Resistant Flies Research Articles

Thermal developmental plasticity affects body size and water conservation of Drosophila nepalensis from the Western Himalayas.

In the Western Himalayas, Drosophila nepalensis is more abundant during the colder and drier winter than the warmer rainy season but the mechanistic bases of such adaptations are largely unknown. We tested effects of developmental plasticity on desiccation-related traits (body size, body melanization and water balance traits) that may be consistent with changes in seasonal abundance of this species. D. nepalensis grown at 15°C has shown twofold higher body size, greater melanization (∼15-fold), higher desiccation resistance (∼55h), hemolymph as well as carbohydrate content (twofold higher) as compared with corresponding values at 25°C. Water loss before succumbing to death was much higher (∼16%) at 15°C than 25°C. Developmental plastic effects on body size are associated with changes in water balance-related traits (bulk water, hemolymph and dehydration tolerance). The role of body melanization was evident from the analysis of assorted darker and lighter flies (from a mass culture of D. nepalensis reared at 21°C) which lacked differences in dry mass but showed differences in desiccation survival hours and rate of water loss. For adult acclimation, we found a slight increase in desiccation resistance of flies reared at lower growth temperature, whereas in flies reared at 25°C such a response was lacking. In D. nepalensis, greater developmental plasticity is consistent with its contrasting levels of seasonal abundance. Finally, in the context of global climate change in the Western Himalayas, D. nepalensis seems vulnerable in the warmer season due to lower adult as well as developmental acclimation potential at higher growth temperature (25°C).

Pelo is required for high efficiency viral replication.

Viruses hijack host factors for their high speed protein synthesis, but information about these factors is largely unknown. In searching for genes that are involved in viral replication, we carried out a forward genetic screen for Drosophila mutants that are more resistant or sensitive to Drosophila C virus (DCV) infection-caused death, and found a virus-resistant line in which the expression of pelo gene was deficient. Our mechanistic studies excluded the viral resistance of pelo deficient flies resulting from the known Drosophila anti-viral pathways, and revealed that pelo deficiency limits the high level synthesis of the DCV capsid proteins but has no or very little effect on the expression of some other viral proteins, bulk cellular proteins, and transfected exogenous genes. The restriction of replication of other types of viruses in pelo deficient flies was also observed, suggesting pelo is required for high level production of capsids of all kinds of viruses. We show that both pelo deficiency and high level DCV protein synthesis increase aberrant 80S ribosomes, and propose that the preferential requirement of pelo for high level synthesis of viral capsids is at least partly due to the role of pelo in dissociation of stalled 80S ribosomes and clearance of aberrant viral RNA and proteins. Our data demonstrated that pelo is a host factor that is required for high efficiency translation of viral capsids and targeting pelo could be a strategy for general inhibition of viral infection.

Resistance of the house fly Musca domestica (Diptera: Muscidae) to lambda-cyhalothrin: mode of inheritance, realized heritability, and cross-resistance to other insecticides

Lambda-cyhalothrin, a pyrethroid insecticide, has been used frequently for the control of house flies, Musca domestica L., worldwide including Pakistan. To assess the resistance risk and design a resistance management strategy, a house fly population was exposed to lambda-cyhalothrin in the laboratory to assess inheritance and heritability, and cross-resistance to other insecticides, including different chemical classes. After 11 generations of selection, the population developed 113.57-fold resistance to lambda-cyhalothrin compared to the susceptible population. There was no cross-resistance to bifenthrin and methomyl, but very low cross-resistance to abamectin and indoxacarb in the lambda-cyhalothrin selected population compared to the field population. Synergism bioassay with piperonyl butoxide and S,S,S-tributylphosphorotrithioate indicated that lambda-cyhalothrin resistance was associated with microsomal oxidases and esterases. The LC50 values of F1 (Lambda-SEL ♀ × Susceptible ♂) and F'1 (Lambda-SEL ♂ × Susceptible ♀) populations were not significantly different and dominance (DLC) values were 0.68 and 0.62. The resistance to lambda-cyhalothrin was completely recessive (DML = 0.00) at highest dose and completely dominant at lowest dose (DML = 0.95). The monogenic model of inheritance showed that lambda-cyhalothrin resistance was controlled by multiple factors. The heritability values were 0.20, 0.04, 0.003, 0.07 and 0.08 for lambda-cyhalothrin, bifenthrin, methomyl, indoxacarb and abamectin resistance, respectively. It was concluded that lambda-cyhalothrin resistance in house flies was autosomally inherited, incompletely dominant and controlled by multiple factors. These findings would be helpful to improve the management of house flies.

Genetics and mechanisms of imidacloprid resistance in house flies

Imidacloprid is the most widely used neonicotinoid insecticide against house flies, which are major pests at animal production facilities worldwide. However, cases of both physiological and behavior resistance have been reported. Recently, physiological resistance to imidacloprid was found in the United States (California and Florida). However, no studies have been undertaken to characterize this resistance in house flies from the United States.Three imidacloprid selections of a strain originally collected from Florida increased the level of resistance, ultimately resulting in a strain that had 2300-fold resistance in females and 130-fold in males. Imidacloprid resistance was not overcome with piperonyl butoxide (PBO) suggesting that resistance is not due to detoxification by cytochrome P450s. Resistance was mapped to autosomes 3 and 4. There was⩾100-fold cross-resistance to acetamiprid and dinotefuran, but no cross-resistance to spinosad. The resistance in this imidacloprid selected population was unstable and declined over a period of several months. The significance of these results to management of imidacloprid resistance in the field, and potential mechanisms of resistance involved, are discussed.

Methods for studying the biological consequences of endo-siRNA deficiency in Drosophila melanogaster.

Endogenous small interfering RNAs (endo-siRNAs) are a newly emerged class of small regulatory RNAs. In Drosophila melanogaster, the production of endo-siRNAs depends on the RNase III enzyme Dicer-2 (Dcr-2). Loss of dcr-2 function reduces the resistance of adult flies to various stresses and shortens their life span. The mutants also exhibit alterations in carbohydrate and lipid metabolism. These findings suggest that the endo-siRNA pathway plays a protective role during exposure to stress and aging in D. melanogaster, possibly by regulating metabolic homeostasis. Here, we describe the methods that were used to discover the phenotypes associated with endo-siRNA deficiency by using dcr-2 null mutants.

Altered regulation of sleep and feeding contributes to starvation resistance in Drosophila melanogaster.

Animals respond to changes in food availability by adjusting sleep and foraging strategies to optimize their fitness. Wild populations of the fruit fly, Drosophila melanogaster, display highly variable levels of starvation resistance that are dependent on geographic location, food availability and evolutionary history. How behaviors that include sleep and feeding vary in Drosophila with increased starvation resistance is unclear. We have generated starvation-resistant flies through experimental evolution to investigate the relationship between foraging behaviors and starvation resistance. Outbred populations of D. melanogaster were selected for starvation resistance over 60 generations. This selection process resulted in flies with a threefold increase in total lipids that survive up to 18 days without food. We tested starvation-selected (S) flies for sleep and feeding behaviors to determine the effect that selection for starvation resistance has had on foraging behavior. Flies from three replicated starvation-selected populations displayed a dramatic reduction in feeding and prolonged sleep duration compared to fed control (F) populations, suggesting that modified sleep and feeding may contribute to starvation resistance. A prolonged larval developmental period contributes to the elevated energy stores present in starvation-selected flies. By preventing S larvae from feeding longer than F larvae, we were able to reduce energy stores in adult S flies to the levels seen in adult F flies, thus allowing us to control for energy storage levels. However, the reduction of energy stores in S flies fails to generate normal sleep and feeding behavior seen in F flies with similar energy stores. These findings suggest that the behavioral changes observed in S flies are due to genetic regulation of behavior rather than elevated lipid levels. Testing S-F hybrid individuals for both feeding and sleep revealed a lack of correlation between food consumption and sleep duration, indicating further independence in genetic factors underlying the sleep and feeding changes observed in S flies. Taken together, these findings provide evidence that starvation selection results in prolonged sleep and reduced feeding through a mechanism that is independent of elevated energy stores. These findings suggest that changes in both metabolic function and behavior contribute to the increase in starvation resistance seen in flies selected for starvation resistance.

A whole transcriptomal linkage analysis of gene co-regulation in insecticide resistant house flies, Musca domestica

BackgroundStudies suggest that not only is insecticide resistance conferred via multiple gene up-regulation, but it is mediated through the interaction of regulatory factors. However, no regulatory factors in insecticide resistance have yet been identified, and there has been no examination of the regulatory interaction of resistance genes. Our current study generated the first reference transcriptome from the adult house fly and conducted a whole transcriptome analysis for the multiple insecticide resistant strain ALHF (wild-type) and two insecticide susceptible strains: aabys (with morphological recessive markers) and CS (wild type) to gain valuable insights into the gene interaction and complex regulation in insecticide resistance of house flies, Musca domestica.ResultsOver 56 million reads were used to assemble the adult female M. domestica transcriptome reference and 14488 contigs were generated from the de novo transcriptome assembly. A total of 6159 (43%) of the contigs contained coding regions, among which 1316 genes were identified as being co-up-regulated in ALHF in comparison to both aabys and CS. The majority of these up-regulated genes fell within the SCOP categories of metabolism, general, intra-cellular processes, and regulation, and covered three key detailed function categories: redox detailed function category in metabolism, signal transduction and kinases/phosphatases in regulation, and proteases in intra-cellular processes. The redox group contained detoxification gene superfamilies, including cytochrome P450s, glutathione S-transferases, and esterases. The signal transduction and kinases/phosphatases groups contained gene families of rhodopsin-like GPCRs, adenylate and guanylate cyclases, protein kinases and phosphatases. The proteases group contained genes with digestive, catalytic, and proteinase activities. Genetic linkage analysis with house fly lines comparing different autosomal combinations from ALHF revealed that the up-regulation of gene expression in the three key SCOP detailed function categories occurred mainly through the co-regulation of factors among multiple autosomes, especially between autosomes 2 and 5, suggesting that signaling transduction cascades controlled by GPCRs, protein kinase/phosphates and proteases may be involved in the regulation of resistance P450 gene regulation.ConclusionTaken together, our findings suggested that not only is insecticide resistance conferred via multi-resistance mechanisms or up-regulated genes, but it is mediated through the trans and/or cis co-regulations of resistance genes.

Insecticide resistance in house flies from the United States: Resistance levels and frequency of pyrethroid resistance alleles

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65–91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9–76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed.

Desiccation resistance of wild and mass-rearedBactrocera tryoni(Diptera: Tephritidae)

In pest management programmes that incorporate the sterile insect technique (SIT), the ability of mass-reared insects to tolerate dry conditions may influence their survival after release in the field. In the present study, desiccation resistance of adult mass-reared Queensland fruit flies, Bactrocera tryoni (Frogatt) (Diptera: Tephritidae), that are routinely released in SIT programmes was compared with that of wild flies at 1, 10 and 20 days after adult eclosion. Under dry conditions without access to food or water, longevity of mass-reared B. tryoni was significantly less than that of their wild counterparts. Desiccation resistance of mass-reared flies declined monotonically with age, but this was not the case for wild flies. The sharp decline in desiccation resistance of mass-reared flies as they aged was likely explained by decreased dehydration tolerance. As in an earlier study, desiccation resistance of females was significantly lower than that of males but this was particularly pronounced in mass-reared females. Female susceptibility to dry conditions corresponded with declining dehydration tolerance with age and associated patterns of reproductive development, which suggests that water content of their oocyte load is not available for survival during periods of water stress.

Declining signal dependence of Nrf2‐MafS‐regulated gene expression correlates with aging phenotypes

Aging is a degenerative process characterized by declining molecular, cell and organ functions, and accompanied by the progressive accumulation of oxidatively damaged macromolecules. This increased oxidative damage may be causally related to an age-associated dysfunction of defense mechanisms, which effectively protect young individuals from oxidative insults. Consistently, older organisms are more sensitive to acute oxidative stress exposures than young ones. In studies on the Drosophila Nrf2 transcription factor CncC, we have investigated possible causes for this loss of stress resistance and its connection to the aging process. Nrf2 is a master regulator of antioxidant and stress defense gene expression with established functions in the control of longevity. Here, we show that the expression of protective Nrf2/CncC target genes in unstressed conditions does not generally decrease in older flies. However, aging flies progressively lose the ability to activate Nrf2 targets in response to acute stress exposure. We propose that the resulting inability to dynamically adjust the expression of Nrf2 target genes to the organism's internal and external conditions contributes to age-related loss of homeostasis and fitness. In support of this hypothesis, we find the Drosophila small Maf protein, MafS, an Nrf2 dimerization partner, to be critical to maintain responsiveness of the Nrf2 system: overexpression of MafS in older flies preserves Nrf2/CncC signaling competence and antagonizes age-associated functional decline. The maintenance of acute stress resistance, motor function, and heart performance in aging flies overexpressing MafS supports a critical role for signal responsiveness of Nrf2 function in promoting youthful phenotypes.

Abamectin resistance in Drosophila is related to increased expression of P-glycoprotein via the dEGFR and dAkt pathways

Many insects have evolved resistance to abamectin but the mechanisms involved in this resistance have not been well characterized. P-glycoprotein (P-gp), an ATP-dependent drug-efflux pump transmembrane protein, may be involved in abamectin resistance. We investigated the role of P-gp in abamectin (ABM) resistance in Drosophila using an ABM-resistant strain developed in the laboratory. A toxicity assay, Western blotting analysis and a vanadate-sensitive ATPase activity assay all demonstrated the existence of a direct relationship between P-gp expression and ABM resistance in these flies. Our observations indicate that P-gp levels in flies' heads were higher than in their thorax and abdomen, and that both P-gp levels and LC50 values were higher in resistant than in susceptible and P-gp-deficient strains. In addition, P-gp levels in the blood–brain barrier (BBB) of resistant flies were higher than in susceptible and P-gp-deficient flies, which is further evidence that a high level of P-gp in the BBB is related to ABM resistance. Furthermore, we found greater expression of Drosophila EGFR (dEGFR) in the resistant strain than in the susceptible strain, and that the level of Drosophila Akt (dAkt) was much higher in resistant than in susceptible flies, whereas that in P-gp-deficient flies was very low. Compared to susceptible flies, P-gp levels in the resistant strain were markedly suppressed by the dEGFR and dAkt inhibitors lapatinib and wortmannin. These results suggest that the increased P-gp in resistant flies was regulated by the dEGFR and dAkt pathways and that increased expression of P-gp is an important component of ABM resistance in insects.

Resistance to conventional insecticides in Pakistani populations of Musca domestica L. (Diptera: Muscidae): a potential ectoparasite of dairy animals

The house fly, Musca domestica L., is an important hygienic pest of humans and dairy animals with the potential to develop resistance to most chemical classes of insecticides. Six adult house fly strains from dairy farms in Punjab, Pakistan were evaluated for resistance to selected insecticides from organochlorine, organophosphate, carbamate and pyrethroid classes. For a chlorocyclodiene and two organophosphates tested, the resistance ratios (RR) at LC50 were in the range of 5.60-22.02 fold for endosulfan, 7.66-23.24 fold for profenofos and 2.47-7.44 fold for chlorpyrifos. For two pyrethroids and one carbamate, the RR values at LC50 were 30.22-70.02 for cypermethrin, 5.73-18.31 for deltamethrin, and 4.39-15.50 for methomyl. This is the first report of resistance to different classes of insecticides in Pakistani dairy populations of house flies. Regular insecticide resistance monitoring programs on dairy farms are needed to prevent field control failures. Moreover, integrated approaches including the judicious use of insecticides are needed to delay the development of insecticide resistance in house flies.

Modulation of methuselah expression targeted to Drosophila insulin‐producing cells extends life and enhances oxidative stress resistance

Ubiquitously reduced signaling via Methuselah (MTH), a G-protein-coupled receptor (GPCR) required for neurosecretion, has previously been reported to extend life and enhance stress resistance in flies. Whether these effects are due to reduced MTH signalling in specific tissues remains unknown. We determined that reduced expression of mth targeted to the insulin-producing cells (IPCs) of the fly brain was sufficient to extend life and enhance oxidative stress resistance. Paradoxically, we discovered that overexpression of mth targeted to the same cells has similar phenotypic effects to reduced expression due to MTH's interaction with β-arrestin, which uncouples GPCRs from their G-proteins. We confirmed the functional relationship between MTH and β-arrestin by finding that IPC-targeted overexpression of β-arrestin alone mimics the longevity phenotype of reduced MTH signaling. As reduced MTH signaling also inhibits insulin secretion from the IPCs, the most parsimonious mechanistic explanation of its longevity and stress-resistance enhancement might be through reduced insulin/IGF signaling (IIS). However, examination of phenotypic features of long-lived IPC-mth modulated flies as well as several downstream IIS targets implicates enhanced activity of the JNK stress-resistance pathway more directly than insulin signaling in the longevity and stress-resistance phenotypes.

Multiple cytochrome P450s overexpressed in pyrethroid resistant house flies (Musca domestica)

Cytochrome P450 monooxygenases-mediated detoxification is a major mechanism of pyrethroid resistance in house flies. Constitutive overexpression of P450 genes is the main cause for this type of insecticide resistance. In this study, three new P450 genes (CYP6A40, CYP6D8 and CYP6G4) over-expressed in a pyrethroid resistance strain (BJD) were identified. Developmental expression analysis showed that CYP6A40 and CYP6D8 were expressed in all life stages, while CYP6G4 was not transcribed in eggs or larvae. Permethrin resistance and expression level of cytochrome P450s in six house fly populations (the BJD strain and five field-derived house fly populations collected across China) were determined. Compared with the susceptible TJS strain, all the six populations exhibited different levels of resistance to permethrin. Piperonyl butoxide (PBO) reduced permethrin resistance level up to 109-fold, indicating that cytochrome P450-mediated detoxification is responsible for pyrethroid resistance in Chinese house flies. Significant overexpression of more than one of the eight P450 genes (CYP6A5v1, CYP6A5v2, CYP6A36, CYP6A40, CYP6D1, CYP6D3, CYP6D8 and CYP6G4) in the six pyrethroid resistant house fly populations was observed. Differential expression patterns of P450s over-represented in the resistance populations suggested evolutionary plasticity of P450-mediated pyrethroid resistance. CYP6G4 and CYP6D1, commonly over-expressed in resistant populations, were hypothesized to be the important P450s contributing to pyrethroid resistance of Chinese house flies.

Truncated transcripts of nicotinic acetylcholine subunit gene Bdα6 are associated with spinosad resistance in Bactrocera dorsalis

Spinosad-resistance mechanisms of Bactrocera dorsalis, one of the most important agricultural pests worldwide, were investigated. Resistance levels to spinosad in a B. dorsalis strain from Taiwan were more than 2000-fold, but showed no cross resistance to imidacloprid or fipronil. Combined biochemical and synergistic data indicated that target-site insensitivity is the major resistance component. The gene encoding the nAChR subunit alpha 6 (Bdα6), the putative molecular target of spinosad, was isolated using PCR and RACE techniques. The full-length cDNA of Bdα6 from spinosad-susceptible strains had an open reading frame of 1467 bp and codes for a typical nAChR subunit. Two isoforms of exon 3 (3a and 3b) and exon 8 (8a and 8b), and four full-length splicing variants were found in the susceptible strain. All transcripts from the spinosad-resistant strain were truncated and coded for apparently non-functional Bdα6. Genetic linkage analysis further associated spinosad-resistance phenotype with the truncated Bdα6 forms. This finding is consistent with a previous study in Plutella xylostella. Small deletions and insertions and consequent premature stop codons in exon 7 were associated with the truncated transcripts at the cDNA level. Analysis of genomic DNA sequences (intron 2 and exons 3–6) failed to detect exon 5 in resistant flies. In addition, a mutation in Bdα6 intron 2, just before the truncated/mis-splicing region and in same location with a mutation previously reported in the Pxylα6 gene, was identified in the resistant flies. RNA editing was investigated but was not found to be associated with resistance. While the demonstration of truncated transcripts causing resistance was outlined, the mechanism responsible for generating truncated transcripts remains unknown.

Identified peptidergic neurons in the Drosophila brain regulate insulin-producing cells, stress responses and metabolism by coexpressed short neuropeptide F and corazonin.

Insulin/IGF-like signaling regulates the development, growth, fecundity, metabolic homeostasis, stress resistance and lifespan in worms, flies and mammals. Eight insulin-like peptides (DILP1-8) are found in Drosophila. Three of these (DILP2, 3 and 5) are produced by a set of median neurosecretory cells (insulin-producing cells, IPCs) in the brain. Activity in the IPCs of adult flies is regulated by glucose and several neurotransmitters and neuropeptides. One of these, short neuropeptide F (sNPF), regulates food intake, growth and Dilp transcript levels in IPCs via the sNPF receptor (sNPFR1) expressed on IPCs. Here we identify a set of brain neurons that utilizes sNPF to activate the IPCs. These sNPF-expressing neurons (dorsal lateral peptidergic neurons, DLPs) also produce the neuropeptide corazonin (CRZ) and have axon terminations impinging on IPCs. Knockdown of either sNPF or CRZ in DLPs extends survival in flies exposed to starvation and alters carbohydrate and lipid metabolism. Expression of sNPF in DLPs in the sNPF mutant background is sufficient to rescue wild-type metabolism and response to starvation. Since CRZ receptor RNAi in IPCs affects starvation resistance and metabolism, similar to peptide knockdown in DLPs, it is likely that also CRZ targets the IPCs. Knockdown of sNPF, but not CRZ in DLPs decreases transcription of Dilp2 and 5 in the brain, suggesting different mechanisms of action on IPCs of the two co-released peptides. Our findings indicate that sNPF and CRZ co-released from a small set of neurons regulate IPCs, stress resistance and metabolism in adult Drosophila.

Larval competition within and between insecticide resistant and susceptible individuals in the oriental fruit fly, Bactrocera dorsalis

AbstractInsecticide resistance is a serious issue in agriculture. Ecological interactions may be used to manage the spread of resistance, but little information is currently available. In particular, virtually none is known about interactions between resistant and susceptible individuals. This study investigated competition between resistant and susceptible oriental fruit fly larvae (Bactrocera dorsalis). Competition in the larval stage was examined with an explicit consideration of individual identity (resistant or susceptible). Guava fruits were inoculated with eggs of susceptible and/or resistant flies, and their development and survival were monitored. Egg density influenced the time that larvae stayed in fruits as well as their survival. In addition, susceptible flies survived better when interacting with resistant flies than with other susceptible flies, indicating that susceptible flies are competitively superior to resistant flies. The results suggest that artificially creating environments that induce competition between susceptible and resistant flies can be useful for the management of insecticide resistance.

Prevention of Apoptosis by Mitochondrial Phosphatase PGAM5 in the Mushroom Body Is Crucial for Heat Shock Resistance in Drosophila melanogaster

The heat shock (HS) response is essential for survival of all organisms. Although the machinery of the HS response has been extensively investigated at the cellular level, it is poorly understood at the level of the organism. Here, we show the crucial role of the mushroom body (MB) in the HS response in Drosophila. Null mutants of the mitochondrial phosphatase Drosophila PGAM5 (dPGAM5) exhibited increased vulnerability to HS, which was reversed by MB-specific expression of the caspase inhibitor p35, and similar vulnerability was induced in wild-type flies by knockdown of MB dPGAM5. Elimination of the MB did not affect the HS response of wild-type flies, but did increase the resistance of dPGAM5-deficient flies to HS. Thus, the MB may possess an apoptosis-dependent toxic function, the suppression of which by dPGAM5 appears to be crucial for HS resistance.

Wolbachia Symbiont Infections Induce Strong Cytoplasmic Incompatibility in the Tsetse Fly Glossina morsitans

Tsetse flies are vectors of the protozoan parasite African trypanosomes, which cause sleeping sickness disease in humans and nagana in livestock. Although there are no effective vaccines and efficacious drugs against this parasite, vector reduction methods have been successful in curbing the disease, especially for nagana. Potential vector control methods that do not involve use of chemicals is a genetic modification approach where flies engineered to be parasite resistant are allowed to replace their susceptible natural counterparts, and Sterile Insect technique (SIT) where males sterilized by chemical means are released to suppress female fecundity. The success of genetic modification approaches requires identification of strong drive systems to spread the desirable traits and the efficacy of SIT can be enhanced by identification of natural mating incompatibility. One such drive mechanism results from the cytoplasmic incompatibility (CI) phenomenon induced by the symbiont Wolbachia. CI can also be used to induce natural mating incompatibility between release males and natural populations. Although Wolbachia infections have been reported in tsetse, it has been a challenge to understand their functional biology as attempts to cure tsetse of Wolbachia infections by antibiotic treatment damages the obligate mutualistic symbiont (Wigglesworthia), without which the flies are sterile. Here, we developed aposymbiotic (symbiont-free) and fertile tsetse lines by dietary provisioning of tetracycline supplemented blood meals with yeast extract, which rescues Wigglesworthia-induced sterility. Our results reveal that Wolbachia infections confer strong CI during embryogenesis in Wolbachia-free (GmmApo) females when mated with Wolbachia-infected (GmmWt) males. These results are the first demonstration of the biological significance of Wolbachia infections in tsetse. Furthermore, when incorporated into a mathematical model, our results confirm that Wolbachia can be used successfully as a gene driver. This lays the foundation for new disease control methods including a population replacement approach with parasite resistant flies. Alternatively, the availability of males that are reproductively incompatible with natural populations can enhance the efficacy of the ongoing sterile insect technique (SIT) applications by eliminating the need for chemical irradiation.

Oviposition and performance in natural hosts in cactophilic Drosophila

The cactus–yeast–Drosophila model system provides an excellent opportunity to investigate the significance of ecological factors in evolution. D. buzzatii and D. koepferae are sister species, with partially overlapping distribution ranges and a certain degree of habitat overlap. The main breeding and feeding resources of D. buzzatii are the decaying cladodes of prickly pears (genus Opuntia), whereas D. koepferae utilizes mainly columnar cacti of the genera Cereus and Echinopsis. These host plants differ in their chemical composition, the microflora associated to the decaying process and patterns of spatial and temporal predictability. The aim of the present work is to investigate host plant selection and utilization of two different cactus hosts. We report the results of field and laboratory studies examining behavioral traits related to egg-laying (oviposition preference and host acceptance) and several measures of performance (viability, developmental time, wing morphology and starvation resistance) in flies reared in the two main host cacti that D. buzzatii and D. koepferae exploit in the studied area: O. sulphurea and E. terschekii. The main conclusion of our study is the clear connection between the distribution of the cactophilic species, D. buzzatii and D. koepferae, and the abundance of the two main natural hosts, which is line with the remarkable influence that cactus hosts impose on larval and adult life history traits and behavioral traits. Overall, the results of field and laboratory work point to the important role of host plant shifts in the evolutionary history of these species.