Pre-invasion history and demography shape the genetic variation in the insecticide resistance-related acetylcholinesterase 2 gene in the invasive Colorado potato beetle

A high heterozygosity genome assembly of Aedes albopictus enables the discovery of the association of PGANT3 with blood-feeding behavior

The Asian tiger mosquito, Aedes albopictus, is a global invasive species, notorious for its role in transmitting dangerous human arboviruses such as dengue and Chikungunya. Although hematophagous behavior is repulsive, it is an effective strategy for mosquitoes like Aedes albopictus to transmit viruses, posing a significant risk to human health. However, the fragmented nature of the Ae. albopictus genome assembly has been a significant challenge, hindering in-depth biological and genetic studies of this mosquito. In this research, we have harnessed a variety of technologies and implemented a novel strategy to create a significantly improved genome assembly for Ae. albopictus, designated as AealbF3. This assembly boasts a completeness rate of up to 98.1%, and the duplication rate has been minimized to 1.2%. Furthermore, the fragmented contigs or scaffolds of AealbF3 have been organized into three distinct chromosomes, an arrangement corroborated through syntenic plot analysis, which compared the genetic structure of Ae. albopictus with that of Ae. aegypti. Additionally, the study has revealed a phylogenetic relationship suggesting that the PGANT3 gene is implicated in the hematophagous behavior of Ae. albopictus. This involvement was preliminarily substantiated through RNA interference (RNAi) techniques and behavioral experiment. In summary, the AealbF3 genome assembly will facilitate new biological insights and intervention strategies for combating this formidable vector of disease. The innovative assembly process employed in this study could also serve as a valuable template for the assembly of genomes in other insects characterized by high levels of heterozygosity.

Evidence of active oviposition avoidance to systemically applied imidacloprid in the Colorado potato beetle

Agricultural pests can develop behavioral resistance to insecticides by choosing to feed or oviposit on insecticide-free hosts. As young larvae have relatively low mobility, oviposition preferences from female adults may play a critical role in shaping the evolutionary trajectory of pest populations. While oviposition avoidance of insecticide-treated hosts was found in different agriculture pests, it remains unclear whether female adults actively choose to occupy insecticide-free hosts. To address this question, we investigated feeding and oviposition preferences between imidacloprid-treated and imidacloprid-free plants in the Colorado potato beetle, Leptinotarsa decemlineata Say, a major potato pest. We performed behavioral choice assays on two strains that differed in both fecundity and insecticide resistance. We found that one strain preferred to feed on the insecticide-free plants and that this preference is not innate. Meanwhile, the other strain chose plants for feeding and oviposition randomly. Further analyses of the moving patterns of the beetles suggested that the oviposition preference in the first strain is likely due to active learning.

Fungicides modify pest insect fitness depending on their genotype and population

Fungicides are the most sold pesticide group, with an 8% increase in sales in Europe within the last decade. While adverse short-term fungicide effects on non-target insect species have been reported, the long-term effects and their impact on fitness are unclear. As the effects may depend on both the fungicide and the genetic background of the species, we investigated the effects of the commonly used fungicide, fluazinam, on the Colorado potato beetle's life history traits, and whether the effects were dependent on a previously characterized insecticide resistance mutation (S291G in acetylcholinesterase-2 gene) in different populations. Our findings show that fungicide exposure can have both negative and positive, long-lasting effects on beetles, depending on the parental insecticide resistance status and population. In the Belchow population, individuals carrying resistance mutation had higher survival, but they produced offspring with lower egg-hatching rates. While, in the Vermont population, fungicide exposure increased the body mass and offspring quality in the beetles carrying resistance mutation but did not affect the beetles' survival. Our results suggest that commonly used fungicides can have both negative and positive effects on pest insects' life-history, however, their impact may differ depending on the population and parental genetic background.

The effects of short-term glyphosate-based herbicide exposure on insect gene expression profiles

Glyphosate-based herbicides (GBHs) are the most frequently used herbicides worldwide. The use of GBHs is intended to tackle weeds, but GBHs have been shown to affect the life-history traits and antioxidant defense system of invertebrates found in agroecosystems. Thus far, the effects of GBHs on detoxification pathways among invertebrates have not been sufficiently investigated. We performed two different experiments-1) the direct pure glyphosate and GBH treatment, and 2) the indirect GBH experiment via food-to examine the possible effects of environmentally relevant GBH levels on the survival of the Colorado potato beetle (Leptinotarsa decemlineata) and the expression profiles of their detoxification genes. As candidate genes, we selected four cytochrome P450 (CYP), three glutathione-S-transferase (GST), and two acetylcholinesterase (AChE) genes that are known to be related to metabolic or target-site resistances in insects. We showed that environmentally relevant levels of pure glyphosate and GBH increased the probability for higher mortality in the Colorado potato beetle larvae in the direct experiment, but not in the indirect experiment. The GBHs or glyphosate did not affect the expression profiles of the studied CYP, GST, or AChE genes; however, we found a large family-level variation in expression profiles in both the direct and indirect treatment experiments. These results suggest that the genes selected for this study may not be the ones expressed in response to glyphosate or GBHs. It is also possible that the relatively short exposure time did not affect gene expression profiles, or the response may have already occurred at a shorter exposure time. Our results show that glyphosate products may affect the survival of the herbivorous insect already at lower levels, depending on their sensitivity to pesticides.

Sequence variation and regulatory variation in acetylcholinesterase genes contribute to insecticide resistance in different populations of Leptinotarsa decemlineata

Although insect herbivores are known to evolve resistance to insecticides through multiple genetic mechanisms, resistance in individual species has been assumed to follow the same mechanism. While both mutations in the target site insensitivity and increased amplification are known to contribute to insecticide resistance, little is known about the degree to which geographic populations of the same species differ at the target site in a response to insecticides. We tested structural (e.g., mutation profiles) and regulatory (e.g., the gene expression of Ldace1 and Ldace2, AChE activity) differences between two populations (Vermont, USA and Belchow, Poland) of the Colorado potato beetle, Leptinotarsa decemlineata in their resistance to two commonly used groups of insecticides, organophosphates, and carbamates. We established that Vermont beetles were more resistant to azinphos-methyl and carbaryl insecticides than Belchow beetles, despite a similar frequency of resistance-associated alleles (i.e., S291G) in the Ldace2 gene. However, the Vermont population had two additional amino acid replacements (G192S and F402Y) in the Ldace1 gene, which were absent in the Belchow population. Moreover, the Vermont population showed higher expression of Ldace1 and was less sensitive to AChE inhibition by azinphos-methyl oxon than the Belchow population. Therefore, the two populations have evolved different genetic mechanisms to adapt to organophosphate and carbamate insecticides.

Glyphosate-based herbicide has soil-mediated effects on potato glycoalkaloids and oxidative status of a potato pest

Glyphosate is the most used herbicide worldwide, targeting physiological pathways in plants. Recent studies have shown that glyphosate can also cause toxic effects in animals. We investigated the glyphosate-based herbicide (GBH)-induced changes in potato (Solanum tuberosum) plant chemistry and the effects of a GBH on the survival rate and oxidative status of the Colorado potato beetle (Leptinotarsa decemlineata). The beetles were reared on potato plants grown in pots containing soil treated with a GBH (Roundup Gold, 450 g/l) or untreated soil (water control). The 2nd instar larvae were introduced to the potato plants and then collected in 2 phases: as 4th instar larvae and as adults. The main glycoalkaloids of the potato plants, α-solanine and α-chaconine, were measured twice during the experiment. The α-solanine was reduced in potato plants grown in GBH-treated soil, which can be detrimental to plant defenses against herbivores. GBH treatment had no effect on the survival rate or body mass of the larvae or the adult beetles. In the larvae, total glutathione (tGSH) concentration and the enzyme activity of catalase (CAT), superoxide dismutase, and glutathione-S-transferase were increased in the GBH treatment group. In the adult beetles, CAT activity and tGSH levels were affected by the interactive effect of GBH treatment and the body mass. To conclude, environmentally relevant concentrations of a GBH can affect the potato plant's glycoalkaloid concentrations, but are not likely to directly affect the survival rate of the Colorado potato beetle, but instead, modify the antioxidant defense of the beetles via diet.

Chemodiversity, chemotaxonomy and chemoecology of Amaryllidaceae alkaloids

The Amaryllidaceae alkaloids are a distinctive chemotaxonomic feature of the subfamily Amaryllidoideae of the family Amaryllidaceae, which consists of 59 genera and >800 species distributed primarily in tropical and subtropical areas. Since the first isolation, ca. 140 ago, >600 structurally diverse Amaryllidaceae alkaloids have been reported from ca. 350 species (44% of all species in the subfamily). A few have been found in other plant families, but the majority are unique to the Amaryllidoideae. These alkaloids have attracted considerable research interest due to their wide range of biological and pharmacological activities, which have been extensively reviewed. In this chapter we provide a review of the 636 structures of isolated or tentatively identified alkaloids from plants of the Amaryllidoideae and their classification into 42 skeleton types, as well as a discussion on their distribution, and chemotaxonomical and chemoecological aspects.

Prolonged diapause has sex-specific fertility and fitness costs

Diapause in seasonal environments allows insects to survive adverse seasons. However, individuals can sometimes enter a prolonged diapause for more than a year, and also skip favourable seasons, which can bring additional costs through e.g. loss of metabolic resources. At the same time, prolonged diapause can be beneficial if it allows individuals to have a risk-spreading strategy to skip potentially suboptimal breeding seasons. We studied if prolonged diapause (2-year diapause) negatively affects the fertility and fitness of female and male Colorado potato beetles (Leptinotarsa decemlineata) compared to control (1-year diapause) beetles. We also tested the parental effects on the subsequent chemical stress tolerance of their offspring. We found that prolonged diapause carried fertility costs only for females who were less fertile than the control females. However, no differences in fertility were observed in males. Furthermore, prolonged diapause in females resulted in offspring with lower larvae-to-adult survival even though these offspring had accelerated development times. In contrast, paternal diapause duration had no effects on their offspring larvae-to adult survival, but prolonged diapause males sired offspring with slower development times than control males. Perhaps to compensate the costs related to prolonged diapause both older parents produced or sired offspring with higher body mass than control parents. Despite the differences in emergence mass, parental diapause duration did not affect offspring insecticide stress tolerance. The difference between females and males most likely results from the observed differences in prolonged diapause females’ capacity to fight against cellular oxidative damage which was poorer compared to the control females. Even though prolonged diapause allows individuals to have a risk-spreading strategy it carries sex-specific fertility and fitness costs indicating that selection could favour this in males but not in females.

Can Indirect Herbicide Exposure Modify the Response of the Colorado Potato Beetle to an Organophosphate Insecticide?

Organisms live in complex multivariate environments. In agroecosystems, this complexity is often human-induced as pest individuals can be exposed to many xenobiotics simultaneously. Predicting the effects of multiple stressors can be problematic, as two or more stressors can have interactive effects. Our objective was to investigate whether indirect glyphosate-based herbicide (GBH) exposure of the host plant has interactive effects in combination with an insecticide (azinphos-methyl) on an invasive pest Colorado potato beetle (Leptinotarsa decemlineata Say). We tested the effects of GBH and insecticide on the survival, insecticide target genes expression (acetylcholinesterase genes) and oxidative status biomarkers (glutathione S-transferase [GST], glucose-6-phosphate dehydrogenase [G6PDH], glutathione reductase homolog [GR], glutathione peroxidase homolog [GPx], total glutathione [totGSH], glutathione reduced-oxidized [GSH: GSSG], catalase [CAT], superoxide dismutase [SOD], lipid hydroperoxides). We found that exposure to indirect GBH has no single or interactive effects in combination with the insecticide on larval survival. However, prior exposure to GBH inhibits Ldace1 gene expression by 0.55-fold, which is the target site for the organophosphate and carbamate insecticides. This difference disappears when individuals are exposed to both GBH and insecticide, suggesting an antagonistic effect. On the other hand, oxidative status biomarker scores (PCAs of GPx, GR, and CAT) were decreased when exposed to both stressors, indicating a synergistic effect. Overall, we found that indirect GBH exposure can have both antagonistic and synergistic effects in combination with an insecticide, which should be considered when aiming for an ecologically relevant risk assessment of multiple human-induced stressors.

Sublethal Pyrethroid Insecticide Exposure Carries Positive Fitness Effects Over Generations in a Pest Insect

Stress tolerance and adaptation to stress are known to facilitate species invasions. Many invasive species are also pests and insecticides are used to control them, which could shape their overall tolerance to stress. It is well-known that heavy insecticide usage leads to selection of resistant genotypes but less is known about potential effects of mild sublethal insecticide usage. We studied whether stressful, sublethal pyrethroid insecticide exposure has within-generational and/or maternal transgenerational effects on fitness-related traits in the Colorado potato beetle (Leptinotarsa decemlineata) and whether maternal insecticide exposure affects insecticide tolerance of offspring. Sublethal insecticide stress exposure had positive within-and transgenerational effects. Insecticide-stressed larvae had higher adult survival and higher adult body mass than those not exposed to stress. Furthermore, offspring whose mothers were exposed to insecticide stress had higher larval and pupal survival and were heavier as adults (only females) than those descending from control mothers. Maternal insecticide stress did not explain differences in lipid content of the offspring. To conclude, stressful insecticide exposure has positive transgenerational fitness effects in the offspring. Therefore, unsuccessful insecticide control of invasive pest species may lead to undesired side effects since survival and higher body mass are known to facilitate population growth and invasion success.

Effects of a glyphosate-based herbicide on survival and oxidative status of a non-target herbivore, the Colorado potato beetle (Leptinotarsa decemlineata)

Glyphosate is the globally most used herbicide against a wide range of weeds. Glyphosate has been considered safe to animals as it mainly targets physiological pathways in plants. However, recent toxicological studies have revealed that glyphosate can cause various toxic effects also on animals. In this study, we investigated the direct toxic effects of a glyphosate-based herbicide (GBH, Roundup® Bio) on 1) survival and 2) oxidative status of a non-target herbivore by using Colorado potato beetles (Leptinotarsa decemlineata), originating from Poland and USA, as model species. Larvae were randomly divided into three groups: 1) high concentration (100% Roundup Bio, 360 g/l), 2) low concentration (1.5% Roundup Bio) and 3) control group (water). Larvae were exposed to Roundup for different time periods: 2 h, 24 h, 48 h, 72 h and 96 h. Larval survival decreased in the group treated with high concentration of GBH compared to controls, whereas the low concentration group did not differ from the control group. GBH treatment had no association with oxidative status biomarkers (i.e. catalase, superoxide dismutase, glutathione-S-transferase, glutathione and glutathione related enzymes), but increased lipid hydroperoxide levels after 2 h exposure, suggesting increased oxidative damage soon after the exposure. Larvae of different origin also differed in their oxidative status, indicating population-dependent differences in antioxidant defence system. Environmentally relevant concentrations of GBH are not likely to affect larval survival, but high concentrations can reduce survival and increase oxidative damage of non-target herbivores. Also, populations of different origin and pesticide usage history can differ in their tolerance to GBH.

Origin of Pest Lineages of the Colorado Potato Beetle (Coleoptera: Chrysomelidae)

Colorado potato beetle (Leptinotarsa decemlineata Say [Coleoptera: Chrysomelidae]) is a pest of potato throughout the Northern Hemisphere, but little is known about the beetle's origins as a pest. We sampled the beetle from uncultivated Solanum host plants in Mexico, and from pest and non-pest populations in the United States and used mitochondrial DNA and nuclear loci to examine three hypotheses on the origin of the pest lineages: 1) the pest beetles originated from Mexican populations, 2) they descended from hybridization between previously divergent populations, or 3) they descended from populations that are native to the Plains states in the United States. Mitochondrial haplotypes of non-pest populations from Mexico and Arizona differed substantially from beetles collected from the southern plains and potato fields in the United States, indicating that beetles from Mexico and Arizona did not contribute to founding the pest lineages. Similar results were observed for AFLP and microsatellite data . In contrast, non-pest populations from the states of Colorado, Kansas, Nebraska, New Mexico, and Texas were genetically similar to U.S. pest populations, indicating that they contributed to the founding of the pest lineages. Most of the pest populations do not show a significant reduction in genetic diversity compared to the plains populations in the United States. We conclude that genetically heterogeneous beetle populations expanded onto potato from native Solanum hosts. This mode of host range expansion may have contributed to the abundant genetic diversity of contemporary populations, perhaps contributing to the rapid evolution of climate tolerance, host range, and insecticide resistance.

Role of dispersal in resistance evolution and spread

Gene flow via immigration affects rate of evolution of resistance to a pest management tactic, while emigration from a resistant population can spread resistance alleles spatially. Whether resistance detected across the landscape reflects ongoing de novo evolution in different hotspots or spread from a single focal population can determine the most effective mitigation strategy. Pest dispersal dynamics determine the spatio-temporal scale at which mitigation tactics must be applied to contain or reverse resistance in an area. Independent evolution of resistance in different populations appears common but not universal. Conversely, spatial spread appears to be almost inevitable. However, rate and scale of spread depends largely on dispersal dynamics and interplay with factors such as fitness costs, spatially variable selection pressure and whether resistance alleles are spreading through an established population or being carried by populations colonizing new territory.

Spatial and Temporal Potato Intensification Drives Insecticide Resistance in the Specialist Herbivore, Leptinotarsa decemlineata

Landscape-scale intensification of individual crops and pesticide use that is associated with this intensification is an emerging, environmental problem that is expected to have unequal effects on pests with different lifecycles, host ranges, and dispersal abilities. We investigate if intensification of a single crop in an agroecosystem has a direct effect on insecticide resistance in a specialist insect herbivore. Using a major potato pest, Leptinotarsa decemlineata, we measured imidacloprid (neonicotinoid) resistance in populations across a spatiotemporal crop production gradient where potato production has increased in Michigan and Wisconsin, USA. We found that concurrent estimates of area and temporal frequency of potato production better described patterns of imidacloprid resistance among L. decemlineata populations than general measures of agricultural production (% cropland, landscape diversity). This study defines the effects individual crop rotation patterns can have on specialist herbivore insecticide resistance in an agroecosystem context, and how impacts of intensive production can be estimated with general estimates of insecticide use. Our results provide empirical evidence that variation in the intensity of neonicotinoid-treated potato in an agricultural landscape can have unequal impacts on L. decemlineata insecticide insensitivity, a process that can lead to resistance and locally intensive insecticide use. Our study provides a novel approach applicable in other agricultural systems to estimate impacts of crop rotation, increased pesticide dependence, insecticide resistance, and external costs of pest management practices on ecosystem health.

Incongruent nuclear and mitochondrial genetic structure of new world screwworm fly populations due to positive selection of mutations associated with dimethyl- and diethyl-organophosphates resistance

Livestock production is an important economic activity in Brazil, which has been suffering significant losses due to the impact of parasites. The New World screwworm (NWS) fly, Cochliomyia hominivorax, is an ectoparasite and one of the most important myiasis-causing flies endemic to the Americas. The geographic distribution of NWS has been reduced after the implementation of the Sterile Insect Technique (SIT), being eradicated in North America and part of Central America. In South America, C. hominivorax is controlled by chemical insecticides, although indiscriminate use can cause selection of resistant individuals. Previous studies have associated the Gly137Asp and Trp251Leu mutations in the active site of carboxylesterase E3 to resistance of diethyl and dimethyl-organophosphates insecticides, respectively. Here, we have sequenced a fragment of the carboxylesterase E3 gene (ChαE7), comprising part of intron iII, exon eIII, intron iIII and part of exon eIV, and three mitochondrial gene sequences (CR, COI and COII), of NWS flies from 21 locations in South America. These markers were used for population structure analyses and the ChαE7 gene was also investigated to gain insight into the selective pressures that have shaped its evolution. Analysis of molecular variance (AMOVA) and pairwise FST analysis indicated an increased genetic structure between locations in the ChαE7 compared to the concatenated mitochondrial genes. Discriminant analysis of principal components (DAPC) and spatial analysis of molecular variance (SAMOVA) indicated different degrees of genetic structure for all markers, in agreement with the AMOVA results, but with low correlation to geographic data. The NWS fly is considered a panmitic species based on mitochondrial data, while it is structured into three groups considering the ChαE7 gene. A negative association between the two mutations related to organophosphate resistance and Fay & Wu’s H significant negative values for the exons, suggest that these mutations evolved under positive selection.

The Red Queen in a potato field: integrated pest management versus chemical dependency in Colorado potato beetle control

Originally designed to reconcile insecticide applications with biological control, the concept of integrated pest management (IPM) developed into the systems-based judicious and coordinated use of multiple control techniques aimed at reducing pest damage to economically tolerable levels. Chemical control, with scheduled treatments, was the starting point for most management systems in the 1950s. Although chemical control is philosophically compatible with IPM practices as a whole, reduction in pesticide use has been historically one of the main goals of IPM practitioners. In the absence of IPM, excessive reliance on pesticides has led to repeated control failures due to the evolution of resistance by pest populations. This creates the need for constant replacement of failed chemicals with new compounds, known as the 'insecticide treadmill'. In evolutionary biology, a similar phenomenon is known as the Red Queen principle - continuing change is needed for a population to persevere because its competitors undergo constant evolutionary adaptation. The Colorado potato beetle, Leptinotarsa decemlineata (Say), is an insect defoliator of potatoes that is notorious for its ability to develop insecticide resistance. In the present article, a review is given of four case studies from across the United States to demonstrate the importance of using IPM for sustainable management of a highly adaptable insect pest. Excessive reliance on often indiscriminate insecticide applications and inadequate use of alternative control methods, such as crop rotation, appear to expedite evolution of insecticide resistance in its populations. Resistance to IPM would involve synchronized adaptations to multiple unfavorable factors, requiring statistically unlikely genetic changes. Therefore, integrating different techniques is likely to reduce the need for constant replacement of failed chemicals with new ones.

Agroecosystems shape population genetic structure of the greenhouse whitefly in Northern and Southern Europe

BACKGROUND

To predict further invasions of pests it is important to understand what factors contribute to the genetic structure of their populations. Cosmopolitan pest species are ideal for studying how different agroecosystems affect population genetic structure within a species at different climatic extremes. We undertook the first population genetic study of the greenhouse whitefly (Trialeurodes vaporariorum), a cosmopolitan invasive herbivore, and examined the genetic structure of this species in Northern and Southern Europe. In Finland, cold temperatures limit whiteflies to greenhouses and prevent them from overwintering in nature, and in Greece, milder temperatures allow whiteflies to inhabit both fields and greenhouses year round, providing a greater potential for connectivity among populations. Using nine microsatellite markers, we genotyped 1274 T. vaporariorum females collected from 18 greenhouses in Finland and eight greenhouses as well as eight fields in Greece.

RESULTS

Populations from Finland were less diverse than those from Greece, suggesting that Greek populations are larger and subjected to fewer bottlenecks. Moreover, there was significant population genetic structure in both countries that was explained by different factors. Habitat (field vs. greenhouse) together with longitude explained genetic structure in Greece, whereas in Finland, genetic structure was explained by host plant species. Furthermore, there was no temporal genetic structure among populations in Finland, suggesting that year-round populations are able to persist in greenhouses.

CONCLUSIONS

Taken together our results show that greenhouse agroecosystems can limit gene flow among populations in both climate zones. Fragmented populations in greenhouses could allow for efficient pest management. However, pest persistence in both climate zones, coupled with increasing opportunities for naturalization in temperate latitudes due to climate change, highlight challenges for the management of cosmopolitan pests in Northern and Southern Europe.

Northward range expansion requires synchronization of both overwintering behaviour and physiology with photoperiod in the invasive Colorado potato beetle (Leptinotarsa decemlineata)

Photoperiodic phenological adaptations are prevalent in many organisms living in seasonal environments. As both photoperiod and growth season length change with latitude, species undergoing latitudinal range expansion often need to synchronize their life cycle with a changing photoperiod and growth season length. Since adaptive synchronization often involves a large number of time-consuming genetic changes, behavioural plasticity might be a faster way to adjust to novel conditions. We compared behavioural and physiological traits in overwintering (diapause) preparation in three latitudinally different European Colorado potato beetle (Leptinotarsa decemlineata) populations reared under two photoperiods. Our aim was to study whether behavioural plasticity could play a role in rapid range expansion into seasonal environments. Our results show that while burrowing into the soil occurred in the southernmost studied population also under a non-diapause-inducing long photoperiod, the storage lipid content of these beetles was very low compared to the northern populations. However, similar behavioural plasticity was not found in the northern populations. Furthermore, the strongest suppression of energy metabolism was seen in pre-diapause beetles from the northernmost population. These results could indicate accelerated diapause preparation and possibly energetic adjustments due to temporal constraints imposed by a shorter, northern, growth season. Our results indicate that behavioural plasticity in burrowing may have facilitated initial range expansion of L. decemlineata in Europe. However, long-term persistence at high latitudes has required synchronization of burrowing behaviour with physiological traits. The results underline that eco-physiological life-history traits of insects, such as diapause, should be included in studies on range expansion.

Global distribution and origin of target site insecticide resistance mutations in Tetranychus urticae

The control of Tetranychus urticae, a worldwide agricultural pest, is largely dependent on pesticides. However, their efficacy is often compromised by the development of resistance. Recent molecular studies identified a number of target site resistance mutations, such as G119S, A201S, T280A, G328A, F331W in the acetylcholinesterase gene, L1024V, A1215D, F1538I in the voltage-gated sodium channel gene, G314D and G326E in glutamate-gated chloride channel genes, G126S, I136T, S141F, D161G, P262T in the cytochrome b and the I1017F in the chitin synthase 1 gene. We examined their distribution, by sequencing the relevant gene fragments in a large number of T. urticae collections from a wide geographic range. Our study revealed that most of the resistance mutations are spread worldwide, with remarkably variable frequencies. Furthermore, we analyzed the variability of the ace locus, which has been subjected to longer periods of selection pressure historically, to investigate the evolutionary origin of ace resistant alleles and determine whether they resulted from single or multiple mutation events. By sequencing a 1540 bp ace fragment, encompassing the resistance mutations and downstream introns in 139 T. urticae individuals from 27 countries, we identified 6 susceptible and 31 resistant alleles which have arisen from at least three independent mutation events. The frequency and distribution of these ace haplotypes varied geographically, suggesting an interplay between different mutational events, gene flow and local selection.

Colorado potato beetle (Coleoptera) gut transcriptome analysis: expression of RNA interference-related genes

In the search for new methods of pest control, the potential of RNA interference (RNAi) is being explored. Because the gut is the first barrier for the uptake of double-stranded (ds)RNA, pyrosequencing of the gut transcriptome is a powerful tool for obtaining the necessary sequences for specific dsRNA-mediated pest control. In the present study, a dataset representing the gut transcriptome of the Colorado potato beetle (CPB; Leptinotarsa decemlineata) was generated and analysed for the presence of RNAi-related genes. Almost all selected genes that were implicated in silencing efficiency at different levels in the RNAi pathway (core machinery, associated intracellular factors, dsRNA uptake, antiviral RNAi, nucleases), which uses different types of small RNA (small interfering RNA, microRNA and piwi-RNA), were expressed in the CPB gut. Although the database is of lower quality, the majority of the RNAi genes are also found to be present in the gut transcriptome of the tobacco hornworm [TH; Manduca sexta (19 out of 35 genes analysed)]. The high quality of the CPB transcriptome database will lay the foundation for future gene expression and functional studies regarding the gut and RNAi.

Transitions between Andean and Amazonian centers of endemism in the radiation of some arboreal rodents

Background

The tropical Andes and Amazon are among the richest regions of endemism for mammals, and each has given rise to extensive in situ radiations. Various animal lineages have radiated ex situ after colonizing one of these regions from the other: Amazonian clades of dendrobatid frogs and passerine birds may have Andean ancestry, and transitions from the Amazon to Andes may be even more common. To examine biogeographic transitions between these regions, we investigated the evolutionary history of three clades of rodents in the family Echimyidae: bamboo rats (Dactylomys-Olallamys-Kannabateomys), spiny tree-rats (Mesomys-Lonchothrix), and brush-tailed rats (Isothrix). Each clade is distributed in both the Andes and Amazonia, and is more diverse in the lowlands. We used two mitochondrial (cyt-b and 12S) and three nuclear (GHR, vWF, and RAG1) markers to reconstruct their phylogenetic relationships. Tree topologies and ancestral geographic ranges were then used to determine whether Andean forms were basal to or derived from lowland radiations.

Results

Four biogeographic transitions are identified among the generic radiations. The bamboo rat clade unambiguously originated in the Amazon ca. 9 Ma, followed by either one early transition to the Andes (Olallamys) and a later move to the Amazon (Dactylomys), or two later shifts to the Andes (one in each genus). The Andean species of both Dactylomys and Isothrix are sister to their lowland species, raising the possibility that highland forms colonized the Amazon Basin. However, uncertainty in their reconstructed ancestral ranges obscures the origin of these transitions. The lone Andean species of Mesomys is confidently nested within the lowland radiation, thereby indicating an Amazon-to-Andes transition ca. 2 Ma.

Conclusions

Differences in the timing of these biogeographic transitions do not appear to explain the different polarities of these trees. Instead, even within the radiation of a single family, both Andean and Amazonian centers of endemism appear enriched by lineages that originated in the other region. Our survey of other South American lineages suggests a pattern of reciprocal exchange between these regions—among mammals, birds, amphibians, and insects we found no fewer than 87 transitions between the Andes and Amazon from Miocene-Pleistocene. Because no clear trend emerges between the timing and polarity of transitions, or in their relative frequency, we suggest that reciprocal exchange between tropical highland and lowland faunas in South America has been a continual process since ca. 12 Ma.

Towards a molecular understanding of the biosynthesis of amaryllidaceae alkaloids in support of their expanding medical use

The alkaloids characteristically produced by the subfamily Amaryllidoideae of the Amaryllidaceae, bulbous plant species that include well know genera such as Narcissus (daffodils) and Galanthus (snowdrops), are a source of new pharmaceutical compounds. Presently, only the Amaryllidaceae alkaloid galanthamine, an acetylcholinesterase inhibitor used to treat symptoms of Alzheimer's disease, is produced commercially as a drug from cultivated plants. However, several Amaryllidaceae alkaloids have shown great promise as anti-cancer drugs, but their further clinical development is restricted by their limited commercial availability. Amaryllidaceae species have a long history of cultivation and breeding as ornamental bulbs, and phytochemical research has focussed on the diversity in alkaloid content and composition. In contrast to the available pharmacological and phytochemical data, ecological, physiological and molecular aspects of the Amaryllidaceae and their alkaloids are much less explored and the identity of the alkaloid biosynthetic genes is presently unknown. An improved molecular understanding of Amaryllidaceae alkaloid biosynthesis would greatly benefit the rational design of breeding programs to produce cultivars optimised for the production of pharmaceutical compounds and enable biotechnology based approaches.