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.     

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.     

Expression of lucifensin in Lucilia sericata medicinal maggots in infected environments

Lucifensin, a novel larval defensin, is one of the antibacterial agents of medicinal maggots involved in maggot therapy. The goal of this study was to examine lucifensin expression in various larval tissues during Lucilia sericata development and in maggots exposed to a variety of infectious environments in vitro. In situ hybridisation revealed lucifensin expression in the salivary glands of all larval stages. Expression was occasionally detected in a few cells of the fat body and in the grease coupler of the salivary glands. Expression of lucifensin in the salivary glands was initiated 5–6 h after hatching from the egg. Maximum expression was reached about 24 h after hatching, remained strong during the second and third instars and declined at the end of the third instar, before the wandering stage. Expression of lucifensin was also investigated in maggots after oral ingestion of certain pathogens regularly found in infected chronic wounds. No differences were detected in the salivary glands after stimulation by wound bacterial isolates. However, lucifensin expression was strongly stimulated in the fat body by the presence of Staphylococcus aureus and Pseudomonas aeruginosa. Our data suggest that certain infectious environments increase lucifensin expression only in the fat body, whereas its production and antimicrobial activity in excretion/secretion products are not affected.     

Morphological identification of Lucilia sericata,Lucilia cuprina and their hybrids (Diptera,Calliphoridae)

Hybrids of Lucilia sericata and Lucilia cuprina have been shown to exist in previous studies using molecular methods, but no study has shown explicitly that these hybrids can be identified morphologically. Published morphological characters used to identify L. sericata and L. cuprina were reviewed, and then scored and tested using specimens of both species and known hybrids. Ordination by multi-dimensional scaling indicated that the species were separable, and that hybrids resembled L. cuprina, whatever their origin. Discriminant function analysis of the characters successfully separated the specimens into three unambiguous groups – L. sericata, L. cuprina and hybrids. The hybrids were morphologically similar irrespective of whether they were from an ancient introgressed lineage or more modern. This is the first evidence that hybrids of these two species can be identified from their morphology. The usefulness of the morphological characters is also discussed and photographs of several characters are included to facilitate their assessment.     

Induction of antibacterial activity in larvae of the blowfly Lucilia sericata by an infected environment

Maggot debridement therapy (MDT) is a method for the treatment of intractable, infected and necrotic wounds. In MDT, sterile larvae of Lucilia sericata Meigen (Diptera: Calliphoridae) are applied to infected wounds, where they exert antibacterial effects. Once the larvae are placed in the wound, they are no longer germ-free. This study analysed the influence of infected environments on larval antibacterial activities. Sterile larvae were mixed in a test tube containing a bacterial suspension of Staphylococcus aureus or Pseudomonas aeruginosa, transferred to liver puree agar, and incubated at 25 °C for set periods. To collect the larval extracts, the incubated larvae were transferred to a test tube containing phosphate buffered saline (PBS), cut into multiple pieces with scissors, and centrifuged. The supernatant was used to test antibacterial activities. The results showed that infected larvae had better antibacterial capacities than sterile larvae. Antibacterial activities were induced by pretreatment with a single bacterial species, S. aureus or P. aeruginosa, within 24 h and 12 h, respectively, and disappeared after 36 h. The activities were effective against S. aureus, but not against P. aeruginosa. This natural infection model is very similar to the clinical wound context in MDT and will be a powerful tool with which to study the antibacterial activities of L. sericata larvae in MDT.     

Synomones in necrophagous larvae of the blow flies Lucilia sericata and Calliphora vomitoria

Chemical signals are widespread in insects, but those resulting in interspecific communication (i.e., synomones) remain understudied. Here, we analysed chemicals left on substrates by two species of blow fly larvae, Lucilia sericata (Meigen) and Calliphora vomitoria (Linneaus) (Diptera: Calliphoridae), which can aggregate together on carrion. Using solid-phase microextraction and dynamic headspace analysis, we identified six compounds common to both species: the decanoic, tetradecanoic, pentadecanoic, hexadecanoic and octadecanoic acids, and the 2-ethylhexyl salicylate. We then tested the behavioural effects of the decanoic and pentadecanoic acids using binary-choice experiments, along with the (Z)-9-tricosene, a pheromone found in many arthropods. The time spent by a larva and its average crawling speed were measured in two sides of an arena, where only one contained a compound at 0.25 or 25 μg/μl. No effect was observed when testing the decanoic acid. The pentadecanoic acid only reduced the speed of C. vomitoria larvae at 25 μg/μl. Finally, L. sericata larvae spent less time in the side containing the (Z)-9-tricosene at 0.25 μg/μl, whereas C. vomitoria spent more time and crawled faster in this side at 25 μg/μl. Although these results did not directly evidence synomones, they suggest that the (Z)-9-tricosene could regulate larval aggregations on carrion.     

实时荧光定量PCR中内参基因的选择

实时荧光定量PCR技术是分析基因表达谱的一种常用方法,在分析中选择合适的内参基因对数据进行校正是得到可信数据的关键。以Lactobacillus helveticus H9为研究对象,应用实时荧光定量PCR技术,评价了5种常用内参基因ldh、recA、rpoB、gapdh和16S rRNA的表达稳定性,通过geNorm和NormFinder程序进行数据分析,结果表明5个候选内参基因在菌株不同的发酵时间点表达相对都较为稳定,结合两种分析得到其中最为稳定的基因是ldh,适合于用作后续实时荧光定量PCR试验中的内参基因。     

Asymmetric competition between larvae of the blowflies Calliphora vicina and Lucilia sericata in carrion

1. The relative abundance of the blowflies Calliphora vicina (R.-D.) and Lucilia sericata (Meigen) in carrion was considered in relation to inter- and intraspecific larval competition and the distribution of adults between habitat types. 2. In mixed and pure laboratory cultures of L. sericata and C. vicina the mortality of both species increased and adult size declined as the initial larval number was increased. However, for L. sericata at initial numbers greater than ten larvae/g of liver, the effects of competition on adult size and mortality were greater in the mixed cultures than in the pure cultures. In contrast, for C. vicina at numbers greater than ten larvae/g of liver, the effects of competition on adult size and mortality were greater in the pure cultures than in the mixed cultures. 3. The laboratory data suggest therefore that for L. sericata the effects of interspecific competition with C. vicina on size and mortality were greater than the effects of intraspecific competition in a pure culture at the same initial number. Notably, however, the intensity of interspecific competition was not sufficiently asymmetric to allow C. vicina to exclude L. sericata even at the highest numbers examined. 4. In the field, higher numbers of adult L. sericata emerged from the carcasses of laboratory mice placed in open pasture than in woodland or hedgerow sites. In contrast, higher numbers of C. vicina emerged from carcasses placed in woodland and hedgerow sites. 5. Trapping showed that in the field adult L. sericata were relatively more abundant in open pasture than in woodland and hedgerow sites, while C. vicina were more abundant in woodland and hedgerow sites than in open pasture. 6. It is concluded that the low numbers of L. sericata that emerge from carrion relative to the numbers of C. vicina may, in part, be the result of asymmetric interspecific competition, but that the uneven distribution of adults of the two species among habitat types also plays a major role in shaping the blowfly community in carrion.     

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.     

基因表达研究中内参基因的选择与应用

管家基因是一类无组织特异性的,在物种的所有组织细胞中都表达的基因,被广泛用作内参基因来检测目标基因在不同的组织器官、一定的发育阶段或胁迫的环境条件下的表达规律变化。这些管家基因并不是在所有生理条件下都能作为理想内参基因稳定表达。在基因表达转录分析中,大多数普遍使用的内参基因已不能满足准确定量的要求。基于统计学分析软件,如geNorm、BestKeeper和NormFinder三种分析软件,可以筛选出稳定性较好的内参基因。本文综述了内参基因的选择条件、方法及应用。     

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.     

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.

     

A comparison of Lucitraps and sticky targets for sampling the blowfly Lucilia sericata

The Lucitrap (Miazma Pty Ltd, Queensland, Australia) combined with a synthetic odour bait, Lucilure (Miazma Pty Ltd, Queensland, Australia), is a commercially available trap for sampling and control of Lucilia cuprina (Wiedemann) in Australia. It was tested in Hungary against Lucilia sericata (Meigen) (Diptera: Calliphoridae), a cause of sheep strike throughout temperate Europe. The standard Lucitrap was tested against black or yellow sticky target traps. Both trap types were baited with either Lucilure or liver and 10% w/v sodium sulphide solution. With Lucilure as bait, L. sericata were caught on sticky traps but not in Lucitraps. With liver and sodium sulphide as bait, sticky traps caught 500-1500 times more L. sericata than Lucitraps. An adhesive sheet fitted to the top of a Lucitrap captured 30-300 times more L. sericata then were captured inside an unaltered Lucitrap. Direct observation of metallic green calliphorids (92.1% L. sericata) alighting on Lucitraps indicated that most flies stayed for a short while (modal class 2-4 s) and only a few stayed longer, to an observed maximum of 28 s. Flies explored a mean of 1.5 entry holes (range 0-7) during a visit but only 6% entered the trap. Size of L. sericata was not a physical barrier to Lucitrap entry, because many larger species were captured. However, L. sericata captured inside Lucitraps were significantly smaller than those captured on sticky traps, demonstrating that size was of behavioural importance. The data demonstrate that the Lucitrap is not effective as a trap for L. sericata in Hungary, due mainly to a failure of flies to enter the trap in large numbers. In Australia and South Africa, L. sericata is commonly caught in Lucitraps baited with Lucilure, although L. cuprina is more numerous. Our study highlights the potential for diversity of fly behaviour between different geographical populations of the same species. Such diversity can have a significant effect on the functioning of systems for fly sampling and control, when these systems depend for their success on certain behavioural responses of the target species.