Volatile allosteric antagonists of mosquito odorant receptors inhibit human-host attraction
. JOURNAL OF BIOLOGICAL CHEMISTRY 2021
Odorant-dependent behaviors in insects are triggered by the binding of odorant ligands to the variable subunits of heteromeric olfactory receptors. Previous studies have shown, however, that specific odor binding to ORco, the common subunit of odorant receptor heteromers, may allosterically alter olfactory receptor function and profoundly affect subsequent behavioral responses. Using an insect cell-based screening platform, we identified and characterized several antagonists of the odorant receptor coreceptor of the African malaria vector Anopheles gambiae (AgamORco) in a small collection of natural volatile organic compounds. Because some of the identified antagonists were previously shown to strongly repel Anopheles and Culex mosquitoes, we examined the bioactivities of the identified antagonists against Aedes, the third major genus of the Culicidae family. The tested antagonists inhibited the function of Ae. aegypti ORco ex vivo and repelled adult Asian tiger mosquitoes (Ae. albopictus). Binary mixtures of specific antagonists elicited higher repellency than single antagonists, and binding competition assays suggested that this enhanced repellence is due to antagonist interaction with distinct ORco sites. Our results also suggest that the enhanced mosquito repellency by antagonist mixtures is due to additive rather than synergistic effects of the specific antagonist combinations on ORco function. Taken together, these findings provide novel insights concerning the molecular aspects of odorant receptor function. Moreover, our results demonstrate that a simple screening assay may be used for the identification of allosteric modifiers of olfactory-driven behaviors capable of providing enhanced personal protection against multiple mosquito-borne infectious diseases.
Activation and detoxification of cassava cyanogenic glucosides by the whitefly Bemisia tabaci
. SCIENTIFIC REPORTS 2021
Two-component plant defenses such as cyanogenic glucosides are produced by many plant species, but phloem-feeding herbivores have long been thought not to activate these defenses due to their mode of feeding, which causes only minimal tissue damage. Here, however, we report that cyanogenic glycoside defenses from cassava (Manihot esculenta), a major staple crop in Africa, are activated during feeding by a pest insect, the whitefly Bemisia tabaci, and the resulting hydrogen cyanide is detoxified by conversion to beta-cyanoalanine. Additionally, B. tabaci was found to utilize two metabolic mechanisms to detoxify cyanogenic glucosides by conversion to non-activatable derivatives. First, the cyanogenic glycoside linamarin was glucosylated 1-4 times in succession in a reaction catalyzed by two B. tabaci glycoside hydrolase family 13 enzymes in vitro utilizing sucrose as a co-substrate. Second, both linamarin and the glucosylated linamarin derivatives were phosphorylated. Both phosphorylation and glucosidation of linamarin render this plant pro-toxin inert to the activating plant enzyme linamarase, and thus these metabolic transformations can be considered pre-emptive detoxification strategies to avoid cyanogenesis.
Decision support for pest management: Using field data for optimizing temperature-dependent population dynamics models
. ECOLOGICAL MODELLING 2021
Insect physiology is highly dependent on the environmental temperature, and the relationship can be mathematically defined. Thus, many models that aim to predict insect-pest population dynamics, use meteorological data as input to descriptive functions that predict the development rate, survival and reproduction of pest populations. In most cases, however, these functions/models are laboratory-driven and are based on data from constant-temperature experiments. Therefore, they lack an important optimization and validation steps that test their accuracy under field conditions. Here, we developed a realistic and robust regional framework for modeling the field population dynamics of the global insect pest Bemisia tabaci. First, two non-linear functions, development rate (DR) and female reproduction (EN) were fitted to data collected in constant temperature experiments. Next, nine one-generation field experiments were conducted in order to establish a field-derived database of insect performance, representing a variety of growing conditions (different seasons, regions and host plants). Then, sensitivity analyses were performed for identifying the optimal time-scale for which the running-averaged temperatures should be fed to the model. Setting the time to 6 h (i.e., each of the 24-time steps per day represents the last 6 h average) produced the best fit (RMSD score of 1.59 days, 5.7% of the mean) between the field observations and the model simulations. We hypothesize that the 6 h `relevant biological time-scale' captures the insect's physiological memory of daily cycling temperature events. Lastly, we evaluated the potential of the developed modeling framework to serve as a decision support tool in pest-management programs by correlating the model predictions with field-observations of three pest control inspectors during 2019. The model successfully predicted the first notable appearance of the insect in the field (completion of the third generation in May). Also, the model correctly identified the sharp rise in abundance (outbreak point) in mid-July (completion of the fifth generation), and the persistent rise in abundance through August and September. Comparing the simulations of the 2018 and 2019 seasons indicated that the model can also serve as a tool for retrospective systematic assessment of major decisions. Taken together, these data demonstrate the model robustness and its potential to provide an excellent decision-making support platform in regional control of pest species.
Domestication-related changes in sexual performance of Queensland fruit fly
. INSECT SCIENCE 2021
In Sterile Insect Technique (SIT) programs, massive numbers of insects are reared, sterilized, and released in the field to impede reproduction of pest populations. The domestication and rearing processes used to produce insects for SIT programs may have significant evolutionary impacts on life history and reproductive biology. We assessed the effects of domestication on sexual performance of laboratory reared Queensland fruit fly,Bactrocera tryoni, by comparing an old (49 generations) and a young colony (5 generations). We evaluated mating propensity, mating latency, copula duration, sperm transfer, and ability to induce sexual inhibition in mates. Overall, both males and females from the old colony had greater mating propensity than those from the young colony. Copula duration was longer when females were from the old colony. There was no evidence of sexual isolation between the colonies as males and females from the two colonies had similar propensity to mate with flies from either colony. Males from the old colony transferred more sperm regardless of which colony their mate was from. Finally, males from both colonies were similarly able to induce sexual inhibition in their mates and were also similarly able to secure copulations with already-mated females. Positive effects of domestication on sperm transfer, coupled with maintained ability to induce sexual inhibition in mates and to secure copulations with previously mated females, highlights that domestication may have little effect, or even positive effects, on some aspects of sexual performance that may advantage mass-rearedB. tryoniin SIT programs.
Profiling circulating microRNAs in the serum of pregnant and non-pregnant pigs reveals a plethora of reproductive status-dependent microRNAs
. ANIMAL 2021
Circulating, non-coding RNAs, such as microRNAs (miRNAs) have been proposed to be powerful pathophysiological indicators of pregnancy in animals and humans. Since their discovery, it is known that miRNAs can take part in numerous biological processes, including cell proliferation and differentiation during early embryonic development and establishment of pregnancy. Our recent studies have indicated that maternal blood can carry miRNAs reported previously at the embryo-maternal interface in pigs. To expand the scope of our research, we tested the hypothesis that miRNAs previously identified in conceptuses, trophoblasts, endometriumand uterine lumen-derived extracellular vesicles (EVs) collected before Day 20 of pregnancy can show reproductive status-dependent profiles in the serum of cyclic and pregnant crossbred pigs. Custom-designed TaqMan arrays, multiplex real-time reverse transcription (RT)-PCR and real-time RT-PCR allowed us to identify a number of reproductive status-dependent miRNAs in serum samples collected from pigs during the estrous cycle or pregnancy (Days 16 and 20). We found that serum samples were enriched with miRNAs involved in processes important during the estrous cycle and early pregnancy, e.g. cell sensitivity and viability, angiogenesis, embryonic cell proliferation and differentiation. Further validation revealed different abundance of ssc-miR-143-3p and sscmiR-125b in pregnant and non-pregnant animals and correlation of ssc-miR-125b levels with litter size. In addition, analyzed serum samples contained both EVs and Argonaute2 proteins, which are known to be involved in miRNA transportation and intercellular communication. In summary, we identified several circulating miRNAs that differ in abundance between cyclic and pregnant animals and could serve as potential indicators of reproductive status in pigs during breeding management. (C) 2021 The Authors. Published by Elsevier Inc. on behalf of The Animal Consortium.
Wild insect diversity increases inter-annual stability in global crop pollinator communities
. PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 2021
While an increasing number of studies indicate that the range, diversity and abundance of many wild pollinators has declined, the global area of pollinator-dependent crops has significantly increased over the last few decades. Crop pollination studies to date have mainly focused on either identifying different guilds pollinating various crops, or on factors driving spatial changes and turnover observed in these communities. The mechanisms driving temporal stability for ecosystem functioning and services, however, remain poorly understood. Our study quantifies temporal variability observed in crop pollinators in 21 different crops across multiple years at a global scale. Using data from 43 studies from six continents, we show that (i) higher pollinator diversity confers greater inter-annual stability in pollinator communities, (ii) temporal variation observed in pollinator abundance is primarily driven by the three-most dominant species, and (iii) crops in tropical regions demonstrate higher inter-annual variability in pollinator species richness than crops in temperate regions. We highlight the importance of recognizing wild pollinator diversity in agricultural landscapes to stabilize pollinator persistence across years to protect both biodiversity and crop pollination services. Short-term agricultural management practices aimed at dominant species for stabilizing pollination services need to be considered alongside longer term conservation goals focussed on maintaining and facilitating biodiversity to confer ecological stability.
Identification and functional characterization of olfactory indolergic receptors in Drosophila melanogaster
. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2021
Indole-sensitive odorant receptors or indolORs belong to a mosquito-specific expansion as ancient as the Culicidae lineage. Brachyceran flies appeared to lack representative members of this group despite the importance of indolics in this important group of dipterans. To explore whether indolORs occur in other brachyceran species, we searched for candidate indolORs in Drosophila melanogaster. Using phylogenetic tools, we show that D. melanogaster OR30a, OR43a, and OR49b form a distinct monophyletic lineage with mosquito indolORs. To explore a potential functional orthology with indolORs, we expressed these three Drosophila ORs in Xenopus laevis oocytes and measured their responses to a panel of indolic compounds. We provide evidence that OR30a, OR43a, and OR49b exhibit high sensitivity to indoles. Along with the recent discovery of indolORs in the housefly Musca domestica, our findings suggest that indolORs are a widespread feature of the peripheral olfactory systems of Diptera.
Metatranscriptome Analysis of Sympatric Bee Species Identifies Bee Virus Variants and a New Virus, Andrena-Associated Bee Virus-1
. VIRUSES-BASEL 2021
Bees are important plant pollinators in agricultural and natural ecosystems. High average annual losses of honey bee (Apis mellifera) colonies in some parts of the world, and regional population declines of some mining bee species (Andrena spp.), are attributed to multiple factors including habitat loss, lack of quality forage, insecticide exposure, and pathogens, including viruses. While research has primarily focused on viruses in honey bees, many of these viruses have a broad host range. It is therefore important to apply a community level approach in studying the epidemiology of bee viruses. We utilized high-throughput sequencing to evaluate viral diversity and viral sharing in sympatric, co-foraging bees in the context of habitat type. Variants of four common viruses (i.e., black queen cell virus, deformed wing virus, Lake Sinai virus 2, and Lake Sinai virus NE) were identified in honey bee and mining bee samples, and the high degree of nucleotide identity in the virus consensus sequences obtained from both taxa indicates virus sharing. We discovered a unique bipartite + ssRNA Tombo-like virus, Andrena-associated bee virus-1 (AnBV-1). AnBV-1 infects mining bees, honey bees, and primary honey bee pupal cells maintained in culture. AnBV-1 prevalence and abundance was greater in mining bees than in honey bees. Statistical modeling that examined the roles of ecological factors, including floral diversity and abundance, indicated that AnBV-1 infection prevalence in honey bees was greater in habitats with low floral diversity and abundance, and that interspecific virus transmission is strongly modulated by the floral community in the habitat. These results suggest that land management strategies that aim to enhance floral diversity and abundance may reduce AnBV-1 spread between co-foraging bees.
The molecular mechanisms that determine different degrees of polyphagy in the Bemisia tabaci species complex
. EVOLUTIONARY APPLICATIONS 2021
The whitefly Bemisia tabaci is a closely related group of >35 cryptic species that feed on the phloem sap of a broad range of host plants. Species in the complex differ in their host-range breadth, but the mechanisms involved remain poorly understood. We investigated, therefore, how six different B. tabaci species cope with the environmental unpredictability presented by a set of four common and novel host plants. Behavioral studies indicated large differences in performances on the four hosts and putative specialization of one of the species to cassava plants. Transcriptomic analyses revealed two main insights. First, a large set of genes involved in metabolism (>85%) showed differences in expression between the six species, and each species could be characterized by its own unique expression pattern of metabolic genes. However, within species, these genes were constitutively expressed, with a low level of environmental responsiveness (i.e., to host change). Second, within each species, sets of genes mainly associated with the super-pathways ``environmental information processing'' and ``organismal systems'' responded to the host switching events. These included genes encoding for proteins involved in sugar homeostasis, signal transduction, membrane transport, and immune, endocrine, sensory and digestive responses. Our findings suggested that the six B. tabaci species can be divided into four performance/transcriptomic ``Types'' and that polyphagy can be achieved in multiple ways. However, polyphagy level is determined by the specific identity of the metabolic genes/pathways that are enriched and overexpressed in each species (the species' individual metabolic ``tool kit'').
Engineered sex ratio distortion by X-shredding in the global agricultural pest Ceratitis capitata
. BMC BIOLOGY 2021
BackgroundGenetic sex ratio distorters are systems aimed at effecting a bias in the reproductive sex ratio of a population and could be applied for the area-wide control of sexually reproducing insects that vector disease or disrupt agricultural production. One example of such a system leading to male bias is X-shredding, an approach that interferes with the transmission of the X-chromosome by inducing multiple DNA double-strand breaks during male meiosis. Endonucleases targeting the X-chromosome and whose activity is restricted to male gametogenesis have recently been pioneered as a means to engineer such traits.ResultsHere, we enabled endogenous CRISPR/Cas9 and CRISPR/Cas12a activity during spermatogenesis of the Mediterranean fruit fly Ceratitis capitata, a worldwide agricultural pest of extensive economic significance. In the absence of a chromosome-level assembly, we analysed long- and short-read genome sequencing data from males and females to identify two clusters of abundant and X-chromosome-specific sequence repeats. When targeted by gRNAs in conjunction with Cas9, cleavage of these repeats yielded a significant and consistent distortion of the sex ratio towards males in independent transgenic strains, while the combination of distinct distorters induced a strong bias (similar to 80%).ConclusionWe provide a first demonstration of CRISPR-based sex distortion towards male bias in a non-model organism, the global pest insect Ceratitis capitata. Although the sex ratio bias reached in our study would require improvement, possibly through the generation and combination of additional transgenic lines, to result in a system with realistic applicability in the field, our results suggest that strains with characteristics suitable for field application can now be developed for a range of medically or agriculturally relevant insect species.
Sex-Dependent Effects of the Microbiome on Foraging and Locomotion in Drosophila suzukii
. FRONTIERS IN MICROBIOLOGY 2021
There is growing evidence that symbiotic microbes can influence multiple nutrition-related behaviors of their hosts, including locomotion, feeding, and foraging. However, how the microbiome affects nutrition-related behavior is largely unknown. Here, we demonstrate clear sexual dimorphism in how the microbiome affects foraging behavior of a frugivorous fruit fly, Drosophila suzukii. Female flies deprived of their microbiome (axenic) were consistently less active in foraging on fruits than their conventional counterparts, even though they were more susceptible to starvation and starvation-induced locomotion was notably more elevated in axenic than conventional females. Such behavioral change was not observed in male flies. The lag of axenic female flies but not male flies to forage on fruits is associated with lower oviposition by axenic flies, and mirrored by reduced food seeking observed in virgin females when compared to mated, gravid females. In contrast to foraging intensity being highly dependent on the microbiome, conventional and axenic flies of both sexes showed relatively consistent and similar fruit preferences in foraging and oviposition, with raspberries being preferred among the fruits tested. Collectively, this work highlights a clear sex-specific effect of the microbiome on foraging and locomotion behaviors in flies, an important first step toward identifying specific mechanisms that may drive the modulation of insect behavior by interactions between the host, the microbiome, and food.
Shifting microbiomes complement life stage transitions and diet of the bird parasite Philornis downsi from the Galapagos Islands
. ENVIRONMENTAL MICROBIOLOGY 2021
Domestication disconnects an animal from its natural environment and diet, imposing changes in the attendant microbial community. We examine these changes in Philornis downsi (Muscidae), an invasive parasitic fly of land birds in the Galapagos Islands. Using a 16S rDNA profiling approach we studied the microbiome of larvae and adults of wild and laboratory-reared populations. These populations diverged in their microbiomes, significantly more so in larval than in adult flies. In field-collected second-instar larvae, Klebsiella (70.3%) was the most abundant taxon, while in the laboratory Ignatzschineria and Providencia made up 89.2% of the community. In adults, Gilliamella and Dysgonomonas were key members of the core microbiome of field-derived females and males but had no or very low representation in the laboratory. Adult flies harbour sex-specific microbial consortia in their gut, as male core microbiomes were significantly dominated by Klebsiella. Thus, P. downsi microbiomes are dynamic and shift correspondingly with life cycle and diet. Sex-specific foraging behaviour of adult flies and nest conditions, which are absent in the laboratory, may contribute to shaping distinct larval, and adult male and female microbiomes. We discuss these findings in the context of microbe-host co-evolution and the implications for control measures.
Spatial patterning of scent in petunia corolla is discriminated by bees and involves the ABCG1 transporter
. PLANT JOURNAL 2021
Floral guides are patterned cues that direct the pollinator to the plant reproductive organs. The spatial distribution of showy visual and olfactory traits allows efficient plant-pollinator interactions. Data on the mechanisms underlying floral volatile patterns or their interactions with pollinators are lacking. Here we characterize the spatial emission patterns of volatiles from the corolla of the model plant Petunia x hybrida and reveal the ability of honeybees to distinguish these patterns. Along the adaxial epidermis, in correlation with cell density, the petal base adjacent to reproductive organs emitted significantly higher levels of volatiles than the distal petal rim. Volatile emission could also be differentiated between the two epidermal surfaces: emission from the adaxial side was significantly higher than that from the abaxial side. Similar emission patterns were also observed in other petunias, Dianthus caryophyllus (carnation) and Argyranthemum frutescens (Marguerite daisy). Analyses of transcripts involved in volatile production/emission revealed lower levels of the plasma-membrane transporter ABCG1 in the abaxial versus adaxial epidermis. Transient overexpression of ABCG1 enhanced emission from the abaxial epidermis to the level of the adaxial epidermis, suggesting its involvement in spatial emission patterns in the epidermal layers. Proboscis extension response experiments showed that differences in emission levels along the adaxial epidermis, that is, petal base versus rim, detected by GC-MS are also discernible by honeybees.