Mortality rate, reproductive output, and trap response bias in populations of the blowfly Lucilia sericata

1. The ages of 877 females of the blowfly Lucilia sericata, collected from two farms in south-west England between May and September 1996, were determined using a combination of ovarian dissection and wing fray analysis. 2. Using survivorship analysis, the mortality rates over the entire field season were estimated to be 2.2 and 1.9% per day-degree at the two farms, respectively. These gave a mean life expectancy of 46 and 53 day-degrees, and a lifetime reproductive output of 130 and 172 eggs per female. 3. The mortality rate remained relatively constant over time, with one exception, the first sample of the season when no older flies were present, indicating that underlying changes in demography (emergence and senescence of generations) over the field season were not sufficient to affect the rates calculated by survivorship analysis. 4. The response of L. sericata to liver-baited traps was affected strongly by age and reproductive status, with gravid females and females in the early stages of ovarian development being most markedly over-represented relative to other age categories.     

Fly abundance and climate as determinants of sheep blowfly strike incidence in southwest England

The relationships between abundance of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae), climate, animal management procedures and the incidence of cutaneous myiasis (blowfly strike) in sheep were examined in three sheep pasture systems in southwest England during the summers of 2002 and 2003. In each year, flies were collected using liver-baited sticky targets, daily weather and routine husbandry practices were noted and the age-class of each animal infested and body position of each strike were recorded. On sites where no strike control was used, 5.8-12.1% of ewes and 5.7-15.8% of lambs were struck. Ewe strikes predominated at the beginning of the season. The incidence of ewe strikes was significantly associated with higher mean temperature, rainfall and shearing; shearing was associated with a 95% reduction in the risk of ewe strike. In lambs, the incidence of strike was significantly related to higher fly abundance, ewe shearing, treatment and mean ambient temperature. Lambs were 4.6 times more likely to be struck after the ewes had been shorn than before; however, the strongest relationship was with mean L. sericata abundance. Average minimum threshold temperatures of 9.5 degrees C for lamb strikes and 8.5 degrees C for all strikes were extrapolated, below which oviposition did not occur. Over 80% of ewe strikes occurred in the breech region in 2002, as did 100% in 2003. However, in lambs both body and breech strikes occurred in both years. The distribution of lamb strikes appeared to change over time, with breech strikes predominating in May, June and July and body strikes occurring increasingly later in the season. The incidence of lamb breech strikes was significantly associated with higher L. sericata abundance and ewe shearing but there was no relationship with weather conditions. By contrast, the risk of body strike in lambs was significantly associated with higher blowfly abundance, higher rainfall and higher maximum temperatures. The relationship between strike incidence and L. sericata abundance is important because it enhances our understanding of strike incidence patterns and management of this disease. Clearly, any factors that facilitate larger L. sericata populations, such as inappropriate carcass burial or increased average ambient temperatures, are likely to increase the incidence of strike.     

Visual and olfactory cue interaction in resource-location by the blowfly, Lucilia sericata

Abstract. The interactions between olfactory and visual cues in the landing responses of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were examined in a laboratory wind tunnel. The odour of liver and sodium sulphide solution released at 1 L/min, resulted in a greater number of landings, closer to, but downwind of, the central odour release point, than when odour was absent. Three-day-old protein-deprived females landed in greater numbers than protein-fed female flies of the same age; no difference existed between 6-day-old protein-fed or protein-deprived females. Six-day-old, protein-fed flies landed closer to the odour source than did 3-day-old, protein-fed flies. In the presence of odour, flies landed closer to the central release point when it was accompanied by a visual cue. No such effect of the visual cue was evident in the absence of odour. When a plain white sticky-surface (25 × 25 cm) was paired with an identical white surface plus odour, approximately equal numbers of flies landed when the surfaces were placed together; increasingly higher numbers of flies landed on the surface with the odour cue when the distance between the surfaces was increased. When a white surface with a visual cue was presented with the plain white surface plus odour, more flies landed on the white surface with the visual cue than on the plain white surface with odour when they were close together. However, as these two surfaces were moved apart, flies landed increasingly more on the surface with the odour than the surface with the visual cue. The results show that while odour cues may enhance the induction of landing by female L. sericata , visual cues are important when selecting a final landing site.     

Effects of targets impregnated with the chitin synthesis inhibitor triflumuron on the blowfly Lucilia sericata

The effects of exposure of adults of the blowfly Lucilia sericata (Meigen) for 24 h to cloth targets impregnated with the chitin synthesis inhibitor triflumuron plus sucrose or sucrose only, were considered. When both male and female L. sericata were exposed to targets treated with sucrose only, the percentage egg hatch varied between 60–75%. When both sexes were exposed to targets treated with 10% triflumuron plus sucrose the percentage egg hatch varied between 3–7%. When females alone were exposed to triflumuron, prior to the introduction of unexposed males, egg hatch varied between 4–14%. The exposure of males alone to 10% triflumuron treated targets, prior to the introduction of unexposed virgin females, did not give any consistent significant decrease in the mean percentage egg hatch. However, repetition of this trial with males exposed to targets treated with 15 or 20% triflumuron, resulted in a percentage egg hatch of 3.1% and 10.3%, respectively. These results suggest that at relatively high target concentrations, males can transfer effective doses of triflumuron to unexposed virgin females.The exposure of adults to triflumuron treated targets did not significantly increase the mortality of either male or female L. sericata. Furthermore, bioassays showed that there was no significant decline in the ovicidal effectiveness of targets treated with 10% triflumuron and sucrose solution following exposure to sun and rain for up to 8 weeks in 1995 and 1996.The results suggest that targets treated with triflumuron suspension concentrate and sucrose may form the basis of an effective system for the control of L. sericata in the field. However, the relatively high concentrations of triflumuron required and the low efficiency with which males are able to transfer effective doses to unexposed females may diminish one of the main theoretical advantages of using a chitin synthesis inhibitor, such as triflumuron, over a conventional insecticide.     

Suppression of the blowfly Lucilia sericata using odour-baited triflumuron-impregnated targets

Abstract. Field trials were carried out in 1995 and 1996 on farms in the south-west of England to assess the extent to which odour-baited targets could be used to suppress populations of the ectoparasitic blowfly, Lucilia sericata , in sheep pastures. Targets were constructed from 41 × 41 cm squares of aluminium sheet, covered by white cloth which had been dipped in a mixture of sucrose solution (50% w/v) and the chitin synthesis inhibitor triflumuron (10% suspension concentrate). Each target was baited with ≈ 300 g of liver and sodium sulphide solution (10%). Three matched sheep farms were used in the trials. In 1995, triflumuron-impregnated targets were placed around the periphery of sheep pastures at one of the farms in late June, at approximately one target per hectare. In 1996, triflumuron-impregnated targets were placed around the periphery of sheep pastures of a second of the farms in early May, at approximately five targets per hectare. Each year, five sticky targets, used to monitor the L. sericata populations, were also placed in fields at the experimental and the other two farms, which acted as controls. In 1995, the results provided some, although inconclusive, evidence that the triflumuron-impregnated targets had reduced the numbers of L. sericata relative to the populations on the two control farms. In 1996, however, the density of L. sericata on the experimental farm was reduced to almost zero and remained significantly lower than on two control farms throughout the period during which the triflumuron-impregnated targets remained in the field. The results are discussed in relation to the use of triflumuron-treated targets as a practical means of controlling L. sericata and sheep blowfly strike.     

Adult mortality and oviposition rates in field and captive populations of the blowfly Lucilia sericata

Abstract.  1. Adult mortality and oviposition rates were determined for populations of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae). This species is of economic importance as the primary agent of sheep myiasis throughout north-western Europe.
2. Populations of marked flies in six, 1 m³, outdoor field cages and unmarked wild flies at two farms in south-west England were studied simultaneously between May and September 1998.
3. In the field, wild female L. sericata were caught and aged using a combination of wing-fray and ovarian dissection techniques. Survivorship analysis gave estimates of mortality of 1.94% (± 0.037) and 2.09% (± 0.044) per day-degree and mean life expectancy of 51.5 and 47.9 day-degrees above a threshold of 11 °C, at the two farms studied. Mean lifetime reproductive output in the field was estimated to be 159.6 and 138.4 eggs per female at the two farms respectively.
4. The survivorship of cohorts of marked female flies in cages was followed by counting the number of dead individuals each day; the mortality rate of these flies was 0.81% per day-degree (± 3.49 × 10⁻⁴%) and the mean life expectancy was 123.1 day-degrees above a threshold of 11 °C. Mortality rate was shown to increase significantly with average ambient temperature and relative humidity lagged for two sample periods (approximately 10 days). Oviposition rate also increased with average temperature but declined with average relative humidity. A best-fit multiple regression model incorporating both ambient temperature and humidity explained 60.5% of the variance in the pattern of oviposition.
5. The differences between the field and cage populations highlight the caution required when extrapolating life-history parameters from artificial to natural habitats.     

Mitochondrial genomes of the sheep blowfly, Lucilia sericata, and the secondary blowfly, Chrysomya megacephala

This paper presents complete mitochondrial genomes for the sheep blowfly, Lucilia sericata (Meigen), and the secondary blowfly, Chrysomya megacephala (Fabricius). Both L. sericata and C. megacephala had standard dipteran-type mitochondrial genome architectures and lengths of 15 945 bp and 15 831 bp, respectively. Additionally, C. megacephala possessed a tRNA duplication either side of the D-loop, as previously reported in another Chrysomya species, C. putoria; this duplication appears to be synapomorphic for the genus Chrysomya. As in other insect mitochondrial genomes, base compositions had a high AT content, with both genomes more than 76% AT-rich.     

Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike

Abstract.

• 1 The control of ovine myiasis by suppression of populations of the blowfly Lucifia sericata was investigated experimentally on three farms in the south-west of England in 1992 and 1993.
• 2 In blind trials, sheep on one farm (control) were given two doses of placebo, on a second two doses of the larvicide cyromazine (Vetrazin®, CibaGeigy), and on a third cyromazine and a subsequent dose of placebo.
• 3 The first treatment was given shortly before the predicted spring emergence of L.sericata and the second shortly before the predicted emergence of the second generation. Previous simulation analysis had identified strategic early-season treatment as the optimum for blowfly population suppression.
• 4 On both treatment farms significantly smaller L.sericata populations were recorded throughout 1992 and the incidence of strike was significantly lower than on the control farm. The results show that appropriate early-season timing of sheep treatment can suppress populations of L.sericata and could be used by farmers to reduce the incidence of blowfly strike.
• 5 The results suggest, however, that the effectiveness of population suppression and strike incidence may have been influenced by immigration into the control areas and by adverse weather, the latter changing the susceptibility of sheep to strike and resulting in rising strike incidence even when L.sericata population densities were low. In practice, therefore, blowfly population suppression should be employed as a component of an integrated strike management programme.

     

Development and validation of a simulation model for blowfly strike of sheep

A comprehensive simulation model for sheep blowfly strike due to Lucilia sericata (Meigen) (Diptera: Calliphoridae), which builds on previously published versions but also incorporates important new empirical data, is used to explain patterns of lamb and ewe strike recorded on 370 farms in south-west, south-east and central England and Wales. The model is able to explain a significant percentage of the variance in lamb strike incidence in all four regions, and ewe strike in three of the four regions. The model is able to predict the start of seasonal blowfly strike within one week in three of the four regions for both ewes and lambs, and within 3 weeks in the fourth region. It is concluded that the accuracy of the model will allow it to be used to assess the likely efficacy of new control techniques and the effects of changes in existing husbandry practices on strike incidence. The model could also be used to give sheep farmers advance warning of approaching strike problems. However, the ability to forecast future strike patterns is dependent on the accuracy of the weather projections; the more long-term the forecast, the more approximate the prediction is likely to be. When applied on a regional basis, model forecasts indicate expected average patterns of strike incidence and may not therefore be appropriate for individual farmers whose husbandry practices differ substantially from the average.     

Antibacterial properties of larval secretions of the blowfly, Lucilia sericata

The antibacterial properties of secretions aseptically collected from larvae of the greenbottle fly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were examined. These investigations revealed the presence of small (<1 kDa) antibacterial factor(s) within the larval secretions, active against a range of bacteria. These include the Gram-positive Staphylococcus aureus, both methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA), Streptococcus pyogenes and to a lesser extent the Gram-negative Pseudomonas aeruginosa. These secretions were shown to be highly stable as a freeze-dried preparation and, considering the activity against organisms typically associated with clinical infection, may be a source of novel antibiotic-like compounds that may be used for infection control and in the fight against MRSA.     

Development of an attractive target for the sheep blowfly Lucilia sericata

Coloured, odour-baited, sticky targets, designed to catch the sheep blowfly Lucilia sericata Meigen are described and the results of field trials are presented. The number of L. sericata caught by the targets was positively related to target surface area and was dependent on target colour. The performance of the coloured targets is described by a model in which catch is related negatively to reflectivity in the 300-450 nm (ultra-violet/blue) band of the spectrum and positively to the reflectivity in the 450-580 nm (blue-green-yellow) band. Of the Lucilia blowflies caught by the targets, 13-16% were L.sericata and 72-75% of the L.sericata were female. The number of L.sericata caught appeared to be positively related to the availability of sheep over a relatively localized area and showed a marked decline following insecticidal dipping of sheep. The further development of targets and the implications of the results for L.sericata control are discussed.     

Effects of ovarian development and protein deprivation on the activity and locomotor responses of the blowfly, Lucilia sericata, to liver odour

Abstract. The spontaneous activity and locomotor responses to liver odour of females of the blowfly Lucilia sericata Meigen (Diptera: Calliphoridae) were examined in the laboratory using a rocking-box olfactometer. Spontaneous activity levels depended on fly age, previous exposure to protein and recent oviposition history; 1-day-old females, 3-day-old protein-fed females, and females that had recently oviposited exhibited lower levels of spontaneous activity than protein-deprived or fully gravid individuals. Changes in locomotor activity in response to liver odour also depended on previous exposure to protein. In protein-fed flies, activity decreased in response to liver odour and then increased on termination of an odour pulse. This response became more pronounced with age, broadly in line with the expected state of oocyte maturation. This pattern of change was not evident in protein-deprived females. The results are discussed in relation to the relative importance of protein and oviposition-site resources to L. sericata and the resultant age and ovarian development-stage biases evident in field catches.     

The potential for control of the blowfly Lucilia sericata using odour-baited targets

Abstract A deterministic simulation model is used to explore the potential for control of the sheep blowfly, Lucilia sericata , using odour-baited targets. The simulations show that the ambient temperatures of 15^oC or 20^oC, 13% and 24% of the females present in a population would need to be killed per day, respectively, to prevent the population growing from its initial spring density during the summer blowfly season. In contrast, if both sexes could be sterilized, so that sterilized males were also able to disrupt the fertility of unsterilized females, only 6.5–13% of both sexes would need to be attracted and sterilized at 15^oC or 20^oC respectively. To examine whether these numbers of individuals could be attracted by targets baited with liver and sodium sulphide, mark-release-recapture studies in sheep pastures were used to quantify sticky target efficiencies. The percentage of the Lsericata population caught on any one day was shown to be positively related to average ambient temperature. At 15^oC each sticky target caught approximately 13% and at 20^oC, 41% of the females within a 20 m radius. The results indicate that, at ambient temperatures between 15 and 20^oC, if distributed at a density of approximately 5/ha, targets baited with liver and sodium sulphide could effectively suppress a population of L.sericata. Lower densities of targets would be required if they were able to sterilize both sexes rather than kill or if more attractive synthetic semiochemical baits could be developed.     

Isolation and characterization of polymorphic microsatellite markers in the blowflies Lucilia illustris and Lucilia sericata

Thirteen polymorphic microsatellite loci were developed for blowflies for use in studies of genetic differentiation in wild populations of Lucilia illustris, to detect the possible occurrence of bottlenecks and to study changes in genetic variation in laboratory populations of Lucilia sericata following artificial bottlenecks. In this preliminary study it was revealed that heterozygosity was lower than expected in wild populations and genetic variation had been lost in the laboratory population despite being kept at a large size.     

Short-term cold storage of blowfly Lucilia sericata embryos

The developmental rate under low temperatures and cold tolerance were investigated in embryos of the blowfly Lucilia sericata. The larvae of this species are now widely used in maggot debridement therapy. Embryonic development was dependent on temperature, with a lower developmental threshold of 9.0 °C. The duration of the egg stage at a rearing temperature of 25 °C was 14 h, and a low temperature of 12.5 °C successfully prolonged this period to 66 h. Embryonic stages differed markedly in their cold tolerance; young embryos were less tolerant to cold than old ones. Late embryonic stages are suitable for cold storage at 5 °C and the storage for 72 h did not decrease the hatching rate by more than 50%. In the mass‐rearing process required for maggot debridement therapy, either of these two simple protocols would be beneficial.     

Comparison of traps for the control of sheep blowfly in the U.K.

The ability of three commercially available trap types to catch Lucilia (Diptera: Calliphoridae) blowflies was assessed on three sheep farms in southwest England in 2008. The aim was to evaluate their relative value for the control of ovine cutaneous myiasis (sheep blowfly strike) on farms. There was a highly significant difference between the total number of female Lucilia caught per day by the traps, with an Agrilure Trap (Agrimin Ltd, Brigg, U.K.) catching more than the other trap types (Rescue Disposable Fly Trap, Sterling International, Spokane, U.S.A.; Redtop Trap, Miller Methods, Johannesburg, South Africa). However, there was no significant difference between the traps in the numbers of female Lucilia sericata (Meigen) caught. Nevertheless, consideration of the rate at which female L. sericata were caught over time showed that the Agrilure trap did not begin catching until about 30 days after its initial deployment. It subsequently caught L. sericata at a faster rate than the other two traps. The data suggest that the freeze‐dried liver bait used in the Agrilure trap required a period of about 30 days to become fully rehydrated and decompose to the degree required to attract and catch L. sericata. Once the bait was attractive, however, the trap outperformed the other two traps in terms of the rate of L. sericata capture. The Agrilure trap would appear to be the most effective of the designs tested for use against sheep blowfly and blowfly strike in the U.K., but care would be needed to ensure that the traps were deployed in advance of the blowfly season so that the bait was suitably aged when trapping was required.     

Hypersensitivity responses and repeated infections with Lucilia cuprina, the sheep blowfly.

, , and 1992. Hypersensitivity responses and repeated infections with Lucilia cuprina, the sheep blowfly. International Journal for Parasitology 22: 1175–1177. Sheep repeatedly infected with L. cuprina at 2- but not 4-week intervals developed partial resistance to infection after five infections, as measured by larval recovery. However, resistance did not persist for more than three infections. Skin weal responses were measured after injection of larval products simultaneously with each infection. The only correlation between weal size and larval recoveries occurred at infection 1 and indicated a relationship between skin sensitivity and innate rather than acquired resistance. The results suggest that resistance to L. cuprina can develop after repeated infections but that it is short lived and requires frequent larval exposure. A role for hypersensitivity responses was not confirmed by the weal responses but was suggested by the size of wound developed per larva recovered.     

The use of carrion as breeding sites by the blowfly Lucilia sericata and other Calliphoridae

Abstract. To examine the species composition of flies breeding in carrion in the field, the carcasses of mice and quail were exposed on sheep farms in the South West of England. Calliphora vicina was the dominant species of Diptera; 19,294 individuals emerged from 175 of the 241 infested carcasses recovered. Lucilia sericata emerged from only 39 of the infested carcasses, at a median of 10 adults per infested carcass. Other species of Lucilia present were L.ampullacea, L.caesar and L.illustris. The highest number of L.sericata emerged from carcasses placed in open pasture, the highest number of C.vicina emerged from carcasses in hedgerow, whereas the highest numbers of L.caesar, L.ampullacea and L.illustris emerged from carcasses in woodland. The duration of exposure of carcasses in the field was negatively related to the size of the adult L.sericata which emerged and, in woodland and hedgerow habitats, to the number of L.sericata which emerged. These data indicate that the larvae of L.sericata in carcasses experience significant levels of competition and that the intensity of this competition may be sufficient to reduce the numbers of L.sericata able to emerge successfully. The size distributions of female L. sericata which emerged from carcasses or which were caught as adults in the field showed only a small degree of overlap, suggesting that only a relatively small proportion of the wild L.sericata population emerge from carcass breeding sites. The results are discussed in relation to the development of new approaches to the control of blowfly strike of sheep.