A standardised restriction fragment length polymorphism (RFLP) method for typing Mycobacterium avium isolates links IS901 with virulence for birds

A standardised method for PvuII-PstI-IS901 restriction fragment length polymorphism (RFLP) typing was developed and evaluated against 173 isolates of Mycobacterium avium subsp. avium and M. avium subsp. silvaticum originating from birds (N=46) and their aviaries (N=5), pigs (N=85), cattle (N=18), reference serotype strains (N=9), humans (N=7), a horse (N=1), a nutria (N=1), and strain M. avium subsp. avium ST 18 (formerly M. avium subsp. paratuberculosis ST 18). PvuII-IS1245 RFLP typing was also performed on all isolates. DNA was digested in parallel by restriction endonucleases PvuII or PstI and hybridised to standard probes prepared by PCR. DNA fingerprints were scanned by CCD camera and analysed by the Gel Compar (Applied Maths, Version 4.1, Kortrijk, Belgium) software using a standard isolate control profile. A total of 52 PvuII-PstI RFLP profiles was described including 25 PvuII RFLP profiles designated A to Y and 25 PstI RFLP profiles designated A1-L3. Profiles were found to be stable in vivo and in vitro after multiple subcultures. High IS901 copy number was associated with a "bird" PvuII-IS1245 RFLP profile and low IS901 copy number with M. avium subsp. avium isolates from humans and the nutria. A virulence assay of 100 IS901-positive isolates using intramuscular infections of pullets showed 83 isolates differentiated into 32 RFLP types to be virulent and 17 isolates differentiated into 12 RFLP types as nonvirulent. Attenuation of virulence for pullets could be attributed to either multiple in vitro subculture, polyclonal infection or human passage and was not related to IS901 or IS1245 profiles.     

Potential risk of Mycobacterium avium subspecies paratuberculosis spread by syrphid flies in infected cattle farms

The syrphid Eristalis tenax Linnaeus (Diptera: Syrphidae) may be found in and around dung storage pits at cattle farms at various developmental stages of their life cycle. The purpose of this study was to investigate the occurrence of Mycobacterium avium ssp. paratuberculosis in 1044 E. tenax samples at various developmental stages, as well as fresh and stored dung originating from nine cattle farms. Mycobacterium fortuitum was isolated from one (1.5%) larva from the vicinity of three paratuberculosis-free herds of cattle. Mycobacterium a. paratuberculosis was isolated from 111 (21.4%) of E. tenax larvae collected from two of seven farms known to be infected with the causal agent of paratuberculosis. Mycobacteria were not isolated from any of the 340 pupae, 41 adults of 78 samples of exoskeletal exuviae. Mycobacterium a. paratuberculosis isolates from E. tenax larvae were of the IS900 restriction fragment length polymorphism (RFLP) type B-C1, identical to that detected in faecal samples from cattle herds infected with paratuberculosis. Larvae artificially infected with mycobacteria of IS900 RFLP type B-C9 did not contain statistically more CFU of identical IS900 RFLP type B-C9 in the intestinal tract and internal organs than on the body surface. These results show that M. a. paratuberculosis can survive in the intestinal tract and internal organs of E. tenax.     

Detection of Mycobacterium avium subsp. paratuberculosis in two brown bears in the central European Carpathians

The incidence of mycobacterial infections was monitored in brown bears (Ursus arctos) in the National Park Low Tatras in the central European Carpathians in Slovakia. Tissue samples of 20 brown bears were examined microscopically and by culture for the presence of mycobacteria. Acid-fast rods were detected by Ziehl-Neelsen staining in a smear from the kidney of one brown bear, although the culture was negative for mycobacteria. Mycobacterium avium subsp. paratuberculosis, the causative agent of paratuberculosis in ruminants, was isolated from the intestinal mucosa of another two brown bears. The isolates were identified by polymerase chain reaction for the specific insertion sequence IS900. Using standardized IS900 restriction fragment length polymorphism (RFLP) analysis, the M. a. paratuberculosis isolates were classified as RFLP type B-C1, which also were detected in the infected cattle in surrounding area. This study describes the first isolation of M. a. paratuberculosis from a brown bear. Our results confirm that animal species other than ruminants can become infected with M. a. paratuberculosis and can act as potential vectors and/or reservoirs of the infection.     

Infections caused by Mycobacterium avium subspecies avium, hominissuis, and paratuberculosis in free-ranging red deer (Cervus elaphus hippelaphus) in Austria, 2001-2004

Between 2001 and 2004, 14 Austrian free-ranging red deer (Cervus elaphus hippelaphus) infected by Mycobacterium avium species were observed. Eight of the cases were from different geographical regions, and six originated from the same hunting area. The affected animals had signs of diarrhea, severe weight loss, and emaciation. On post-mortem examination, lymphadenitis associated with grossly enlarged mesenteric lymph nodes as well as multiple caseous or purulent nodular lesions in the thickened wall of the intestines were present in all animals. In 10 cases M. avium subsp. avium and in four cases M. a. hominissuis were isolated. In three red deer, a mixed infection with M. a. hominissuis and M. a. paratuberculosis was evident. Typing of M. a. avium and M. a. hominissuis isolates was performed by polymerase chain reaction (PCR) detection of insertion sequence IS901 and the virulence-associated macrophage-induced gene (mig), inverted repeat (IR) typing (IS1245/IS1311), and random amplified polymorph DNA (RAPD) analysis. While all M. a. avium and M. a. hominissuis contained the mig gene, IS901 was detected only in M. a. avium. The prevalence of IS901-positive isolates correlated well with the geographic location of affected animals. The IS901-containing isolates were shown to be genotypically closely related, as they exhibit similar patterns in IR-typing and in RAPD analysis. In contrast, IS901-negative isolates (M. a. hominissuis) displayed distinct profiles in both molecular systems.     

Identification of members of Mycobacterium avium species by Accu-Probes, serotyping, and single IS900, IS901, IS1245 and IS901-flanking region PCR with internal standards

From Mycobacterium avium species Mycobacterium avium subsp. paratuberculosis (n=961), Mycobacterium a. avium (n=677), Mycobacterium a. silvaticum (n=5), and Mycobacterium a. hominissuis (n=1566) were examined, and from Mycobacterium tuberculosis complex M. tuberculosis (n=2), Mycobacterium bovis (n=13), M. bovis BCG (n=4), and Mycobacterium caprae (n=10) were examined. From other mycobacterial species Mycobacterium intracellulare (n=60) and atypical mycobacteria (n=256) including Mycobacterium fortuitum, Mycobacterium chelonae, Mycobacterium scrofulaceum, Mycobacterium gastri and other species of conditionally pathogenic mycobacteria were analysed. The internal standard molecules corresponding to insertion sequences IS900, IS901, IS1245, and flanking region (FR300) of IS901 were produced by PCR of alfalfa genome segment and inserted into plasmid vector. The resulting recombinant plasmid molecules were used as internal standards in coamplification with a total of 4729 mycobacterial collection strains and field isolates between 1996 and 2003. The size differences between amplicons obtained from IS900 (258 bp), IS901 (1108 bp), IS1245 (427 bp), and FR300 (300 bp) and from corresponding internal standard molecules ISIS900 (591 bp), ISIS901 (1 336 bp), ISIS1245 (583 bp), and IS901 flanking region of 300 bp ISFR300 (488 bp), respectively, allowed easy discrimination. The internal amplicons were visible by naked aye on agarose gel when 10(1), 10(3), 10(2), and 10(2) molecules for ISIS900, ISIS901, ISIS1245, and ISFR300 were used in the PCR, respectively, when no bacterial DNA was added to the reaction. The system was tested to define the amount of internal standards that could be used in the PCR without affecting the amplification of the specific segment. Non-specific amplifications were observed in M. fortuitum with IS1245 PCR and mixed infections with M. a. avium and M. a. hominissuis from pigs and cattle were found. PCR results of typing were compared with serotyping and Accu-Probes analyses in selected field isolates.     

Diptera as vectors of mycobacterial infections in cattle and pigs

Mycobacteria were isolated from 14 (4.5%) of 314 samples, containing 7791 adult Diptera, which were collected in the Czech Republic and Slovakia in 1997-2000. These flies were collected from three cattle herds with paratuberculosis, two pig herds with mycobacterial infections and one farm that kept both cattle and pigs and that did not have problems of mycobacterial infections. Mycobacterium intracellulare was isolated from Eristalis tenax Linnaeus (Diptera: Syrphidae) captured from a pig herd. Mycobacterium avium ssp. avium (serotype 8) was isolated from flies of the genera Drosophila Fallen (Diptera: Drosophilidae) and Musca Linnaeus (Diptera: Muscidae) originating from a pig herd. Mycobacterium spp. were isolated from Musca spp. and Mycobacterium fortuitum was isolated from dung flies of the genus Scatophaga Meigen (Diptera: Scatophagidae), Musca spp. and Stomoxys calcitrans Linnaeus (Diptera: Muscidae) captured in the same herd. Mycobacterium scrofulaceum was isolated from S. calcitrans from the farm with both cattle and pigs. Mycobacterium avium ssp. paratuberculosis was isolated from Scatophaga spp. collected from pastures grazed by one of the cattle herds and from Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) and Lucilia caesar Linnaeus (Diptera: Calliphoridae) captured in a slaughterhouse, where cattle infected with paratuberculosis were slaughtered. Mycobacterium phlei was isolated from flies of the genus Lucilia captured at a waste bin. These data indicate that mycobacteria may be spread by adult flies that have been in contact with material contaminated with these pathogens.     

Findings of mycobacteria in insectivores and small rodents

The organs of 30 insectivorous mammals and 62 rodents from areas inhabited by people or livestock where cattle paratuberculosis or mycobacterial infections of swine had been found to occur were examined by cultivation during the monitoring of occurrence and spread of mycobacterioses in cattle and swine. Mycobacteria were found in the organs of 3 insectivores (10%) and 6 rodents (9.7%). Mycobacterium chelonae was isolated from the organs of the lesser white-toothed shrew (Crocidura suaveolens) and the common vole (Microtus arvalis), and M. vaccae and M. avium subsp. avium (IS901+, serotype 1) from the organs of the common shrew (Sorex araneus). M. avium subsp. avium (IS901+, serotype 1) was also isolated from the organs of the yellow-necked mouse (Apodemus flavicollis). Slow-growing mycobacteria of group III (according to Runyon) were isolated from the organs of the mouse (Mus musculus sensu lato) and the yellow-necked mouse (A. flavicollis). These findings had no connection with the epizootological situation in the nearby livestock. M. fortuitum was isolated from the organs of the common vole (M. arvalis) caught in a field within easy reach of a swine breeding herd. M. fortuitum was also identified in the lymph nodes and droppings of this swine herd, as well as in the straw, scrapings from the floor of stalls, troughs and banisters, as well as from larvae and imagoes of dipterous insects. These results demonstrate the possibility that insectivores and small rodents can spread the causative agents of mycobacteria in wild and domestic animals.     

IS901, a new member of a widespread class of atypical insertion sequences, is associated with pathogenicity in Mycobacterium avium

An insertion sequence (IS901), found in pathogenic strains of Mycobacterium avium, but absent in M. avium complex isolates from patients with acquired immune deficiency syndrome (AIDS), has been isolated and sequenced. This insertion element has a nucleotide sequence of 1472 bp, with one open reading frame (ORF1), which codes for a protein of 401 amino acids. The amino acid sequence, terminal ends and target site of IS901 are similar to those of IS900, present in Mycobacterium paratuberculosis. However, the DNA sequences of these two IS elements exhibit only 60% homology, compared to a DNA homology of 98% between their respective hosts. IS901, like IS900, appears to belong to a family of related insertion elements present in actinomycetes and other bacteria. M. avium strains containing IS901 were found to be more virulent in mice than closely related strains lacking IS901. IS901 may be a useful tool for the study of the genetics of virulence in the M. avium complex and for obtaining stable integration of foreign genes into mycobacteria.     

Genotypic characterization of Mycobacterium avium strains recovered from animals and their comparison to human strains.

Mycobacterium avium was recovered from 21 birds and 10 pigs. Bird isolates carried IS901 and a few copies of IS1245 and appeared highly related by pulsed-field gel electrophoresis. Pig isolates showed features previously described in human isolates: a lack of IS901, a high copy number of IS1245, and marked polymorphism by pulsed-field gel electrophoresis.     

Isolation and diagnostic potential of ISMav2, a novel insertion sequence-like element from Mycobacterium avium subspecies paratuberculosis

A novel Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) specific insertion sequence has been identified by representational difference analysis and designated as ISMav2. ISMav2 has no similarity to known mycobacterial IS elements but shows more than 50% identity to a non-composite transposon of Streptomyces coelicolor at the DNA and protein level. ISMav2 is present in at least three copies on the genome as assessed by Southern blot analysis and its potential value as a diagnostic tool was confirmed by PCR analyses on 79 M. paratuberculosis field isolates, nine M. avium ssp. avium isolates, and the reference strains of nine other mycobacterial species.     

Suspicion of Mycobacterium avium subsp. paratuberculosis transmission between cattle and wild-living red deer (Cervus elaphus) by multitarget genotyping

Multitarget genotyping of the etiologic agent Mycobacterium avium subsp. paratuberculosis is necessary for epidemiological tracing of paratuberculosis (Johne's disease). The study was undertaken to assess the informative value of different typing techniques and individual genome markers by investigation of M. avium subsp. paratuberculosis transmission between wild-living red deer and farmed cattle with known shared habitats. Fifty-three M. avium subsp. paratuberculosis type II isolates were differentiated by short sequence repeat analysis (SSR; 4 loci), mycobacterial interspersed repetitive-unit-variable-number tandem-repeat analysis (MIRU-VNTR; 8 loci), and restriction fragment length polymorphism analysis based on IS900 (IS900-RFLP) using BstEII and PstI digestion. Isolates originated from free-living red deer (Cervus elaphus) from Eifel National Park (n = 13), six cattle herds living in the area of this park (n = 23), and five cattle herds without any contact with these red deer (n = 17). Data based on individual herds and genotypes verified that SSR G2 repeats did not exhibit sufficient stability for epidemiological studies. Two common SSR profiles (without G2 repeats), nine MIRU-VNTR patterns, and nine IS900-RFLP patterns were detected, resulting in 17 genotypes when combined. A high genetic variability was found for red deer and cattle isolates within and outside Eifel National Park, but it was revealed only by combination of different typing techniques. Results imply that within this restricted area, wild-living and farmed animals maintain a reservoir for specific M. avium subsp. paratuberculosis genotypes. No host relation of genotypes was obtained. Results suggested that four genotypes had been transmitted between and within species and that one genotype had been transmitted between cattle herds only. Use of multitarget genotyping for M. avium subsp. paratuberculosis type II strains and sufficiently stable genetic markers is essential for reliable interpretations of epidemiological studies on paratuberculosis.     

Characterisation of IS901 integration sites in the Mycobacterium avium genome

Data are presented on the identification and characterisation of 17 chromosomal integration loci of the insertion element IS901 in the Mycobacterium avium (cervine strain JD88/118) genome. Thirteen of these integration loci have been mapped to their corresponding positions on the M. avium strain 104 (an IS901(-) strain) genome (The Institute for Genome Research (TIGR) unfinished genome-sequencing project). Sequence data for both upstream and downstream sequence flanking regions were obtained for 12 insertion loci, while upstream sequence was obtained for five others. A consensus IS901 insertion target sequence compiled from all 17 integration sites was in broad agreement with earlier reports that were based on only two such loci. Analysis of IS901 integration site flanking sequences revealed that, like IS900 in M. avium subspecies paratuberculosis, IS901 inserts preferentially between a putative ribosome-binding sequence (RBS) and the translational start codon of an open reading frame (ORF). In BLAST X and BLAST P searches of the GenBank database, these ORFs were shown to share significant homologies with a number of other prokaryotic genes.     

Standardisation of restriction fragment length polymorphism analysis for Mycobacterium avium subspecies paratuberculosis.

DNA from 1008 strains of Mycobacterium avium subspecies paratuberculosis, digested by restriction endonucleases PstI and BstEII, was hybridised with a standard IS900 probe prepared by PCR and labelled non-radioactively by ECL. DNA fingerprints were scanned by CCD camera and analysed using the software Gel Compar (Applied Maths, Kortrijk, Belgium). Thirteen restriction fragment length polymorphism (RFLP) (PstI) types were detected, which where designated as A, B, C, D, E, F, G, H, I, J, K, L and M in accordance with the study of Pavlik et al. (1995) [Pavlik, I., Bejckova, L., Pavlas, M., Rozsypalova, V., Koskova, S., 1995. Characterization by restriction endonuclease analysis and DNA hybridization using IS900 of bovine, ovine, caprine and human dependent strains of Mycobacterium paratuberculosis isolated in various localities. Vet. Microbiol. 45, 311-318]. Twenty RFLP (BstEII) types were detected and designated as C1-3, C5, C7-20, S1 and I1 in accordance with the study by Collins et al. 1990 [Collins, D.M., Gabric, D.M., de Lisle, G.W., 1990. Identification of two groups of Mycobacterium paratuberculosis strains by restriction endonuclease analysis and DNA hybridization. J. Clin. Microbiol. 28, 1591-1596]. A combination of both RFLP (PstI) and RFLP (BstEII) results revealed a total of 28 different RFLP types. All the RFLP types and detailed protocols are available at Intemet web site WWW...: http:/ /www.vri.cz/wwwrflptext.htm.     

Nymphs of the Oriental cockroach (Blatta orientalis) as passive vectors of causal agents of avian tuberculosis and paratuberculosis

The potential transmission of the causal agent of paratuberculosis Mycobacterium avium ssp. paratuberculosis and avian tuberculosis Mycobacterium avium ssp. avium (Actinomycetales: Mycobacteriaceae) by nymphs of the Oriental cockroach Blatta orientalis L. (Blattodea: Blattidae) was investigated by oral infection with mycobacterial suspensions and examination of their droppings and bodies. Both the subspecies of M. avium were isolated from droppings at 3 days post-infection and M. a. avium was found in homogenized bodies at 10 days post-infection. The identity of M. a. avium and M. a. paratuberculosis isolates was demonstrated by Restriction Fragment Length Polymorphism (RFLP) analysis. The M. a. avium isolate used as the inoculum and the isolates from the bodies and droppings of the nymphs were shown to be virulent in chickens. The results show that orally infected nymphs of B. orientalis can harbour and shed viable and virulent mycobacteria. This hazard should be considered in the implementation of control measures against mycobacterial infections of animals and humans, which should include destruction of all developmental stages of cockroaches and prevention of their access to materials that can be contaminated by mycobacteria.     

Isolation of Mycobacterium avium subsp. paratuberculosis from free-ranging birds and mammals on livestock premises

Surveys for Mycobacterium avium subsp. paratuberculosis infection in free-ranging mammals and birds were conducted on nine dairy and beef cattle farms in Wisconsin and Georgia. Specimens were collected from 774 animals representing 25 mammalian and 22 avian species. Specimens of ileum, liver, intestinal lymph nodes, and feces were harvested from the larger mammals; a liver specimen and the gastrointestinal tract were harvested from birds and small mammals. Cultures were performed by using radiometric culture and acid-fast isolates were identified by 16S/IS900/IS1311 PCR and mycobactin dependency characteristics. M. avium subsp. paratuberculosis was cultured from tissues and feces from 39 samples from 30 animals representing nine mammalian and three avian species. The prevalence of infected wild animals by premises ranged from 2.7 to 8.3% in Wisconsin and from 0 to 6.0% in Georgia. Shedding was documented in seven (0.9%) animals: three raccoons, two armadillos, one opossum, and one feral cat. The use of two highly polymorphic short sequence repeat loci for analysis of 29 of the 39 strains identified 10 alleles. One allelic pattern broadly shared in domestic ruminants ("7,5") appeared in approximately one-third of the wildlife M. avium subsp. paratuberculosis isolates studied. Given the few cases of shedding by free-ranging animals compared to the volume of contaminated manure produced by infected domestic ruminant livestock, contamination of the farm environment by infected wildlife was negligible. Wildlife may, however, have epidemiological significance for farms where M. avium subsp. paratuberculosis recently has been eliminated or on farms free of M. avium subsp. paratuberculosis but located in the geographic vicinity of farms with infected livestock.     

Seasonal and spatial changes in blowfly production from small and large carcasses at Durham in lowland northeast England

Colonization by blowflies (Diptera: Calliphoridae) of mouse carcasses exposed in open agricultural land near Durham (54 45'N) changed from early spring monopolization by Calliphora vicina R.-D. to a summer pattern of multiple species exploitation by this species together with Lucilia caesar L., L. illustris Mg., L. silvarum Mg., L. sericata Mg. and L. richardsi Collin. In a garden at the edge of Durham, mouse carcasses were dominated by C. vicina from spring to autumn. Difference in mouse colonization between the agricultural and garden sites seemed to reflect differences in the blowfly species present, as measured by baited trap catches at the sites. In sets of C. vicina reared from mice under conditions of competition for larval food, it was found that resulting females were significantly larger than males, size being measured as mean wing length. Blowfly production from three sheep carcasses exposed successively at the agricultural site was dominated by C. vomitoria L. and L. caesar, but also produced other Lucilia species in small numbers, including L. sericata. These L. sericata females from sheep that had died from causes other than myiasis included full-sized specimens, in contrast to those produced from mouse carcasses that were all undersized individuals. As L. sericata females trapped on sheep pastures are predominantly full-sized, this suggests that large carcasses may, in part, be a source of the L. sericata population that attacks sheep as a myiasis agent. The nature of large carcasses as possible sources of L. sericata in lowland Britain is discussed.     

PCR comparison of Mycobacterium avium isolates obtained from patients and foods.

Mycobacterium avium is a cause of disseminated disease in AIDS patients. A need for a better understanding of possible sources and routes of transmission of this organism has arisen. This study utilized a PCR typing method designed to amplify DNA segments located between the insertion sequences IS1245 and IS1311 to compare levels of relatedness of M. avium isolates found in patients and foods. Twenty-five of 121 food samples yielded 29 mycobacterial isolates, of which 12 were M. avium. Twelve food and 103 clinical M. avium isolates were tested. A clinical isolate was found to be identical to a food isolate, and close relationships were found between two patient isolates and two food isolates. Relatedness between food isolates and patient isolates suggests the possibility that food is a potential source of M. avium infection. This study demonstrates a rapid, inexpensive method for typing M. avium, possibly replacing pulsed-field gel electrophoresis.     

An IS900-like sequence found in a Mycobacterium sp. other than Mycobacterium avium subsp. paratuberculosis

The insertion sequence IS900 has been considered specific for Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) and has, therefore, been used as the target gene for diagnostic PCR of M. paratuberculosis. From a healthy dairy cow we have isolated and characterised a mycobacterium harbouring one copy of a sequence with 94% identity to IS900 at the nucleic acid level. The isolate was shown to be related to Mycobacterium cookii, as assessed by 16S rRNA sequencing. Strong amplifications were obtained with several PCR primers described for detection of IS900. This finding shows the need of alternative PCR systems based on other genes than IS900 to confirm the presence of M. paratuberculosis.     

Mycobacterium avium subsp. paratuberculosis and M. avium subsp. avium are independently evolved pathogenic clones of a much broader group of M. avium organisms

Mycobacterium avium comprises organisms that share the same species designation despite considerable genomic and phenotypic variability. To determine the degree and nature of variability between subspecies and strains of M. avium, we used multilocus sequencing analysis, studying 56 genetically diverse strains of M. avium that included all described subspecies. In total, 8,064 bp of sequence from 10 gene loci were studied, with 205 (2.5%) representing variable positions. The majority (149/205) of these variations were found among M. avium subsp. hominissuis organisms. Recombination was also evident in this subspecies. In contrast, there was comparatively little variability and no evidence of recombination within the pathogenic subspecies, M. avium subsp. paratuberculosis, M. avium subsp. avium, and M. avium subsp. silvaticum. Phylogenetic analysis showed that M. avium subsp. avium and M. avium subsp. silvaticum strains clustered together on one branch, while a distinct branch defined M. avium subsp. paratuberculosis organisms. Despite the independent origin of these pathogenic subspecies, an analysis of their rates of nonsynonymous (dN) to synonymous (dS) substitutions showed increased dN/dS ratios for both: 0.67 for M. avium subsp. paratuberculosis and 0.50 for M. avium subsp. avium/M. avium subsp. silvaticum, while the value was 0.08 for M. avium subsp. hominissuis organisms. In conclusion, M. avium subsp. hominissuis represents a diverse group of organisms from which two pathogenic clones (M. avium subsp. paratuberculosis and M. avium subsp. avium/M. avium subsp. silvaticum) have evolved independently.     

Lifetime reproductive output of Calliphora vicina and Lucilia sericata in outdoor caged and field populations; flight vs. egg production?

Females of the blowflies Calliphora vicina (Robineau-Desvoidy) and Lucilia sericata (Meigen) (Diptera: Calliphoridae) maintained in sheltered outdoor cages and supplied with excess food, oviposited later than would have been expected from the temperature-sum. The survival rates of the caged flies was high and the isolation of flies from predation, extreme temperatures and food shortages is likely to have contributed to this. Despite good survival rates, subsequent egg production over the greater part of the adult life span was reduced to approximately 24% for C. vicina and approximately 55% for L. sericata, of the potential expected from the published temperature-sums required for the maturation of successive egg batches. The data suggest that under field-cage conditions there is a considerable variation in egg development between individuals of the same age and that this variation should not be overlooked, since it may have significant implications in ecological and forensic investigations; however, the cause of this variability remains unclear. While lower than expected, the reproductive outputs recorded in the cages were nevertheless considerably greater than those that have been estimated for blowflies in the field and illustrate the potential for population increase in these species under favourable conditions. The possibility of a greater energy investment in flight activity relative to reproductive output in C. vicina compared to L. sericata is proposed.