Behavioral responses of the invasive fly Philornis downsi to stimuli from bacteria and yeast in the laboratory and the field in the Galapagos Islands
. Insects 2019
. Publisher's VersionAbstract
Philornis downsi Dodge and Aitken (Diptera: Muscidae) is an avian parasitic fly that has invaded the Galapagos archipelago and exerts an onerous burden on populations of endemic land birds. As part of an ongoing effort to develop tools for the integrated management of this fly, our objective was to determine its long-and short-range responses to bacterial and fungal cues associated with adult P. downsi. We hypothesized that the bacterial and fungal communities would elicit attraction at distance through volatiles, and appetitive responses upon contact. Accordingly, we amplified bacteria from guts of adult field-caught flies and from bird feces, and yeasts from fermenting papaya juice (a known attractant of P. downsi), on selective growth media, and assayed the response of flies to these microbes or their exudates. In the field, we baited traps with bacteria or yeast and monitored adult fly attraction. In the laboratory, we used the proboscis extension response (PER) to determine the sensitivity of males and females to tarsal contact with bacteria or yeast. Long range trapping efforts yielded two female flies over 112 trap-nights (attracted by bacteria from bird feces and from the gut of adult flies). In the laboratory, tarsal contact with stimuli from gut bacteria elicited significantly more responses than did yeast stimuli. We discuss the significance of these findings in context with other studies in the field and identify targets for future work. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
Natural Variation in Flower Color and Scent in Populations of Eruca sativa (Brassicaceae) Affects Pollination Behavior of Honey Bees
. Journal of Insect Science 2019
. Publisher's VersionAbstract
Plants of Eruca sativa Mill. (Brassicaceae) from desert and Mediterranean populations in Israel differ in flower color and size. In the desert habitat, the population has higher abundance of flowers with cream color and longer petals, whereas in the Mediterranean habitat, the population has higher abundance of flowers with yellow and shorter petals. Choice experiments with honey bee foragers (Apis mellifera Linn., Apidae, Hymenoptera), the main pollinator in the natural habitat in Israel, confirmed that they are more attracted to the yellow flower morph than to the cream one. A proboscis extension response test indicated that honey bees are able to discriminate between flower scents of the desert and Mediterranean populations. Considering the advantage of plants of the yellow morph in attracting pollinators, we further tested in a common garden experiment whether these possess higher fitness than plants of the desert population. Indeed, a significant association was found between flower color and fruit set, and seed mass. In general, our results provide evidence for ecotypic differentiation between populations imposed by pollinators. The advantage of the yellow color morph in attracting pollinators may explain its dominance among plants of the Mediterranean population. We discuss why the cream color morph may be dominant in the desert habitat, considering the possibility of different pollinators, tradeoffs between traits, or pleiotropy. © 2019 The Author(s).
Maleness-on-the-Y (MoY) orchestrates male sex determination in major agricultural fruit fly pests
. Science 2019
, 1457-1460. Publisher's VersionAbstract
In insects, rapidly evolving primary sex-determining signals are transduced by a conserved regulatory module controlling sexual differentiation. In the agricultural pest Ceratitis capitata (Mediterranean fruit fly, or Medfly), we identified a Y-linked gene, Maleness-on-the-Y (MoY), encoding a small protein that is necessary and sufficient for male development. Silencing or disruption of MoY in XY embryos causes feminization, whereas overexpression of MoY in XX embryos induces masculinization. Crosses between transformed XY females and XX males give rise to males and females, indicating that a Ychromosome can be transmitted by XY females. MoY is Y-linked and functionally conserved in other species of the Tephritidae family, highlighting its potential to serve as a tool for developing more effective control strategies against these major agricultural insect pests. Copyright © 2019 The Authors.
Complete assembly of the genome of an Acidovorax citrulli strain reveals a naturally occurring plasmid in this species
. Frontiers in Microbiology 2019
. Publisher's VersionAbstract
Acidovorax citrulli is the causal agent of bacterial fruit blotch (BFB), a serious threat to cucurbit crop production worldwide. Based on genetic and phenotypic properties, A. citrulli strains are divided into two major groups: group I strains have been generally isolated from melon and other non-watermelon cucurbits, while group II strains are closely associated with watermelon. In a previous study, we reported the genome of the group I model strain, M6. At that time, the M6 genome was sequenced by MiSeq Illumina technology, with reads assembled into 139 contigs. Here, we report the assembly of the M6 genome following sequencing with PacBio technology. This approach not only allowed full assembly of the M6 genome, but it also revealed the occurrence of a ∼53 kb plasmid. The M6 plasmid, named pACM6, was further confirmed by plasmid extraction, Southern-blot analysis of restricted fragments and obtention of M6-derivative cured strains. pACM6 occurs at low copy numbers (average of ∼4.1 ± 1.3 chromosome equivalents) in A. citrulli M6 and contains 63 open reading frames (ORFs), most of which (55.6%) encoding hypothetical proteins. The plasmid contains several genes encoding type IV secretion components, and typical plasmid-borne genes involved in plasmid maintenance, replication and transfer. The plasmid also carries an operon encoding homologs of a Fic-VbhA toxin-antitoxin (TA) module. Transcriptome data from A. citrulli M6 revealed that, under the tested conditions, the genes encoding the components of this TA system are among the highest expressed genes in pACM6. Whether this TA module plays a role in pACM6 maintenance is still to be determined. Leaf infiltration and seed transmission assays revealed that, under tested conditions, the loss of pACM6 did not affect the virulence of A. citrulli M6. We also show that pACM6 or similar plasmids are present in several group I strains, but absent in all tested group II strains of A. citrulli. Copyright © 2019 Yang, Santos Garcia, Pérez Montaño, da Silva, Zhao, Jiménez Guerrero, Rosenberg, Chen, Plaschkes, Morin, Walcott and Burdman.
Chitin/Chitosan: Versatile Ecological, Industrial, and Biomedical Applications
. In Extracellular Sugar-Based Biopolymers Matrices
; Extracellular Sugar-Based Biopolymers Matrices; Springer International Publishing: Cham, 2019; pp. 541–624. Publisher's VersionAbstract
Chitin is a linear polysaccharide of N-acetylglucosamine, which is highly abundant in nature and mainly produced by marine crustaceans. Chitosan is obtained by hydrolytic deacetylation. Both polysaccharides are renewable resources, simply and cost-effectively extracted from waste material of fish industry, mainly crab and shrimp shells. Research over the past five decades has revealed that chitosan, in particular, possesses unique and useful characteristics such as chemical versatility, polyelectrolyte properties, gel- and film-forming ability, high adsorption capacity, antimicrobial and antioxidative properties, low toxicity, and biocompatibility and biodegradability features. A plethora of chemical chitosan derivatives have been synthesized yielding improved materials with suggested or effective applications in water treatment, biosensor engineering, agriculture, food processing and storage, textile additives, cosmetics fabrication, and in veterinary and human medicine. The number of studies in this research field has exploded particularly during the last two decades. Here, we review recent advances in utilizing chitosan and chitosan derivatives in different technical, agricultural, and biomedical fields.
Individual and Colony Level Foraging Decisions of Bumble Bees and Honey Bees in Relation to Balancing of Nutrient Needs
. Frontiers in Ecology and Evolution 2019
177. Publisher's VersionAbstract
Foraging decisions of social animals occur in the context of social groups, and thus may be subject to considerations of not only an individual's nutritional state and nutrient input, but those of the social group in which they live. In eusocial insects, which live in colonies containing workers that forage for food that is mostly consumed by others, foraging decisions that reflect colony needs may also be considered at both the colony and individual level. If colony energy balance is perturbed, is the counteracting response occurring on the group level (a change in division of labor) or on the individual level (a change in individual foraging choices)? To address this, colony and individual level foraging behaviors were observed in two species of eusocial bees: the highly social honey bee Apis mellifera and the primitively eusocial bumble bee Bombus terrestris. After manipulations of protein (P) and carbohydrate (C) stores in colonies of both species, there were changes in multiple different behavioral responses including colony level (number of foragers, allocation to nectar and pollen foraging, nutrient mass foraged) and individual level (P and C concentration preference and loading during foraging). These results suggest both honey bee and bumble bee colonies balance nutrient needs through a combination of both colony level shifts in foraging allocation, as well as slight modulation of individual nutrient preferences. This study also uncovered colony level differences between the two bee species; honey bees balanced P intake while bumble bees balanced C intake. These patterns may reflect differences in life history traits such as perenniality and hoarding, traits that are developed in more highly social species. Overall, this study highlights the importance of considering both group and individual level behavioral responses in foraging decisions in social animals.
Intestinal bacteria modulate the foraging behavior of the oriental fruit fly Bactrocera dorsalis (Diptera: Tephritidae)
. PLoS One 2019
The gut microbiome of insects directly or indirectly affects the metabolism, immune status, sensory perception and feeding behavior of its host. Here, we examine the hypothesis that in the oriental fruit fly (Bactrocera dorsalis, Diptera: Tephritidae), the presence or absence of gut symbionts affects foraging behavior and nutrient ingestion. We offered protein-starved flies, symbiotic or aposymbiotic, a choice between diets containing all amino acids or only the non-essential ones. The different diets were presented in a foraging arena as drops that varied in their size and density, creating an imbalanced foraging environment. Suppressing the microbiome resulted in significant changes of the foraging behavior of both male and female flies. Aposymbiotic flies responded faster to the diets offered in experimental arenas, spent more time feeding, ingested more drops of food, and were constrained to feed on time-consuming patches (containing small drops of food), when these offered the full complement of amino acids. We discuss these results in the context of previous studies on the effect of the gut microbiome on host behavior, and suggest that these be extended to the life history dimension.
Symbiotic bacteria affect oviposition behavior in the olive fruit fly Bactrocera oleae
. J Insect Physiol 2019
Microbial associations are widespread across the insects. In the olive fruit fly Bactrocera oleae (Diptera: Tephritidae), vertically transmitted gut symbionts contribute to larval development inside the olive host, and to adult nutrition. Nevertheless, their effect on behavioural decisions of adults is unknown. In this study, we show that symbiotic bacteria affect oviposition behaviour in B. oleae. We studied the effect of different fruits as hosts and different gut-bacteria as gut-symbionts on oviposition attempts and fly development in B. oleae. Untreated flies that had native gut-symbionts attempted oviposition significantly more times than axenic flies as well as flies treated with medfly-associated Pantoea or Klebsiella bacteria. Axenic flies provided with a diet containing the homogenized gut of symbiotic flies recovered the same number of oviposition attempts as their symbiotic counterparts. As for as the different hosts, green olives (unripe) and grapes were preferred while black olives (ripe) elicited the least number of oviposition attempts, with an interactive effect of host and bacterial treatments. It appears that both the host attributes and the native gut-symbionts drive oviposition preference towards green olives in B. oleae. Moreover, both bacterial treatments and hosts significantly affected the development of B. oleae larvae. Though grapes elicited as many oviposition attempts as green olives, they yielded no pupae. Taken together, our results suggest that the intimate association between B. oleae and their gut-microbes, extends beyond nutritional support to behaviour.
A Transmissible RNA Pathway in Honey Bees
. Cell Rep 2019
Systemic RNAi, initiated by double-stranded RNA (dsRNA) ingestion, has been reported in diverse invertebrates, including honey bees, demonstrating environmental RNA uptake that undermines homologous gene expression. However, the question why any organism would take up RNA from the environment has remained largely unanswered. Here, we report on horizontal RNA flow among honey bees mediated by secretion and ingestion of worker and royal jelly diets. We demonstrate that transmission of jelly-secreted dsRNA to larvae is biologically active and triggers gene knockdown that lasts into adulthood. Worker and royal jellies harbor differential naturally occurring RNA populations. Jelly RNAs corresponded to honey bee protein-coding genes, transposable elements, and non-coding RNA, as well as bacteria, fungi, and viruses. These results reveal an inherent property of honey bees to share RNA among individuals and generations. Our findings suggest a transmissible RNA pathway, playing a role in social immunity and signaling between members of the hive.
The sulcatone receptor of the strict nectar-feeding mosquito Toxorhynchites amboinensis
. Insect Biochemistry and Molecular Biology 2019
, 103174. Publisher's VersionAbstract
Controlling Ae. aegypti populations and the prevention of mosquito bites includes the development of monitoring, repelling and attract-and-kill strategies that are based on understanding the chemical ecology of these pests. Olfactory-mediated attraction to mammals has recently been linked to the mosquito Aedes aegypti odorant receptor Or4, which is activated by animal-released 6-Methyl-5-hepten-2-one (sulcatone). This odorant is also a major component of flower scents and may play a role outside animal-host seeking. To explore the role of this chemical cue, we looked at the interaction between sulcatone and an Or4 homolog expressed in the antennae of the strict nectar-feeding mosquito Toxorhynchites amboinensis. Using the two-electrode voltage clamp of Xenopus oocytes as a heterologous expression system, we show that this receptor is a high intensity sulcatone receptor comparable to its Aedes counterparts. We also show that OR4 is activated by other aliphatic ketones and is inhibited by DEET. This pharmacological characterization suggests that sulcatone may be operating in more than one context in the Culicidae family.
Integral gene drives for population replacement
. Biol Open 2019
A first generation of CRISPR-based gene drives has now been tested in the laboratory in a number of organisms, including malaria vector mosquitoes. Challenges for their use in the area-wide genetic control of vector-borne disease have been identified, including the development of target site resistance, their long-term efficacy in the field, their molecular complexity, and practical and legal limitations for field testing of both gene drive and coupled anti-pathogen traits. We have evaluated theoretically the concept of integral gene drive (IGD) as an alternative paradigm for population replacement. IGDs incorporate a minimal set of molecular components, including drive and anti-pathogen effector elements directly embedded within endogenous genes - an arrangement that in theory allows targeting functionally conserved coding sequences without disrupting their function. Autonomous and non-autonomous IGD strains could be generated, optimized, regulated and imported independently. We performed quantitative modeling comparing IGDs with classical replacement drives and show that selection for the function of the hijacked host gene can significantly reduce the establishment of resistant alleles in the population, while drive occurring at multiple genomic loci prolongs the duration of transmission blockage in the face of pre-existing target site variation. IGD thus has potential as a more durable and flexible population replacement strategy.
Supersensitive Odorant Receptor Underscores Pleiotropic Roles of Indoles in Mosquito Ecology
. Frontiers in Cellular Neuroscience 2019
, 533. Publisher's VersionAbstract
Mosquitoes exhibit highly diverse and fast evolving odorant receptors. The indole-sensitive odorant receptor gene clade, comprised of Or2 and Or10 is a notable exception on account of its conservation in both mosquito subfamilies. This group of paralogous genes exhibits a complex developmental expression pattern in Aedes aegypti: AaegOr2 is expressed in both adults and larvae, AaegOr10 is adult-specific and a third member named AaegOr9 is larva-specific. OR2 and OR10 have been deorphanized and are selectively activated by indole and skatole, respectively. Using the two-electrode voltage clamp of Xenopus oocytes expressing Ae. aegypti ORs, we show that AaegOR9 is supersensitive and narrowly tuned to skatole. Our findings suggest that Ae. aegypti has evolved two distinct molecular strategies to detect skatole in aquatic and terrestrial environments, highlighting the central ecological roles of indolic compounds in the evolutionary and life histories of these insects.
The evolutionarily conserved indolergic receptors of the non-hematophagous elephant mosquito Toxorhynchites amboinensis
. Insect Biochemistry and Molecular Biology 2019
, 45 - 51. Publisher's VersionAbstract
The conservation of the mosquito indolergic receptors across the Culicinae and Anophelinae mosquito lineages, which spans 200 million years of evolution, is a testament to the central role of indolic compounds in the biology of these insects. Indole and skatole have been associated with the detection of oviposition sites and animal hosts. To evaluate the potential ecological role of these two compounds, we have used a pharmacological approach to characterize homologs of the indolergic receptors Or2 and Or10 in the non-hematophagous elephant mosquito Toxorhynchites amboinensis. We provide evidence that both receptors are narrowly tuned to indole and skatole like their counterparts from hematophagous mosquitoes. These findings indicate that Toxorhynchites detects indole and skatole in an ecological context to be determined and underscore the importance of understanding the role of these compounds in mosquitoes.
National scale mapping of ecosystem services in Israel - Genetic resources, pollination and cultural services
. One Ecosystem 2018
. Publisher's VersionAbstract
The Israel - National Ecosystem Assessment (I-NEA) project aims to present a comprehensive picture of the state and trends of Israel’s ecosystem services across all ecosystems, by integrating existing data and information collected from a wide range of sources. Although there is a lack of information about the spatial distribution of ecosystem services’ provisioning in Israel, their mapping constitutes an important part of the assessment. In this paper, we present a national-scale mapping of three ecosystem services, each of them implemented using different methods: 1) Genetic resources service, mapped using spatial observations of the Crop Wild Relatives species; 2) potential of pollination service, which is provided by wild bees, mapped using an expert-based habitat model related to land use and land cover; and 3) cultural service of recreation, mapped by analysing the distribution of geotagged digital photographs uploaded to social media resources. The derived maps visualise, for the first time in Israel, the spatially distributed values of the three ecosystem services. Supply hotspots with high values for all three services were identified, as well as spatial differences amongst the ecosystem services. These nationalscale maps provide overlooked insights and can be very useful for strategic discussions of stakeholders and decision-makers but should be regarded with caution given existing knowledge gaps and possible inaccuracies due to data scarcity and low resolution. © Lotan A et al.
Nutritional Physiology and Ecology of Honey Bees
. Annu Rev Entomol 2018
Honey bees feed on floral nectar and pollen that they store in their colonies as honey and bee bread. Social division of labor enables the collection of stores of food that are consumed by within-hive bees that convert stored pollen and honey into royal jelly. Royal jelly and other glandular secretions are the primary food of growing larvae and of the queen but are also fed to other colony members. Research clearly shows that bees regulate their intake, like other animals, around specific proportions of macronutrients. This form of regulation is done as individuals and at the colony level by foragers.
Redkmer: An Assembly-Free Pipeline for the Identification of Abundant and Specific X-Chromosome Target Sequences for X-Shredding by CRISPR Endonucleases
. The CRISPR journal 2018
88 - 98. Publisher's VersionAbstract
CRISPR-based synthetic sex ratio distorters, which operate by shredding the X-chromosome during male meiosis, are promising tools for the area-wide control of harmful insect pest or disease vector species. X-shredders have been proposed as tools to suppress insect populations by biasing the sex ratio of the wild population toward males, thus reducing its natural reproductive potential. However, to build synthetic X-shredders based on CRISPR, the selection of gRNA targets, in the form of high-copy sequence repeats on the X chromosome of a given species, is difficult, since such repeats are not accurately resolved in genome assemblies and cannot be assigned to chromosomes with confidence. We have therefore developed the redkmer computational pipeline, designed to identify short and highly abundant sequence elements occurring uniquely on the X chromosome. Redkmer was designed to use as input minimally processed whole genome sequence data from males and females. We tested redkmer with short- and long-read whole genome sequence data of Anopheles gambiae, the major vector of human malaria, in which the X-shredding paradigm was originally developed. Redkmer established long reads as chromosomal proxies with excellent correlation to the genome assembly and used them to rank X-candidate kmers for their level of X-specificity and abundance. Among these, a high-confidence set of 25-mers was identified, many belonging to previously known X-chromosome repeats of Anopheles gambiae, including the ribosomal gene array and the selfish elements harbored within it. Data from a control strain, in which these repeats are shared with the Y chromosome, confirmed the elimination of these kmers during filtering. Finally, we show that redkmer output can be linked directly to gRNA selection and off-target prediction. In addition, the output of redkmer, including the prediction of chromosomal origin of single-molecule long reads and chromosome specific kmers, could also be used for the characterization of other biologically relevant sex chromosome sequences, a task that is frequently hampered by the repetitiveness of sex chromosome sequence content.
Rationally-engineered reproductive barriers using CRISPR & CRISPRa: an evaluation of the synthetic species concept in Drosophila melanogaster
13125. Publisher's VersionAbstract
The ability to erect rationally-engineered reproductive barriers in animal or plant species promises to enable a number of biotechnological applications such as the creation of genetic firewalls, the containment of gene drives or novel population replacement and suppression strategies for genetic control. However, to date no experimental data exist that explores this concept in a multicellular organism. Here we examine the requirements for building artificial reproductive barriers in the metazoan model Drosophila melanogaster by combining CRISPR-based genome editing and transcriptional transactivation (CRISPRa) of the same loci. We directed 13 single guide RNAs (sgRNAs) to the promoters of 7 evolutionary conserved genes and used 11 drivers to conduct a misactivation screen. We identify dominant-lethal activators of the eve locus and find that they disrupt development by strongly activating eve outside its native spatio-temporal context. We employ the same set of sgRNAs to isolate, by genome editing, protective INDELs that render these loci resistant to transactivation without interfering with target gene function. When these sets of genetic components are combined we find that complete synthetic lethality, a prerequisite for most applications, is achievable using this approach. However, our results suggest a steep trade-off between the level and scope of dCas9 expression, the degree of genetic isolation achievable and the resulting impact on fly fitness. The genetic engineering strategy we present here allows the creation of single or multiple reproductive barriers and could be applied to other multicellular organisms such as disease vectors or transgenic organisms of economic importance.
A perspective on the need and current status of efficient sex separation methods for mosquito genetic control
. Parasit Vectors 2018
Major efforts are currently underway to develop novel, complementary methods to combat mosquito-borne diseases. Mosquito genetic control strategies (GCSs) have become an increasingly important area of research on account of their species-specificity, track record in targeting agricultural insect pests, and their environmentally non-polluting nature. A number of programs targeting Aedes and Anopheles mosquitoes, vectors of human arboviruses and malaria respectively, are currently being developed or deployed in many parts of the world. Operationally implementing these technologies on a large scale however, beyond proof-of-concept pilot programs, is hampered by the absence of adequate sex separation methods. Sex separation eliminates females in the laboratory from male mosquitoes prior to release. Despite the need for sex separation for the control of mosquitoes, there have been limited efforts in recent years in developing systems that are fit-for-purpose. In this special issue of Parasites and Vectors we report on the progress of the global Coordinated Research Program on "Exploring genetic, molecular, mechanical and behavioural methods for sex separation in mosquitoes" that is led by the Insect Pest Control Subprogramme of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture with the specific aim of building efficient sex separation systems for mosquito species. In an effort to overcome current barriers we briefly highlight what we believe are the three main reasons why progress has been so slow in developing appropriate sex separation systems: the availability of methods that are not scalable, the difficulty of building the ideal genetic systems and, finally, the lack of research efforts in this area.