High levels of insecticide resistance in introduced horn fly (Diptera: Muscidae) populations and implications for management

The horn fly, Haematobia irritans (L.) (Diptera: Muscidae), was introduced to Chile in the beginning of the 1990s. Since its introduction, farmers have controlled this pest almost exclusively with insecticides. To understand the consequences of different control strategies on the development of insecticide resistance and their persistence, a field survey was conducted at eight farms in the south of Chile to characterize insecticide resistance in field populations and resistance mechanisms. Horn fly samples were assayed to determine levels of resistance to pyrethroids and diazinon, genotyped for kdr and HialphaE7 mutations, and tested for general esterase activity. All field populations, including ones that were not treated with insecticides for the past 5 yr, showed high levels of cypermethrin resistance and high frequencies of the kdr mutation. None of the fly populations demonstrated resistance to diazinon and the HialphaE7 mutation was not detected in any of the fly samples. Esterase activities in all populations were comparable to those found in the susceptible reference strain. The findings of high frequencies of homozygous resistant and heterozygous individuals both in insecticide treated horn fly populations and in the untreated fly populations suggests complex interactions among field populations of the horn fly in Chile.     

Biotypes of Hessian fly (Dipt., Cecidomyiidae) in Morocco

Hessian fly, Mayetiola destructor (Say), is the most important insect pest of wheat in Morocco, where host plant resistance has been used successfully for control. Our objective was to determine the frequency of Hessian fly virulence on H5, H13 and H22 resistance genes. Five Hessian fly populations from the principal cereal‐growing regions in Morocco were studied. The variability in percentage of susceptible plants across Hessian fly populations was highly significant (P < 0.01), indicating differences in virulence frequencies. Plants with the H13 gene had the lowest percentage of susceptible plants, 1.77 and 1.51%, when infested with Hessian flies from Fes and Marchouch, respectively. A low level of virulence to H22 was detected in Fes, Abda and Marchouch populations, 1.87, 1.54 and 1.99% susceptible plants, respectively. The level of virulence to H5 was low in all the five populations. The Beni Mellal population gave the highest percentage of susceptible plants carrying H13 and H22 genes, 6.43 and 7.28%, respectively. The size of live larvae on susceptible plants of the three cultivars carrying H5, H13 and H22 was similar to that of the susceptible check, indicating that a true virulence (biotype) is developing in Hessian fly populations in Morocco. Thus, continuous monitoring of the development of Hessian fly biotypes is essential for optimal deployment of resistance genes.     

Genetics of organophosphate resistance in field populations of the house fly (Diptera: Muscidae)

The genetics of resistance to the organophosphate insecticide diazinon were investigated in four populations of the house fly, Musca domestica L., collected in the southern United States. Crosses were made between individual females of lines derived from each population and males of a susceptible strain with three recessive mutants on chromosome II. Individual F1 females were crossed to mutant males, and the progenies were scored for resistance to diazinon and for the presence of mutant phenotypes. A major chromosome II gene for resistance to diazinon was present in all populations at an overall frequency of 83%. Map distances between the resistance gene and the mutant aristapedia and between the mutants aristapedia and stubby wing were highly variable in all populations. Recombination among the visible mutants was usually reduced in resistant progenies relative to susceptible progenies. The data suggest that a single major gene for resistance to diazinon was present on chromosome II in all test populations at variable map positions and is usually associated with a chromosome rearrangement, probably an inversion. The results are similar to those obtained earlier with house fly populations selected for resistance to insecticides in the laboratory; therefore, they seem to be characteristic of field and laboratory populations of the house fly. Overall, the data offer an explanation for previous results suggesting the existence of multiple, closely linked genes for metabolic resistance to insecticides on house fly chromosome II.     

Dynamics of cypermethrin resistance in the field in the horn fly,Haematobia irritans

The toxicity of cypermethrin to the horn fly Haematobia irritans (L.) (Diptera: Muscidae) was determined for samples collected from untreated herds at a farm in central Argentina from October 1997 to May 2001. Field tests of the efficacy of cypermethrin against horn flies were first carried out at this farm in 1993, when the fly was shown to be susceptible to pyrethroids. Subsequently the horn fly populations on this farm were shown to have become resistant and, since 1997, the use of cypermethrin has been restricted to experimental purposes. In this study, fly samples collected in 1999, 2000 and 2001 were subjected to a polymerase chain reaction (PCR) to detect the presence of a specific nucleotide substitution in the sodium channel gene sequence, which has been associated with target site insensitivity to pyrethroids. This analysis showed that the level of cypermethrin resistance had diminished between 1997 and 2001. However, this was not sufficient to restore the efficacy of this pyrethroid to the level found prior to the onset of resistance. Heterozygous and homozygous resistant flies were detected in all samples of flies subjected to PCR diagnosis of alleles conferring target site resistance.     

Post-colonization temporal genetic variation of an introduced fly, Rhagoletis completa

Evolutionary biologists have been puzzled by the success of introduced species: despite founder effects that reduce genetic variability, invasive species are still successful at colonizing new environments. It is possible that the evolutionary processes during the post-colonization period may increase the genetic diversity and gene flow among invasive populations over time, facilitating their long-term success. Therefore, genetic diversity and population structure would be expected to show greater temporal variation for successful introduced populations than for native populations. We studied the population genetics of the walnut husk fly, Rhagoletis completa, which was introduced into California from the Midwestern US in the early 1900s. We used microsatellites and allozymes to genotype current and historic fly populations, providing a rare perspective on temporal variability in population genetic parameters. We found that introduced populations showed greater temporal fluctuations in allele frequencies than native populations. Some introduced populations also showed an increase in genetic diversity over time, indicating multiple introductions had occurred. Population genetic structure decreased in both native and introduced populations over time. Our study demonstrates that introduced species are not at equilibrium and post-colonization processes may be important in ameliorating the loss of genetic diversity associated with biological invasions.     

Genetic variation among populations of the Hessian fly Mayetiola destructor (Diptera: Cecidomyiidae) in Morocco and Syria

The RAPD-PCR technique was used to study genetic variation within and among geographical populations of the Hessian fly, Mayetiola destructor (Say), from Morocco and Syria, associated with the fly's ability to overcome resistance in three wheat cultivars containing H5, H13 and H22 resistance genes. Variation was detected both for the level of susceptibility of the cultivars and RAPD profiles of M. destructor populations. By the use of RAPD-PCR, high genetic variability was detected among individuals and populations of M. destructor within and between areas separated geographically. The DNA fingerprints of populations of M. destructor were area-specific with Nei's measures of genetic distance ranging from 0.156 (between Abda and Beni Mellal, Morocco) to 1.977 (between Marchouch, Morocco and Lattakia, Syria). Cluster analysis of the genetic distances among the populations, identified the Syrian population as an outlier. A highly significant correlation (r = 0.81) observed between the genetic and geographic distances among the populations, provided genetic support for dispersal of the fly from its presumed origin in West Asia to Morocco.     

Invasion genetics of American cherry fruit fly in Europe and signals of hybridization with the European cherry fruit fly

The American cherry fruit fly is an invasive pest species in Europe, of serious concern in tart cherry production as well as for the potential to hybridize with the European cherry fruit fly, Rhagoletis cerasi L. (Diptera: Tephritidae), which might induce new pest dynamics. In the first European reports, the question arose whether only the eastern American cherry fruit fly, Rhagoletis cingulata (Loew) (Diptera: Tephritidae), is present, or also the closely related western American cherry fruit fly, Rhagoletis indifferens Curran. In this study, we investigate the species status of European populations by comparing these with populations of both American species from their native ranges, the invasion dynamics in German (first report in 1993) and Hungarian (first report in 2006) populations, and we test for signals of hybridization with the European cherry fruit fly. Although mtDNA sequence genealogy could not separate the two American species, cross‐species amplification of 14 microsatellite loci separated them with high probabilities (0.99–1.0) and provided evidence for R. cingulata in Europe. German and Hungarian R. cingulata populations differed significantly in microsatellite allele frequencies, mtDNA haplotype and wing pattern distributions, and both were genetically depauperate relative to North American populations. The diversity suggests independent founding events in Germany and Hungary. Within each country, R. cingulata displayed little or no structure in any trait, which agrees with rapid local range expansions. In cross‐species amplifications, signals of hybridization between R. cerasi and R. cingulata were found in 2% of R. cingulata individuals and in 3% of R. cerasi. All putative hybrids had R. cerasi mtDNA indicating that the original between‐species mating involved R. cerasi females and R. cingulata males.     

Genetic diversity at electrophoretic loci in the house fly,Musca domestica L.

Vertical polyacrylamide gel electrophoresis was used to separate enzyme proteins at 73 putative loci in natural house fly populations sampled in central Iowa. Thirty-nine of the loci were polymorphic (53%). The mean effective number of alleles per polymorphic locus was 1.93 and 1.47 alleles among 68 scored loci. Observed and expected heterozygosities at 34 house fly loci were 0.1628 and 0.1834, respectively. No statistically significant differentiation was detected among nine central Iowa fly populations in 1989 or among nine Iowa and three Minnesota populations in 1990. Journal Paper No. J-14125 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 2949.     

Allatostatin-like immunoreactivity in the optic lobe of the fly Sarcophaga bullata.

An antiserum against Diploptera allastostain 1 (Dip-AST1) was used to map the distribution of allatostain containing neurons in the optic lobes of the fly Saccrophaga bullata. Strongly immunoreacting neurons were found in two areas of the optic ganglia, namely, the medulla and the area between medulla and lobula. These cells were generally interneurons arborizing the base of the medulla. The positive reaction of specific populations of the optic lobe neurons against allatostain antiserum suggests some role for this neuropeptide in the visual physiology of the fly.     

Lifespan of a Ceratitis fruit fly increases with higher altitude

Variation in lifespan may be linked to geographic factors. While latitudinal variation in lifespan has been studied for a number of species, altitude variation has received much less attention, particularly in insects. We measured the lifespan of different populations of the Natal fruit fly Ceratitis rosa along an altitudinal cline. For the different populations we first measured the residual longevity of wild flies by captive cohort approach and compared F(1) generation from the same populations. We showed an increase in lifespan with higher altitude for a part of our data. For the field collected flies (F0) the average remaining lifespan increased monotonically with altitude for males but not for females. For the F(1) generation, longevity of both males and females of the highest-altitude population was longer than for the two other lower-altitude populations. This relationship between altitude and lifespan may be explained by the effects of temperature on reproduction. Reproductive schedules in insects are linked to temperature: lower temperature, characteristic of high-altitude sites, generally slows down reproduction. Because of a strong trade-off between reproduction and longevity, we therefore observed a longer lifespan for the high- altitude populations. Other hypotheses such as different predation rates in the different sites are also discussed.     

Microsatellite analysis reveals remating by wild Mediterranean fruit fly females,Ceratitis capitata

Accurate estimates of remating in wild female insects are required for an understanding of the causes of variation in remating between individuals, populations and species. Such estimates are also of profound importance for major economic fruit pests such as the Mediterranean fruit fly (Ceratitis capitata). A major method for the suppression of this pest is the sterile insect technique (SIT), which relies on matings between mass-reared, sterilized males and wild females. Remating by wild females will thus impact negatively on the success of SIT. We used microsatellite markers to determine the level of remating in wild (field-collected) Mediterranean fruit fly females from the Greek Island of Chios. We compared the four locus microsatellite genotypes of these females and their offspring. Our data showed 7.1% of wild females remated. Skewed paternity among progeny arrays provided further evidence for double matings. Our lowest estimate of remating was 3.8% and the highest was 21%.     

Pyrethroid and organophosphate pesticide resistance in field populations of horn fly in Brazil

Pesticides are used worldwide to control arthropod parasites in cattle herds. The indiscriminate and/or inappropriate use of pesticides without veterinary guidance is a reality in several countries of South America. Improper pesticide use increases the chances of contamination of food and the environment with chemical pesticides and their metabolites. Reduction of these contamination events is an increasing challenge for those involved in livestock production. The horn fly, Haematobia irritans (Linnaeus) (Diptera: Muscidae), is one of the most economically important parasites affecting cattle herds around the world. As such, horn fly control efforts are often required to promote the best productive performance of herds. Pesticide susceptibility bioassays revealed that pyrethroid resistance was widespread and reached high levels in horn fly populations in the Brazilian state of Rondônia. The knockdown resistance (kdr) sodium channel gene mutation was detected in all horn fly populations studied (n = 48), and the super kdr sodium channel gene mutation was found in all homozygous resistant kdr individuals (n = 204). Organophosphate resistance was not identified in any of the fly populations evaluated.     

Horn fly (Diptera: Muscidae) insecticide resistance in Kentucky and Arkansas

The effect of previous insecticide use patterns for horn fly control on the susceptibility spectrum of horn fly (Haematobia irritans [L.]) populations from Kentucky and Arkansas is described. Populations of horn flies from both states were tested with three pyrethroids (cyhalothrin, cypermethrin, and permethrin), three organophosphates (diazinon, pirimiphos methyl, and tetrachlorvinphos), and a chlorinated hydrocarbon (methoxychlor). Dose-mortality data indicated insecticide resistance in Arkansas and Kentucky. Two permethrin-resistant horn fly populations in Kentucky that did not have a history of exposure to methoxychlor were cross-resistant to this chlorinated hydrocarbon. Horn fly populations from both states with a history of at least three consecutive years of exposure to various pyrethroid ear tags were subsequently exposed to cattle tagged with cyhalothrin-impregnated ear tags for 15-16 wk. Such exposure resulted in a decrease in susceptibility to this pyrethroid (ranging from approximately 30 to greater than 100-fold) when compared with levels before treatment. Horn fly populations from Arkansas resistant to cyhalothrin (as a result of exposure to cyhalothrin ear tags) were cross-resistant to pirimiphos methyl. Seasonal exposure of an Arkansas and Kentucky horn fly population to cattle with ear tags impregnated with pirimiphos methyl resulted in a significant decrease in susceptibility to this organophosphate.     

Emergence of flies from overwintering populations of cabbage root fly pupae

ABSTRACT.

• 1 Once pupal diapause had been terminated, over-wintering cabbage root fly (Delia radicum (L.)) pupae from Wellesbourne required a further 14 days at 20°C for most of the flies to emerge.
• 2 There were considerable variations in the rates of fly emergence from thirteen populations of cabbage root fly pupae collected between latitudes 50° 42′ and 54° 59′ in England and Wales. These thirteen populations could be grouped into early-, intermediate- and late-emerging types. In the early-emerging type, flies emerged within 14 days at 20°C whereas in the late-emerging type emergence was protracted and was completed only after 100 days at 20°C in one population from Halsall, Lancashire. In the intermediateemerging type, approximately two-thirds of the flies emerged within 14 days at 20° C, the remainder taking considerably longer.
• 3 The intermediate-emerging types could be just mixtures of the early- and late-emerging types.
• 4 Subjecting pupae to diapause-breaking temperatures (4°C) for up to 1 year failed to shorten the time to subsequent fly emergence in any of the populations.
• 5 Populations of early, intermediate- and late-emerging fies could be selected from a parental population, heterogeneous with respect to emergence, within one generation.
• 6 The type of emergence that occurred in a locality was not correlated with latitude.
• 7 Any models developed for forecasting the most appropriate time to apply insecticide in a locality will have to include information about the emergence pattern of the fly population in that locality.

     

Prevalence of Candidatus Erwinia dacicola in wild and laboratory olive fruit fly populations and across developmental stages

The microbiome of the olive fruit fly, Bactrocera oleae (Gmelin), a worldwide pest of olives (Olea europaea L.), has been examined for >100 yr as part of efforts to identify bacteria that are plant pathogens vectored by the fly or are beneficial endosymbionts essential for the fly's survival and thus targets for possible biological control. Because tephritid fruit flies feed on free-living bacteria in their environment, distinguishing between the transient, acquired bacteria of their diet and persistent, resident bacteria that are vertically transmitted endosymbionts is difficult. Several culture-dependent and -independent studies have identified a diversity of species in the olive fruit fly microbiome, but they have not distinguished the roles of the microbes. Candidatus Erwinia dacicola, has been proposed to be a coevolved endosymbiont of the olive fruit fly; however, this was based on limited samples from two Italian populations. Our study shows that C. Erwinia dacicola was present in all New and Old World populations and in the majority of individuals of all life stages sampled in 2 yr. Olive fruit flies reared on olives in the laboratory had frequencies of C. Erwinia dacicola similar to that of wild populations; however, flies reared on artificial diets containing antibiotics in the laboratory rarely had the endosymbiont. The relative abundance of C. Erwinia dacicola varied across development stages, being most abundant in ovipositing females and larvae. This uniform presence of C. Erwini dacicola suggests that it is a persistent, resident endosymbiont of the olive fruit fly.     

Parasites that attack stable fly and house fly (Diptera: Muscidae) puparia during the winter on dairies in northwestern Florida

Throughout the winter and early spring months, stable fly, Stomoxys calcitrans (L.), and house fly, Musca domestica L., puparia were collected from silage, hay, and manure from six dairies in northwestern Florida and evaluated for parasitism. Of the puparia producing flies or parasites, 23% of the stable flies and 46% of the house flies were parasitized. The predominant parasite observed attacking muscoid flies (76% for stable flies and 58% for house flies) was Spalangia cameroni Perkins. Muscidifurax sp. was recovered from 11 and 36% of the stable fly and house fly pupae, respectively. Other parasite species encountered were Spalangia endius Walker and S. nigroaenea Curtis. Significantly more parasitized fly pupae were collected from silage than from hay residues or manure. Winter and early spring parasite populations in northwestern Florida appear to be present as long as viable fly pupae are available to support the developing parasites.     

Seasonal abundance of the stable fly Stomoxys calcitrans in southwest England

The stable fly Stomoxys calcitrans (L.) is a cosmopolitan biting fly of both economic and welfare concern, primarily as a result of its painful bite, which can cause blood loss, discomfort and loss of productivity in livestock. Between June and November in 2016 and May and December in 2017, Alsynite sticky‐traps were deployed at four Donkey Sanctuary sites in southwest England, which experience recurrent seasonal biting fly problems. The aim was to evaluate the seasonal dynamics of the stable fly populations and the risk factors associated with abundance. In total, 19 835 S. calcitrans were trapped during the study period. In both years, abundance increased gradually over summer months, peaking in late August/September. There were no relationships between seasonally detrended abundance and any climatic factors. Fly abundance was significantly different between sites and population size was consistent between years at three of the four sites. The median chronological age, as determined by pteridine analysis of flies caught live when blood‐feeding, was 4.67 days (interquartile range 3.8–6.2 days) in males and 6.79 days (interquartile range 4.8–10.4 days) in females; there was no significant, consistent change in age or age structure over time, suggesting that adult flies emerge continuously over the summer, rather than in discrete age‐related cohorts. The data suggest that flies are more abundant in the vicinity of active animal facilities, although the strong behavioural association between flies and their hosts means that they are less likely to be caught on traps where host availability is high. The implications of these results for fly management are discussed.     

Bot fly parasitism of the red-backed vole: host survival,infection risk,and population growth

Parasites can play an important role in the dynamics of host populations, but empirical evidence remains sparse. We investigated the role of bot fly (Cuterebra spp.) parasitism in red-backed voles (Myodes gapperi) by first assessing the impacts of the parasite on the probability of vole survival under stressful conditions as well as on the reproductive activity of females. We then identified the main factors driving both the individual risk of infection and the abundance of bot flies inside red-backed voles. Finally, we evaluated the impacts of bot fly prevalence on the growth rate of vole populations between mid-July and mid-August. Thirty-six populations of red-backed voles were sampled in the boreal forest of Québec, Canada. The presence and the abundance of parasites in voles, two host life history traits (sex and body condition), three indices of habitat complexity (tree basal area, sapling basal area, coarse woody debris volume), and vole abundance were considered in models evaluating the effects of bot flies on host populations. We found that the probability of survival of red-backed voles in live traps decreased with bot fly infection. Both the individual risk of infection and the abundance of bot flies in red-backed voles were driven mainly by vole abundance rather than by the two host life history traits or the three variables of habitat complexity. Parasitism had population consequences: bot fly prevalence was linked to a decrease in short-term growth rate of vole populations over the summer. We found that bot flies have the potential to reduce survival of red-backed voles, an effect that may apply to large portions of populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mitochondrial haplotypes reveal olive fly (Bactrocera oleae) population substructure in the Mediterranean

The olive fly (Bactrocera oleae) is the most important olive tree (Olea europaea) pest. In the Mediterranean basin, where 98?% of its main hosts are concentrated, it causes major agricultural losses, due to its negative effect on production and quality of both olive and olive oil. Previous phylogeographic analyses have established that Mediterranean olive fly populations are distinct from other Old World populations, but did not agree on the specific population substructure within this region. In order to achieve a higher resolution of the diversity of olive fly populations, particularly in Central and Western Mediterranean (home to 70?% of the world production), we comparatively analyzed a set of samples from Portugal in the context of published mitochondrial sequences across the species' worldwide range. Strong evidence of population substructure was found in the Central and Western Mediterranean area, with two clearly separate phylogenetic branches. Together with previously published data, our results strongly support the existence of at least three distinct Mediterranean populations of the olive fly, raise the possibility of additional regional substructure and suggest specific avenues for future research. This knowledge can be instrumental in the development of better management and control strategies for a major pest of Mediterranean agriculture.     

The evolution of Hessian fly from the Old World to the New World: Evidence from molecular markers

Eighteen polymorphic microsatellite loci and 11 single‐nucleotide polymorphisms were genotyped in 1 095 individual Hessian fly specimens representing 23 populations from North America, southern Europe, and southwest Asia. The genotypes were used to assess genetic diversity and interrelationship of Hessian fly populations. While phylogenetic analysis indicates that the American populations most similar to Eurasian populations come from the east coast of the United States, genetic distance is least between (Alabama and California) and (Kazakhstan and Spain). Allelic diversity and frequency vary across North America, but they are not correlated with distance from the historically documented point of introduction in New York City or with temperature or precipitation. Instead, the greatest allelic diversity mostly occurs in areas with Mediterranean climates. The microsatellite data indicate a general deficiency for heterozygotes in Hessian fly. The North American population structure is consistent with multiple introductions, isolation by distance, and human‐abetted dispersal by bulk transport of puparia in infested straw or on harvesting equipment.