Showing papers in "Current opinion in insect science in 2015"

Bee nutrition and floral resource restoration

Abstract: Bee-population declines are linked to nutritional shortages caused by land-use intensification, which reduces diversity and abundance of host-plant species. Bees require nectar and pollen floral resources that provide necessary carbohydrates, proteins, lipids, and micronutrients for survival, reproduction, and resilience to stress. However, nectar and pollen nutritional quality varies widely among host-plant species, which in turn influences how bees forage to obtain their nutritionally appropriate diets. Unfortunately, we know little about the nutritional requirements of different bee species. Research must be conducted on bee species nutritional needs and host-plant species resource quality to develop diverse and nutritionally balanced plant communities. Restoring appropriate suites of plant species to landscapes can support diverse bee species populations and their associated pollination ecosystem services.

Xenobiotic detoxification pathways in honey bees

Abstract: Relative to most other insect genomes, the western honey bee Apis mellifera has a deficit of detoxification genes spanning Phase I (functionalization), II (conjugation) and III (excretion) gene families. Although honeybees do not display across-the-board greater sensitivity to pesticides, this deficit may render them vulnerable to synergistic interactions among xenobiotics. Diet quality, in terms of protein and phytochemical content, has a pronounced influence on tolerance of toxic compounds. Detoxification gene inventory reduction may reflect an evolutionary history of consuming relatively chemically benign nectar and pollen, as other apoid pollinators display comparable levels of cytochrome P450 gene reduction. Enzymatic detoxification in the eusocial A. mellifera may be complemented by behaviors comprising a 'social detoxification system,' including forager discrimination, dilution by pollen mixing, and colony food processing via microbial fermentation, that reduces the number or quantity of ingested chemicals requiring detoxification.

Honey bee colony losses and associated viruses

Abstract: Recent large-scale colony losses among managed Western honey bees (Apis mellifera) have alarmed researchers and apiculturists alike. Here, the existing correlative evidence provided by monitoring studies is reviewed which (i) identified members of the deformed wing virus and acute bee paralysis virus clades as lethal pathogens for entire colonies, and (ii) identified novel viruses whose impact on honey bee health remains elusive. Also discussed in this review is related evidence obtained via controlled experimental infection assays and RNAi approaches underscoring the damage inflicted by some of these viruses on individuals and colonies. The relevance of the ectoparasitic mite Varroa destructor acting as mechanical and biological virus vector for the enhanced virulence of certain viruses or mite selected virus strains is carefully considered.

Back to the future: the sterile insect technique against mosquito disease vectors.

Abstract: With the global burden of mosquito-borne diseases increasing, and some conventional vector control tools losing effectiveness, the sterile insect technique (SIT) is a potential new tool in the arsenal. Equipment and protocols have been developed and validated for efficient mass-rearing, irradiation and release of Aedines and Anophelines that could be useful for several control approaches. Assessment of male quality is becoming more sophisticated, and several groups are well advanced in pilot site selection and population surveillance. It will not be long before SIT feasibility has been evaluated in various settings. Until perfect sexing mechanisms exist, combination of Wolbachia-induced phenotypes, such as cytoplasmic incompatibility and pathogen interference, and irradiation may prove to be the safest solution for population suppression.

Clip-domain serine proteases as immune factors in insect hemolymph

Abstract: CLIP proteases are non-digestive serine proteases present in hemolymph of insects and other arthropods. They are composed of one or more amino-terminal clip domains followed by a linker sequence and a carboxyl-terminal S1A family serine protease domain. The genes for CLIP proteases have evolved as four clades (CLIPA, CLIPB, CLIPC, CLIPD), each present as multigene families in insect genomes. CLIP proteases in hemolymph function in innate immune responses. These include proteolytic activation of the cytokine Spatzle, to form an active Toll ligand leading to synthesis of antimicrobial peptides, and specific activation of prophenoloxidase, required for the melanization response. CLIP proteases act in cascade pathways. In the immune pathways that have been characterized, microbial surface molecules stimulate activation of an initiating modular serine protease, which then activates a CLIPC, which in turn activates a CLIPB. The active CLIPB then cleaves and activates an effector molecule (proSpatzle or prophenoloxidase). CLIPA proteins are pseudoproteases, lacking proteolytic activity, but some can function as regulators of the activity of other CLIP proteases and form high molecular weight immune complexes. A few three dimensional structures for CLIP proteases are now available for structure-function analysis of these immune factors, revealing structural features that may act in specific activation or in formation of immune complexes. The functions of most CLIP proteases are unknown, even in well studied insect species. It is very likely that additional proteins activated by CLIP proteases and acting in immunity remain to be discovered.

Molecular basis of juvenile hormone signaling.

Abstract: Despite important roles played by juvenile hormone (JH) in insects, the mechanisms underlying its action were until recently unknown. A breakthrough has been the demonstration that the bHLH-PAS protein Met is an intracellular receptor for JH. Binding of JH to Met triggers dimerization of Met with its partner protein Tai, and the resulting complex induces transcription of target genes. In addition, JH can potentiate this response by phosphorylating Met and Tai via cell membrane, second-messenger signaling. An important gene induced by the JH–Met–Tai complex is Kr-h1, which inhibits metamorphosis. Kr-h1 represses an ‘adult specifier’ gene E93. The action of this JH-activated pathway in maintaining the juvenile status is dispensable during early postembryonic development when larvae/nymphs lack competence to metamorphose.

Molecular mechanisms of insect adaptation to plant secondary compounds

Abstract: During feeding, herbivorous insects are exposed to an array of plant defensive compounds. In this review, we examine molecular mechanisms of insect adaptation to these toxic metabolites. We discuss both the importance of evolutionary variation of existing detoxification gene families, as well as the evolution of novel mechanisms through gene recruitment, neofunctionalization and horizontal gene transfer. The ability of insects to cope with the chemical diversity of their host plants and the different mechanisms that insects use to resist these toxins open new avenues for understanding fundamental aspects of insect-plant coevolutionary adaptation.

Nutrition, immunity and viral infections in honey bees.

Abstract: Viruses and other pathogens can spread rapidly in social insect colonies from close contacts among nestmates, food sharing and periods of confinement Here we discuss how honey bees decrease the risk of disease outbreaks by a combination of behaviors (social immunity) and individual immune function There is a relationship between the effectiveness of social and individual immunity and the nutritional state of the colony Parasitic Varroa mites undermine the relationship because they reduce nutrient levels, suppress individual immune function and transmit viruses Future research directions to better understand the dynamics of the nutrition-immunity relationship based on levels of stress, time of year and colony demographics are discussed

Genomics of the honey bee microbiome

Abstract: The guts of honey bee workers contain a distinctive community of bacterial species. They are microaerophilic or anaerobic, and were not clearly deliniated by earlier studies relying on laboratory culture of isolates under atmospheric oxygen levels. Recently, a more complete picture of the potential metabolism and functions of these bacteria has been possible, using genomic approaches based on metagenomic samples, as well as cultured isolates. Of these, most are host-restricted and are generally absent outside adult guts. These species include both Gram negative groups, such as Gilliamella apicola and Snodgrassella alvi, and Gram positive groups such as certain Lactobacillus and Bifidobacterium species. These gut bacterial species appear to have undergone long term coevolution with honey bee and, in some cases, bumble bee hosts. Prediction of gene functions from genome sequences suggests roles in nutrition, digestion, and potentially in defense against pathogens. In particular, genes for sugar utilization and carbohydrate breakdown are enriched in G. apicola and the Lactobacillus species.

RNA interference-mediated antiviral defense in insects

Abstract: Small interfering RNA (siRNA)-mediated RNA interference (RNAi) pathways are critical for the detection and inhibition of RNA virus replication in insects. Recent work has also implicated RNAi pathways in the establishment of persistent virus infections and in the control of DNA virus replication. Accumulating evidence suggests that diverse double-stranded RNAs produced by RNA and DNA viruses can trigger RNAi responses yet many viruses have evolved mechanisms to inhibit RNAi defenses. Therefore, an evolutionary arms race exists between host RNAi pathways and invading viral pathogens. Here we review recent advances in our knowledge of how insect RNAi pathways are elicited upon infection, the strategies used by viruses to counter these defenses, and discuss recent evidence implicating Piwi-interacting RNAs in antiviral defense.

Antiviral Defense Mechanisms in Honey Bees.

Abstract: Honey bees are significant pollinators of agricultural crops and other important plant species. High annual losses of honey bee colonies in North America and in some parts of Europe have profound ecological and economic implications. Colony losses have been attributed to multiple factors including RNA viruses, thus understanding bee antiviral defense mechanisms may result in the development of strategies that mitigate colony losses. Honey bee antiviral defense mechanisms include RNA-interference, pathogen-associated molecular pattern (PAMP) triggered signal transduction cascades, and reactive oxygen species generation. However, the relative importance of these and other pathways is largely uncharacterized. Herein we review the current understanding of honey bee antiviral defense mechanisms and suggest important avenues for future investigation.

Overwintering honey bees: biology and management

Abstract: In temperate climates, honey bees (Apis mellifera) survive the winter by entering a distinct physiological and behavioral state. In recent years, beekeepers are reporting unsustainably high colony losses during the winter, which have been linked to parasitization by Varroa mites, virus infections, geographic location, and variation across honey bee genotypes. Here, we review literature on environmental, physiological, and social factors regulating entrance, maintenance, and exit from the overwintering state in honey bees in temperate regions and develop a testable model to explain how multiple factors may be acting synergistically to regulate this complex transition. We also review existing knowledge of the factors affecting overwintering survival in honey bees and providing suggestions to beekeepers aiming to improve their colonies’ overwintering success.

Pollinator conservation - The difference between managing for pollination services and preserving pollinator diversity

Abstract: Our review looks at pollinator conservation and highlights the differences in approach between managing for pollination services and preserving pollinator diversity. We argue that ecosystem service management does not equal biodiversity conservation, and that maintaining species diversity is crucial in providing ecosystem resilience in the face of future environmental change. Management and policy measures therefore need to focus on species not just in human dominated landscapes but need to benefit wider diversity of species including those in specialised habitats. We argue that only by adopting a holistic ecosystem approach we can ensure the conservation and sustainable use of biodiversity and ecosystem services in the long-term.

Insect host plant selection in complex environments

Abstract: Selection of suitable host plants is essential for the development and survival of herbivorous insects. Here we address behavioural mechanisms and the role of olfactory cues governing host choice, and their adaptive significance in complicated ecological contexts, with a focus on polyphagous insects. We also consider how recent developments in the study of olfactory systems of insects can provide a functional description of physiological mechanisms behind host plant choice. This may apply from the broader evolutionary history and local adaptations of olfactory receptor genes, to the underlying neural mechanisms behind innate host preferences and experience-based plasticity in host plant choice.

The molecular ticks of the Drosophila circadian clock.

Abstract: Drosophila is a powerful model to understand the mechanisms underlying circadian rhythms. The Drosophila molecular clock is comprised of transcriptional feedback loops. The expressions of the critical transcriptional activator CLK and its repressors PER and TIM are under tight transcriptional control. However, posttranslational modification of these proteins and regulation of their stability are critical to their function and to the generation of 24-hr period rhythms. We review here recent progress made in our understanding of PER, TIM and CLK posttranslational control. We also review recent studies that are uncovering the importance of novel regulatory mechanisms that affect mRNA stability and translation of circadian pacemaker proteins and their output.

Superorganism resilience: eusociality and susceptibility of ecosystem service providing insects to stressors.

Abstract: Insects provide crucial ecosystem services for human food security and maintenance of biodiversity. It is therefore not surprising that major declines in wild insects, combined with losses of managed bees, have raised great concern. Recent data suggest that honey bees appear to be less susceptible to stressors compared to other species. Here we argue that eusociality plays a key role for the susceptibility of insects to environmental stressors due to what we call superorganism resilience, which can be defined as the ability to tolerate the loss of somatic cells (=workers) as long as the germ line (=reproduction) is maintained. Life history and colony size appear critical for such resilience. Future conservation efforts should take superorganism resilience into account to safeguard ecosystem services by insects.

Causes of variation in wild bee responses to anthropogenic drivers.

Abstract: Anthropogenic change can have large impacts on wild bees and the pollination services they provide. However, the overall pattern of wild bee response to drivers such as land-use change, pesticides, pathogens, and climate change has been one of variability in both the magnitude and directionality of responses. We argue that two causes contribute to this variation. First, different species exhibit differential responses to the same anthropogenic drivers. Second, these anthropogenic drivers vary in type and magnitude that will drive variation in bee responses. For this second issue, we focus on land-use change, the most well-studied driver. We conclude by discussing how understanding species-level responses and the magnitude of land-use change can make bee conservation more effective.

Nutritional Control of Insect Reproduction.

Abstract: The amino acid-Target of Rapamycin (AA/TOR) and insulin pathways play a pivotal role in reproduction of female insects, serving as regulatory checkpoints that guarantee the sufficiency of nutrients for developing eggs. Being evolutionary older, the AA/TOR pathway functions as an initial nutritional sensor that not only activates nutritional responses in a tissue-specific manner, but is also involved in the control of insect insulin-like peptides (ILPs) secretion. Insulin and AA/TOR pathways also assert their nutritionally linked influence on reproductive events by contributing to the control of biosynthesis and secretion of juvenile hormone and ecdysone. This review covers the present status of our understanding of the contributions of AA/TOR and insulin pathways in insect reproduction.

The information landscape of plant constitutive and induced secondary metabolite production.

Abstract: Resistance against antagonist organisms, such as herbivores, has been identified as a major function of constitutive and stress-inducible production of plant secondary metabolites (PSMs). The mechanism through which constitutive expression and inducibility mediate resistance and, hence physiological and ecological factors that affect their evolution are still little understood. Here I propose information transfer as the least common denominator function of PSM production. In this framework constitutively produced PSMs represent the first line of defense through functioning as toxins, cues associated with toxicity and as detractants that interfere with antagonist host-search patterns. Information made available and utilizable by inducibility of secondary metabolite production allows plants to include the associated biological communities to cope with antagonists and to more efficiently target a specific attacker.

Death of the bee hive: understanding the failure of an insect society.

Abstract: Since 2007 honey bee colony failure rates overwinter have averaged about 30% across much of North America. In addition, cases of extremely rapid colony failure have been reported, which has been termed colony collapse disorder. Both phenomena result from an increase in the frequency and intensity of chronic diseases and environmental stressors. Colonies are often challenged by multiple stressors, which can interact: for example, pesticides can enhance disease transmission in colonies. Colonies may be particularly vulnerable to sublethal effects of pathogens and pesticides since colony functions are compromised whether a stressor kills workers, or causes them to fail at foraging. Modelling provides a way to understand the processes of colony failure by relating impacts of stressors to colony-level functions.

Integrated pest and pollinator management-adding a new dimension to an accepted paradigm.

Abstract: In this chapter we argue that while pesticides can be harmful to pollinators, when they are used in an integrated pest and pollinator management (IPPM) context, both pest management and pollinator protection may be achieved. Our growing knowledge of the impacts of pesticides on honey bees as well as bumble bees and solitary bees allows us to use the latitude we have in pest management including non-pesticidal pest management practices, changing pesticide types and incorporating other, less susceptible pollinator species into commercial practice. Pollinator health should be a central component of integrated pest management research, education and extension to produce viable IPPM approaches.

Applying high-throughput phenotyping to plant–insect interactions: picturing more resistant crops

Abstract: Through automated image collection and analysis, high-throughput phenotyping (HTP) systems non-destructively quantify a diversity of traits in large plant populations. Some platforms collect data in greenhouses or growth chambers while others are field-based. Platforms also vary in the number and type of sensors, including visible, fluorescence, infrared, hyperspectral, and three-dimensional cameras that can detect traits within and beyond the visible spectrum. These systems could be applied to quantify the impact of herbivores on plant health, to monitor herbivores in choice or no-choice bioassays, or to estimate plant properties such as defensive allelochemicals. By increasing the throughput, precision, and dimensionality of these measures, HTP has the potential to revolutionize the field of plant-insect interactions, including breeding programs for resistance and tolerance.

The comparative investigation of the stick insect and cockroach models in the study of insect locomotion

Abstract: Evolution has perfected very different six-legged walking machines from common neural and biomechanical components in an ancestral insect, as exemplified by the American cockroach and the stick insect Comparative experimental investigations of both intact animals and reduced neural preparations, integrated with mathematical modeling, have been instrumental in advancing our understanding of insect locomotion Locomotion in stick insects and cockroaches can be described by a related series of mathematical models that describe and quantify the effects of central coupling and feedback, and help explore the role of descending inputs (from higher neuronal centers) and neuromodulation Insights into sensory–motor interactions and adaptive motor control in insects are useful in designing more responsive, robust, and adaptable bio-robots, which, in turn, can contribute to hypothesis-testing in biology

Temperature, food quality and life history traits of herbivorous insects

Abstract: Population dynamics of herbivorous insects are strongly influenced by temperature and host plant quality; an interaction generally thought to be mediated via effects of temperature on metabolic rate and altered energy requirements. However, recent research suggests the relationship between nutrition, temperature, host plant quality and life history traits that influence insect fitness are more complex than appreciated to date. In the laboratory, rates of development are most strongly influenced by temperature, while growth, body composition, and reproductive output are greatly affected by nutrition, notably the uptake of protein and carbohydrate. However, individual outcomes and consequently population responses in the field are not readily predicted from data on ambient temperatures and host plant chemical composition. The relative amounts of protein and carbohydrate gained from a host plant depends on complex interactions between plant cell structure and leaf chemistry, combined with plasticity in feeding behaviour, microclimate selection, digestive and assimilative physiology. For example, grasshoppers can exploit the temperature dependence of host plant quality to maintain nutritional homeostasis. Consequently, understanding environmental interactions such as leaf defences and patterns of foraging, and predicting the effects of climate change on insect populations, will be complex.

Best Practices in Insect Genome Sequencing: What Works and What Doesn't

Abstract: The last decade of decreasing DNA sequencing costs and proliferating sequencing services in core labs and companies has brought the de-novo genome sequencing and assembly of insect species within reach for many entomologists. However, sequence production alone is not enough to generate a high quality reference genome, and in many cases, poor planning can lead to extremely fragmented genome assemblies preventing high quality gene annotation and other desired analyses. Insect genomes can be problematic to assemble, due to combinations of high polymorphism, inability to breed for genome homozygocity, and small physical sizes limiting the quantity of DNA able to be isolated from a single individual. Recent advances in sequencing technology and assembly strategies are enabling a revolution for insect genome reference sequencing and assembly. Here we review historical and new genome sequencing and assembly strategies, with a particular focus on their application to arthropod genomes. We highlight both the need to design sequencing strategies for the requirements of the assembly software, and new long-read technologies that are enabling a return to traditional assembly approaches. Finally, we compare and contrast very cost effective short read draft genome strategies with the long read approaches that although entailing additional cost, bring a higher likelihood of success and the possibility of archival assembly qualities approaching that of finished genomes.

Haplodiploidy and the reproductive ecology of Arthropods

Abstract: Approximately 15% of all arthropods reproduce through haplodiploidy. Yet it is unclear how this mode of reproduction affects other aspects of reproductive ecology. In this review we outline predictions on how haplodiploidy might affect mating system evolution, the evolution of traits under sexual or sexual antagonistic selection, sex allocation decisions and the evolution of parental care. We also give an overview of the phylogenetic distribution of haplodiploidy. Finally, we discuss how comparisons between different types of haplodiploidy (arrhenotoky, PGE with haploid vs somatically diploid males) might help to discriminate between the effects of virgin birth, haploid gene expression and those of haploid gene transmission.

Impacts of insect oral secretions on defoliation-induced plant defense

Abstract: Plant responses to biotic stress involve non-self perception, signaling, and altered defense phenotypes. During attack, defoliating insects deposit gland secretions (GS) and complex foregut derived oral secretions (OS) that include GS and combined products of plant, insect, and microbial interactions. GS-derived and OS-derived biochemicals that trigger defense are termed Herbivore Associated Molecular Patterns (HAMPs) while those that promote susceptibility are termed effectors. These functions are highly context and species specific. The magnitude and direction of plant responses are orchestrated by the interaction of damage, OS/GS components, predicted receptor-ligand interactions, ion fluxes, protein kinase signaling cascades, phytohormone interactions, transcription factor activation, altered translation, and defense biosynthesis. Unlike plant-pathogen recognition, a remaining challenge is the discovery of plant receptors for defoliator-derived HAMPs.

Insect effectors and gene-for-gene interactions with host plants

Abstract: Within the context of the four-phase model of plant immunity, gene-for-gene interactions have gained new relevance. Genes conferring resistance to the Asian rice gall midge (Orseolia oryzae) and the small brown planthopper (Nilaparvata lugens) have been cloned in rice (Oryza sativa). Mutations in insect avirulence genes that defeat plant resistance have been identified and cloned. Results are consistent with both the gene-for-gene hypothesis and the new model of plant immunity. Insect resistance genes encode proteins with nucleotide binding sites and leucine-rich repeats. Insects use effectors that elicit effector-triggered immunity. At least seven-percent of Hessian fly genes are effector encoding.

Circadian molecular clockworks in non-model insects.

Abstract: The recent development of molecular genetic technology is promoting studies on the clock mechanism of various non-model insect species, revealing diversity and commonality of their molecular clock machinery. Like in Drosophila, their clocks generally consist of clock genes including period, timeless, Clock, and cycle, except for hymenopteran species which lack timeless in their genome. Unlike in Drosophila, however, some insects show vertebrate-like traits: The clock machinery involves mammalian type cryptochrome, cycle is rhythmically expressed, and Clock is constitutively expressed. Although the oscillatory mechanisms of the clock are still to be investigated in most insects, RNAi and genome editing technology should accelerate the study, leading toward understanding the origin of variable overt behavioral rhythms such as nocturnal, diurnal, and crepuscular activity rhythms.

Nutrition-dependent control of insect development by insulin-like peptides.

Abstract: In metazoans, members of the insulin-like peptide (ILP) family play a role in multiple physiological functions in response to the nutritional status. ILPs have been identified and characterized in a wide variety of insect species. Insect ILPs that are mainly produced by several pairs of medial neurosecretory cells in the brain circulate in the hemolymph and act systemically on target tissues. Physiological and biochemical studies in Lepidoptera and genetic studies in the fruit fly have greatly expanded our knowledge of the physiological functions of ILPs. Here, we outline the recent progress of the structural classification of insect ILPs and overview recent studies that have elucidated the physiological functions of insect ILPs involved in nutrient-dependent growth during development.