) and F(2) progenies were therefore tested through dose-response and enzyme assays. Dose-response relationships indicated that resistance was inherited as an autosomal incompletely recessive (D=-0.199) character, involving at least two genes. Enzyme measures suggested the contribution of 1.2 genes to the expression of mfo, with incomplete dominance (D=0.460). Our results support the hypothesis of a polygenic response to deltamethrin selection in the Rv strain, including a major kdr-type allele with a minor effect of mfos. In the light of these findings, we consider the resistance in codling moth populations in south-eastern France as a product of an adaptive sequential selection process, occurring through the sequential addition of resistance genes.

Constraints on adaptive mutations in the codling moth Cydia pomonella (L.): measuring fitness trade-offs and natural selection

Adaptive changes in populations encountering a new environment are often constrained by deleterious pleiotropic interactions with ancestral physiological functions. Evolutionary responses of populations can thus be limited by natural selection under fluctuating environmental conditions, if the adaptive mutations are associated with pleiotropic fitness costs. In this context, we have followed the evolution of the frequencies of insecticide-resistant mutants of Cydia pomonella when reintroduced into an untreated environment. The novel set of selective forces after removal of insecticide pressure led to the decline of the frequencies of resistant phenotypes over time, suggesting that the insecticide-adapted genetic variants were selected against the absence of insecticide (with a selective coefficient estimated at 0.11). The selective coefficients were also estimated for both the major cytochrome P450-dependent monooxygenase (MFO) and the minor glutathione S-transferase (GST) systems (0.17 and negligible, respectively), which have been previously shown to be involved in resistance. The involvement of metabolic systems acting both through xenobiotic detoxification and biosynthetic pathways of endogenous compounds may be central to explaining the deleterious physiological consequences resulting from pleiotropy of adaptive changes. The estimation of the magnitude of the fitness cost associated with insecticide resistance in C. pomonella suggests that resistance management strategies exclusively based on insecticide alternations would be unlikely to delay such a selection process.

Winter condition and proximate composition of anadromous arctic charr (Salvelinus alpinus) in eastern Ungava Bay, Quebec

Arctic charr (Salvelinus alpinus) were sampled during the winter of 1985–1986 in the Kangiqsualujjuaq area of northern Quebec to examine feeding patterns and temporal variation in condition. No feeding was observed at any time during the winter, and examination of gallbladder coloration indicated that feeding had not occurred for a long period of time. Proximate composition analysis of nonreproductive charr from Koroc River indicated that liver and muscle lipid and liver protein reserves changed during the winter fast, and this was most pronounced in early winter. Spent charr sampled at Lake Tasikallak had lower liver lipid and condition factor values and were more depleted than nonreproductive charr. Despite a reduction in lipids and protein during winter, the general condition of nonreproductive charr renders them suitable for commercial sale at any time of the year.

Dioxin reservoirs in southern Viet Nam--a legacy of Agent Orange

In the isolated Aluoi Valley of central Viet Nam, very high levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were measured in soil, fish fat, duck fat, pooled human blood and breast milk samples collected from A So village between 1996 and 1999. The village was situated on a former military base occupied by US Special Forces between 1963 and 1966. TCDD was a contaminant of the herbicide "Agent Orange", aerially sprayed in the valley between 1965 and 1970, and stored at the A So base. Measured levels were lower near the sites of two other former US bases in the valley which had been occupied for shorter periods of time. In areas where Agent Orange had been applied by low-flying aircraft, levels of TCDD in soil, food and human samples were elevated, but lower than those near the three former US bases. We confirm the apparent food chain transfer of TCDD from contaminated soil to cultured fish pond sediments to fish and duck tissues, then to humans as measured in whole blood and breast milk. We theorize that the Aluoi Valley is a microcosm of southern Viet Nam, where numerous reservoirs of TCDD exist in the soil of former military installations south of the former demilitarized zone. Large quantities of Agent Orange were stored at many sites, used in ground and aerial applications, and spilled. TCDD, through various forms of soil disturbance, can be mobilized from these reservoirs after decades below the surface, and subsequently, introduced into the human food chain.

Age-dependent response to insecticides and enzymatic variation in susceptible and resistant codling moth larvae

Insecticide resistance in the codling moth, Cydia pomonella, partly results from increased metabolic detoxification. The aim of this study was to follow the age variations in larval susceptibility to deltamethrin and teflubenzuron in one susceptible (S) strain, and two resistant (Rv and Rt) ones selected for resistance to deltamethrin and diflubenzuron, respectively. The age variation of the activities of cytochrome P450-dependent monooxygenase (MFO), glutathione S-transferases (GST), and esterases in S and both resistant strains were simultaneously investigated. The highest levels of insecticide resistance were recorded in late instars in both resistant strains, although Rv neonates exhibited enhanced resistance to deltamethrin. The involvement of an additional deltamethrin-specific mechanism of resistance, which could be mainly expressed in early instars, was supported by previous demonstration of a kdr point mutation in the Rv strain. The cross-resistance between deltamethrin and teflubenzuron indicated the involvement of non-specific metabolic pathways in resistance to teflubenzuron, rather than target site modification. A positive correlation between enhanced GST activities and deltamethrin resistance suggested that this mechanism might take place into the adaptive response of C. pomonella to pyrethroids treatments. Enhanced MFO activity was recorded in each instar of the two resistant strains compared to the susceptible one. But these activities were not correlated to the responses to deltamethrin nor to teflubenzuron. In the light of these findings, studying age-dependence of responses to selection is central to the implementation of monitoring tests of resistances, especially if the target instars are difficult to collect in the field.

Epidemiology of asexuality induced by the endosymbiotic Wolbachia across phytophagous wasp species: host plant specialization matters

Among eukaryotes, sexual reproduction is by far the most predominant mode of reproduction. However, some systems maintaining sexuality appear particularly labile and raise intriguing questions on the evolutionary routes to asexuality. Thelytokous parthenogenesis is a form of spontaneous loss of sexuality leading to strong distortion of sex ratio towards females and resulting from mutation, hybridization or infection by bacterial endosymbionts. We investigated whether ecological specialization is a likely mechanism of spread of thelytoky within insect communities. Focusing on the highly specialized genus Megastigmus (Hymenoptera: Torymidae), we first performed a large literature survey to examine the distribution of thelytoky in these wasps across their respective obligate host plant families. Second, we tested for thelytoky caused by endosymbionts by screening in 15 arrhenotokous and 10 thelytokous species for Wolbachia, Cardinium, Arsenophonus and Rickettsia endosymbionts and by performing antibiotic treatments. Finally, we performed phylogenetic reconstructions using multilocus sequence typing (MLST) to examine the evolution of endosymbiont-mediated thelytoky in Megastigmus and its possible connections to host plant specialization. We demonstrate that thelytoky evolved from ancestral arrhenotoky through the horizontal transmission and the fixation of the parthenogenesis-inducing Wolbachia. We find that ecological specialization in Wolbachia's hosts was probably a critical driving force for Wolbachia infection and spread of thelytoky, but also a constraint. Our work further reinforces the hypothesis that community structure of insects is a major driver of the epidemiology of endosymbionts and that competitive interactions among closely related species may facilitate their horizontal transmission.

Phenological segregation of insecticide resistance alleles in the codling moth Cydia pomonella (Lepidoptera: Tortricidae): a case study of ecological divergences associated with adaptive changes in populations

Intrapopulation variability in the seasonal regulation of insect lifecycles has been shown to be due partly to genetic changes. Selection for insecticide resistance in the codling moth Cydia pomonella results from allelic substitution at two to three loci in south-eastern French populations of this species. However, such an adaptive process has been associated with an increased heterogeneity in the developmental responses to climatic factors such as temperature. In this paper, we investigate whether such pleiotropic effects of resistance on development induce a significant discrepancy in seasonal regulation in this species. The seasonal changes in a susceptible and two insecticide-resistant homozygous genotypes of C. pomonella, as well as their reciprocal F1 progeny, were followed under natural conditions during the reproductive season through the emergence events of adults, within-generation developmental rates and the number of generations. A significant delay in the occurrences of homozygous resistant genotypes resulted from significantly lower pre-imaginal developmental times relative to homozygous susceptible ones. Subsequent assessment of the number of generations indicated significantly higher diapause propensities in carriers of the resistance alleles (37.0-76.2%) than in susceptible homozygotes (6-7%), which mostly pupated towards a third generation of adults. In the light of these findings, pleiotropic effects of adaptive changes might be a crucial source of divergence in seasonal regulation at the population level, involving significant life-history trade-offs. In addition to man-made selective factors during the reproductive season, such an effect on the lifecycle could be a key component in the process of selection for resistance genes in south-eastern France C. pomonella populations.

Is there tree senescence? The fecundity evidence

Despite its importance for forest regeneration, food webs, and human economies, changes in tree fecundity with tree size and age remain largely unknown. The allometric increase with tree diameter assumed in ecological models would substantially overestimate seed contributions from large trees if fecundity eventually declines with size. Current estimates are dominated by overrepresentation of small trees in regression models. We combined global fecundity data, including a substantial representation of large trees. We compared size-fecundity relationships against traditional allometric scaling with diameter and two models based on crown architecture. All allometric models fail to describe the declining rate of increase in fecundity with diameter found for 80% of 597 species in our analysis. The strong evidence of declining fecundity, beyond what can be explained by crown architectural change, is consistent with physiological decline. A downward revision of projected fecundity of large trees can improve the next generation of forest dynamic models.

Contrasted invasion processes imprint the genetic structure of an invasive scale insect across southern Europe

Deciphering the colonization processes by which introduced pests invade new areas is essential to limit the risk of further expansion and/or multiple introductions. We here studied the invasion history of the maritime pine bast scale Matsucoccus feytaudi. This host-specific insect does not cause any damage in its native area, but it devastated maritime pine forests of South-Eastern France where it was detected in the 1960s, and since then reached Italy and Corsica. We used population genetic approaches to infer the populations' recent evolutionary history from microsatellite markers and Approximate Bayesian Computation. Consistent with previous mitochondrial data, we showed that the native range is geographically strongly structured, which is probably due to the patchy distribution of the obligate host and the limited dispersal capacity of the scale. Our results show that the invasion history can be described in three successive steps involving different colonization and dispersal processes. During the mid-XXth century, massive introductions occurred from the Landes planted forest to South-Eastern France, probably due to transportation of infested wood material after World War II. Stepping-stone expansion, consistent with natural dispersal, then allowed M. feytaudi to reach the maritime pine forests of Liguria and Tuscany in Italy. The island of Corsica was accidentally colonized in the 1990s, and the most plausible scenario involves the introduction of a limited number of migrants from the forests of South-Eastern France and Liguria, which is consistent with an aerial dispersal due to the dominant winds that blow in spring in this region.

Reconstruction of a windborne insect invasion using a particle dispersal model, historical wind data, and Bayesian analysis of genetic data

Understanding how invasive species establish and spread is vital for developing effective management strategies for invaded areas and identifying new areas where the risk of invasion is highest. We investigated the explanatory power of dispersal histories reconstructed based on local-scale wind data and a regional-scale wind-dispersed particle trajectory model for the invasive seed chalcid wasp Megastigmus schimitscheki (Hymenoptera: Torymidae) in France. The explanatory power was tested by: (1) survival analysis of empirical data on M. schimitscheki presence, absence and year of arrival at 52 stands of the wasp's obligate hosts, Cedrus (true cedar trees); and (2) Approximate Bayesian analysis of M. schimitscheki genetic data using a coalescence model. The Bayesian demographic modeling and traditional population genetic analysis suggested that initial invasion across the range was the result of long-distance dispersal from the longest established sites. The survival analyses of the windborne expansion patterns derived from a particle dispersal model indicated that there was an informative correlation between the M. schimitscheki presence/absence data from the annual surveys and the scenarios based on regional-scale wind data. These three very different analyses produced highly congruent results supporting our proposal that wind is the most probable vector for passive long-distance dispersal of this invasive seed wasp. This result confirms that long-distance dispersal from introduction areas is a likely driver of secondary expansion of alien invasive species. Based on our results, management programs for this and other windborne invasive species may consider (1) focusing effort at the longest established sites and (2) monitoring outlying populations remains critically important due to their influence on rates of spread. We also suggest that there is a distinct need for new analysis methods that have the capacity to combine empirical spatiotemporal field data, genetic data, and environmental data to investigate dispersal and invasion.

Temporal population genetics of time travelling insects: a long term study in a seed-specialized wasp

Many animal species experiencing spatial or interannual fluctuations of their environment are capable of prolonged diapause, a kind of dormancy that extends over more than one year. Such a prolonged diapause is commonly perceived as a temporal demographic refuge in stochastic environments, but empirical evidence is still lacking of its consequences on temporal population genetic structures. In this long-term study, we investigated how a particular pattern of prolonged diapause may influence the temporal population genetics of the invasive seed-specialized wasp Megastigmus schimitscheki (Hymenoptera: Torymidae) in southeastern France. We characterized the diapause strategy of M. schimitscheki using records of emergence from diapause in 97 larval cohorts, and we conducted a temporal population genetic study on a natural invasive wasp population sampled during ten consecutive years (1999-2008) using polymorphic microsatellite markers. We found that M. schimitscheki can undergo a prolonged diapause of up to five years and displays two main adult emergence peaks after two and four years of diapause. Such a bimodal and atypical pattern did not disrupt temporal gene flow between cohorts produced in even and in odd years during the period of the study. Unexpectedly, we found that this wasp population consisted of two distinct genetic sub-populations that strongly diverged in their diapause strategies, with very few admixed individuals. One of the sub-populations displayed both short and prolonged diapause (2 and 4 years respectively) in equal proportions, whereas the other sub-population displayed mainly short diapause. This study provided empirical evidence that prolonged diapause phenotypes can substantially contribute to reproduction and impact temporal genetic structures. Prolonged diapause is likely to act as both demographic and genetic refuges for insect populations living in fluctuating environments.

Insecticide resistance may enhance the response to a host-plant volatile kairomone for the codling moth, Cydia pomonella (L.)

The behavioral and electroantennographic responses of Cydia pomonella (L.) to the ripe pear volatile ethyl (2E,4Z)-2,4-decadienoate (Et-E,Z-DD), were compared in insecticide-susceptible and -resistant populations originating from southern France. A dose-response relationship to this kairomonal attractant was established for antennal activity and did not reveal differences between susceptible and resistant strains. Conversely, males of the laboratory strains expressing metabolic [cytochrome P450-dependent mixed-function oxidases (mfo)] or physiological (kdr-type mutation of the sodium-channel gene) resistance mechanisms exhibited a significantly higher response to Et-E,Z-DD than those of the susceptible strain in a wind tunnel experiment. No response of the females to this kairomone could be obtained in our wind-tunnel conditions. In apple orchards, mfo-resistant male moths were captured at significantly higher rates in kairomone-baited traps than in traps baited with the sex pheromone of C. pomonella. Such a differential phenomenon was not verified for the kdr-resistant insects, which exhibited a similar response to both the sex pheromone and the kairomonal attractant in apple orchards. Considering the widespread distribution of metabolic resistance in European populations of C. pomonella and the enhanced behavioral response to Et-E,Z-DD in resistant moths, the development of control measures based on this kairomonal compound would be of great interest for the management of insecticide resistance in this species.

Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery

The relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential.

Predictors for dioxin accumulation in residents living in Da Nang and Bien Hoa, Vietnam, many years after Agent Orange use

Agent Orange (AO) was the main defoliant used by the US in Vietnam from 1961 to 1971; AO was contaminated with dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD). Three major dioxin “hot spots” remain from previous AO storage and use at former US bases at Bien Hoa, Da Nang, and Phu Cat, posing potential health risks for Vietnamese living on or near these hot spots. We evaluated potential risk factors contributing to serum TCDD levels in Vietnamese residents at and near contaminated sites in Da Nang and Bien Hoa, Vietnam. We used multiple linear regression to analyze possible associations of blood dioxin concentrations with demographic, socioeconomic, lifestyle, and dietary risk factors for residents living on or near these hot spots. For the Da Nang study, fish farming on the site, living on property flooded from monsoon rains, and age were among the factors showing significant positive associations with serum TCDD concentrations. For the Bien Hoa study, fish farmers working at this site and their immediate family members had significantly higher serum TCDD concentrations. Our results suggest that water-related activities, especially fish-farming, at the hot spots increased the risk of exposure to dioxin.

Masting is uncommon in trees that depend on mutualist dispersers in the context of global climate and fertility gradients

The benefits of masting (volatile, quasi-synchronous seed production at lagged intervals) include satiation of seed predators, but these benefits come with a cost to mutualist pollen and seed dispersers. If the evolution of masting represents a balance between these benefits and costs, we expect mast avoidance in species that are heavily reliant on mutualist dispersers. These effects play out in the context of variable climate and site fertility among species that vary widely in nutrient demand. Meta-analyses of published data have focused on variation at the population scale, thus omitting periodicity within trees and synchronicity between trees. From raw data on 12 million tree-years worldwide, we quantified three components of masting that have not previously been analysed together: (i) volatility, defined as the frequency-weighted year-to-year variation; (ii) periodicity, representing the lag between high-seed years; and (iii) synchronicity, indicating the tree-to-tree correlation. Results show that mast avoidance (low volatility and low synchronicity) by species dependent on mutualist dispersers explains more variation than any other effect. Nutrient-demanding species have low volatility, and species that are most common on nutrient-rich and warm/wet sites exhibit short periods. The prevalence of masting in cold/dry sites coincides with climatic conditions where dependence on vertebrate dispersers is less common than in the wet tropics. Mutualist dispersers neutralize the benefits of masting for predator satiation, further balancing the effects of climate, site fertility and nutrient demands.

Bark and Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae) Diversity in Natural and Plantation Forests in Ecuador

The Scolytinae is highly diversified in tropical forests, but richness and abundance patterns within most Ecuadorian forest habitat types are not yet characterized. In this study, we assessed patterns of variation in Scolytinae richness, abundance, and species composition in a primary and a secondary natural forest, and a commercial balsa plantation in Ecuador. We conducted a 1-yr survey of Scolytinae communities with baited traps and measured associated environmental variables. In total, 18,169 Scolytinae individuals were captured and comprised 85 species, 16 genera, and six tribes. In the natural forests, main indicator species were Xylosandrus morigerus, Xyleborus affinis, Xyleborus sp.02, and Corthylus sp.01, whereas all species of Hypothenemus were indicator species in the balsa plantation. The exotic Premnobius cavipennis (Ipini), Xylosandrus compactus, and Xylosandrus morigerus were indicator species for the natural forests. We provide evidence that commercial balsa plantations provide abundant favorable resources for native and exotic scolytines in Ecuador, and that scolytine communities in natural forest and in plantations are more likely to differ in their species composition than in their cumulated species richness. In all habitats, species composition, abundance, and species richness showed temporal patterns of variation that coincided with seasonal variations in climatic conditions, with highest records during the coldest and driest months in the primary forest and the balsa plantation. We provide new knowledge on the native Ecuadorian scolytine fauna and a foundation for the monitoring for potential scolytine pest species of natural and planted tropical forest ecosystems.

Modelling the interactions between phenology and insecticide resistance genes in the codling moth Cydia pomonella

In the codling moth Cydia pomonella (L), insecticide resistance genes have been associated with pleiotropic effects affecting phenology. In this paper, we investigated whether an increase in the frequency of insecticide resistance in field populations of C pomonella was likely to entail significant divergences in the temporal occurrence of both susceptible and insecticide-resistant individuals. For this purpose, we built a phenological model that provided suitable predictions of the distinct and diverging seasonal evolutions of populations of a susceptible and two insecticide-resistant (at two and three loci) homozygous genotypes of C pomonella. Model simulations for each genotype were further compared with pheromone trap catches recorded in a field insecticide-treated population over an 8-year period (from 1992 to 2000), which reflected the progressive annual increase in the frequency of resistance in southeastern France. We found a significant delay in field adult emergence relative to those predicted by the homozygous susceptible model, and the magnitude of such a delay was positively correlated with increasing frequencies of insecticide resistance in the sampled field population of C pomonella. Adult emergence predicted in the theoretical population that was homozygous for resistance at two loci converged with those recorded in the field during the investigated 8-year period. This suggested that the pleiotropic effects of resistance were likely to result in a significant phenological segregation of insecticide-resistant alleles in the field. The results of this study emphasized the potential for pest populations exposed to chemical selection to evolve qualitatively with respect to phenology. This may raise critical questions regarding the use of phenological modelling as a forecasting tool for appropriate resistance management strategies that would take into account the diverging seasonal evolutions of both insecticide resistance and susceptibility.

Effects of apple orchard management strategies on the great tit (Parus major) in southeastern France

The impact of conventional, organic, and integrated pest management (IPM) strategies of apple orchards on the reproduction of the great tit Parus major was investigated during a three-year period in southeastern France. The colonization process, egg-laying dates, clutch sizes, and fledging success were similar among pairs of P. major nesting in orchards conducted under the three studied management strategies. However, the mean number of young produced per ha (orchard productivity) was significantly higher in organic orchards than in both conventional and IPM orchards. Such divergences between both fledging success and orchard productivity primarily resulted from higher densities of P. major nesting pairs, but also from lower rates of nest abandonment during incubation in organic orchards. We suggest that intensive pesticide use under both IPM and conventional managements may have resulted in a substantial reduction in insect prey availability that enhanced intraspecific competition, which then led to failure in reproduction in pairs with low competitive ability. Our results highlight the relevance of P. major in assessing the environmental impact of apple orchard management strategies.

Host-Parasite Interactions from the Inside: Plant Reproductive Ontogeny Drives Specialization in Parasitic Insects

Host plant interactions are likely key drivers of evolutionary processes involved in the diversification of phytophagous insects. Granivory has received substantial attention for its crucial role in shaping the interaction between plants and their seed parasites, but fine-scale mechanisms explaining the role of host plant reproductive biology on specialization of seed parasites remain poorly described. In a comparative approach using plant histological techniques, we tested the hypotheses that different seed parasite species synchronize their life cycles to specific stages in seed development, and that the stage they target depends on major differences in seed development programs. In a pinaceous system, seed storage products are initiated before ovule fertilization and the wasps target the ovule’s nucellus during megagametogenesis, a stage at which larvae may benefit from the by-products derived from both secreting cells and dying nucellar cells. In a cupressaceous system, oviposition activity peaks later, during embryogenesis, and the wasps target the ovule’s megagametophyte where larvae may benefit from cell disintegration during embryogenesis. Our cytohistological approach shows for the first time how, despite divergent oviposition targets, different parasite species share a common strategy that consists of first competing for nutrients with developing plant structures, and then consuming these developed structures to complete their development. Our results support the prediction that seed developmental program is an axis for specialization in seed parasites, and that it could be an important parameter in models of their ecological and taxonomic divergence. This study provides the basis for further investigating the possibility of the link between plant ontogeny and pre-dispersal seed parasitism.