Complex competitive interactions in four species of Lucilia blowflies

Abstract.

• 1 The effects of intraspecific and interspecific larval competition on larval survival, adult size, adult longevity and fecundity were quantified in four species of coexisting Lucilia blowflies: illustris, silvarum, sericata and caesar.
• 2 There was a general negative effect of increasing density on larval and adult survival, size and fecundity. Additionally, complex species-specific and frequency-dependent responses were identified, which were not expected in these biologically and morphologically closely similar species.
• 3 Lucilia illustris, the numerically dominant species in the natural community, was a superior competitor to L.silvarum at intermediate densities but an inferior competitor at high density. Such nonlinear responses may be related to differences in the life histories and larval behaviour of the species (bigger eggs and more contest-type outcome of competition in L.silvarum).
• 4 We parameterized a model of interspecific competition on a subdivided resource in an attempt to reconcile the conflicting results on larval competitive abilities and the abundances of the species in the field. Using laboratory and field-estimated parameter values the model predicted coexistence of L.illustris and L.silvarum and the observed numerical dominance of the former species. The average densities of flies in the field are limited to relatively low levels, apparently preventing L.silvarum (the superior competitor at high density) from dominating and excluding L. illustris.

     

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.     

THE CONTROL OF BLOWFLIES INFESTING SLAUGHTER-HOUSES I. FIELD OBSERVATIONS OF THE HABITS OF BLOWFLIES

The habits of blowflies infesting slaughter-houses have been studied to determine the conditions under which control measures are most likely to be effective. Flies found in such numbers as to be considered pests of economic importance were: Calliphora erythrocephala (Meig.) and C. vomitoria (L.); Lucilia caesar (L.), L. illustris (Meig.) and L. sericata (Meig.); and Phormia terrae-novae (R.-D.). All were found breeding profusely on slaughter-house refuse.
The reactions of adult blowflies to weather and the working conditions at the slaughter-house are recorded; the three genera react in differing degrees to relatively minor changes in weather conditions, and redistribution of populations caused by these changes is so rapid as to make difficult the accurate assessment of degree of infestation. It was found that blowflies normally do not settle on the internal fabric of slaughter-house buildings but tend rather to congregate on nearby vegetation. The preferences were studied of adult flies for certain types of meat, for particular parts of carcasses, and for meat exposed to sunlight.
Conditions favouring rapid development of larvae were determined and the rates of breeding recorded for the three genera when in natural competition and when breeding independently. The larvae of P. terrae-novae were found to be predacious on other species and each other. Lucilia sericata was found to oviposit and breed successfully in vegetable matter.
Blowflies overwinter as fully grown larvae which pupate only a short while before emerging in the spring.
Various methods are discussed whereby the findings of this investigation into the life history and habits of blowflies can be utilized in the control of these pests.     

The structure of carrion fly communities: the size and the type of carrion

Species composition and abundance relations of flies attracted to and bred from different sizes (20-100 g) and types of carrion (small mammal, cow liver, bird, and fish) were studied experimentally in natural breeding conditions in South Finland. Large pieces of carrion did not attract significantly more individuals or species than did small ones, but there was a positive correlation between size of carrion and numbers of flies bred, apparently because of competition. Altogether 10 species emerged from 50 cultures, and on average 2.78 ± 1.22 (SD) species emerged from one culture. The number of co-occurrences among the emerging flies indicated random colonization. Variation in species composition between like pieces of carrion was not less than variation between carcasses of different size or type; hence, size and type of carrion are not important determinants of community structure within the size and type ranges used.
Lucilia illustris (Meig.) was the predominant species, comprising 50% of flies trapped and 85% of flies bred. The difference indicates changing species composition in the community. Two sets of cultures were left open for egg-laying for 2 and 7 d. Competition was less Intensive in the former cultures, which produced 4.0 individuals per gram of carrion, contrasting with only 1.4 individuals per gram in the latter cultures. Competition delayed development in all species, but least in L. illustris , which suggests that fast developing species are at a competitive advantage. In agreement with this, abundance was positively correlated with the rate of development.     

Community structure of carrion flies along an island gradient

species richness, abundance relations, exploitation efficiencies, and population dynamics were examined within four carrion fly communities from a small isolated island in the Baltic to the large island of Åland. A total of 23 species and 11408 Specimens were collected.
Species richness (studied by rarefaction) of potential carrion flies was lowest on the small isolated island, but the smallest number of species emerged from the second largest island. Lucilia illustris Meig, was the most numerous species at every site, comprising 46–56% of the potential breeders and 71–91% of the emerging flies. Exploitation efficiency, measured by the numbers of individuals emerging per gram of carrion, was highest on the smallest island, but faunal similarity and ordination analyses suggest that competition was more intense on the larger islands.     

Competition in variable environments: experiments with planktonic rotifers

1. In a constant environment, competition often tends to reduce species diversity. However, several theories predict that temporal variation in the environment can slow competitive exclusion and allow competing species to coexist. This study reports on laboratory competition experiments in which two pairs of planktonic rotifer species competed for a phytoplankton resource under different conditions of temporal variability in resource supply.
2. For both species pairs, Keratella cochlearis dominated under all conditions of temporal variability, and the other species ( Brachionus calyciflorus or Synchaeta sp.) almost always went extinct. Increasing temporal variation in resource supply slowed competitive exclusion but did not change competitive outcome or allow coexistence.
3. Rotifers show a gleaner–opportunist trade-off, because gleaner species have low threshold resource levels ( R *) and low maximum population growth rates, while opportunist species have the opposite characteristics. In the competition experiments, the gleaner always won and the opportunists always lost. Thus, a gleaner–opportunist trade-off was not sufficient to facilitate coexistence under conditions of resource variability. Instead, the winning species had both the lowest R * and the greatest ability to store resources and ration their use during times of extreme resource scarcity.     

Spatial and temporal habitat partitioning by calliphorid blowflies

Calliphorid blowflies perform an essential ecosystem service in the consumption, recycling and dispersion of carrion nutrients and are considered amongst the most important functional groups in an ecosystem. Some species are of economic importance as facultative agents of livestock myiasis. The interspecific ecological differences that facilitate coexistence within the blowfly community are not fully understood. The aim of this work was to quantify differences in habitat use by calliphorid species. Thirty traps were distributed among three habitats at two sites in southwest England for collections made during March–August 2016. A total of 17 246 specimens were caught, of which 2427 were Lucilia sericata, 51 Lucilia richardsi, 6580 Lucilia caesar, 307 Lucilia ampullacea, 4881 Calliphora vicina and 2959 Calliphora vomitoria (all: Diptera: Calliphoridae). Lucilia sericata was the dominant species in open habitats, whereas L. caesar was the most abundant species in shaded habitats. Calliphora specimens were more abundant in the cooler months. These findings suggest that Calliphora and Lucilia species show strong temporal segregation mediated by temperature, and that species of the genus Lucilia show differences in the use of habitats that are likely to be driven by differences in humidity tolerance and light intensity. These factors in combination result in effective niche partitioning.     

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.     

Myiasis by Lucilia silvarum (Calliphoridae) in amphibian species in boreal Alberta, Canada

We report myiasis by Lucilia silvarum with an overall prevalence of 0.9% in amphibian populations in boreal Alberta. In the period 1998--1999, we documented L. silvarum infestations in wild populations of wood frog (Rana sylvatica), boreal chorus frog (Pseudacris maculata), boreal toad (Bufo boreas boreas), and Canadian toad (B. hemiophrys). We believe this is the first record of this parasite from boreal and Canadian toads. Almost all previous records of L. silvarum parasitism in North America indicate that myiasis is fatal to an anuran host. Here, we provide the first record of adult individuals from 2 species (wood frog and boreal toad) surviving infestations. Although we actively captured and examined amphibians in Alberta from 1996 to 2006, we only found parasitism in 1998 and 1999. This is the most northerly record of anuran infestations by this parasite.     

Spatial and temporal variability of necrophagous Diptera from urban to rural areas

The spatio-temporal variability of necrophagous fly assemblages in a linear series of habitats from central London to the rural surroundings in the south-west was studied using bottle traps between June 2001 and September 2002. A total of 3,314 individuals in 20 dipteran families were identified from 127 sampling occasions. Calliphoridae accounted for 78.6% of all the dipteran specimens, with Calliphora vicina Robineau-Desvoidy, being the most abundant species (2,603 individuals, 46.9%). Using canonical correspondence analyses (CCA) on 72 fly taxa, six sampled sites and 36 environmental variables, three habitat types corresponding to three groups of flies were identified. These were an urban habitat characterized by C. vicina, Lucilia illustris (Meigen) and L. sericata (Meigen), a rural grassland habitat, characterized by L. caesar (Linnaeus) and a rural woodland habitat characterized by Calliphora vomitoria (Linnaeus), Phaonia subventa (Harris), Neuroctena anilis (Fallén) and Tephrochlamys flavipes (Zetterstedt). Intermediate species (L. ampullacea Villeneuve and P. pallida (Fabricius), located between the three habitats, were also found. Temporal abundance of the 10 most abundant species showed fluctuations between seasons, having low numbers of captured individuals during winter. Correspondence analysis showed clearly seasonal patterns at Box Hill site. The species-habitat associations suggest habitat differentiation between necrophagous guilds in this area and may be of ecological value.     

Differential susceptibility to variable plant phenology and its role in competition between two insect herbivores on oak

Abstract. 1. The population dynamics of Tortix viridana L. (Lepidoptera: Tortricidae) and Operophtera brumata L. (Lepidoptera: Geometridae) on the pedunculate oak Quercus robur L. are driven by the degree to which larval hatch coincides with oak budburst in spring.
2. Experiments with first instar larvae demonstrate that T. viridana has a much narrower dietary breadth, is less inclined to disperse from closed oak buds, and can resist starvation for longer periods than the polyphagous O.brumata.
3. As a result of its specialist foraging strategy, T. viridana may be less susceptible to mortality associated with colonization of oak in spring than O.brumata. This may explain why T. viridana populations are, on average, higher.
4. These results are discussed in the light of previous work which described the competitive advantage of O. brumata in field cage experiments. Stochastic mortality factors, which drive population change in both species independently of competition, favour T.viridana larvae, and over-ride the competitive superiority of O.brumata.     

The life cycles and growth of Carabus glabratus and C. violaceus in Budalen, central Norway

Abstract. 1. The seasonal activity patterns of adults and larvae, and the seasonal development of female gonads showed that Curubus glabrafus Payk. and Curubus violaceus L. living in a subalpine habitat are spring (summer) breeders with biennial life cycles.
2. As a rule, the adults and third stage larvae hibernate, but C.glubrutus at least can hibernate also at the second larval stage, particularly in years in which unfavourable climatic conditions in the spring delay breeding.
3. The adaptive strategies underlying these life history patterns and their possible significance for species diversification and coexistence are discussed.     

Can host‐range allow niche differentiation of invasive polyphagous fruit flies (Diptera: Tephritidae) in La Réunion?

Abstract.  1. Biological invasions bring together formerly isolated insect taxa and allow the study of ecological interactions between species with no coevolutionary history. Among polyphagous insects, such species may competitively exclude each other unless some form of niche partitioning allows them to coexist.
2. In the present study, we investigate whether the ability to exploit different fruits can increase the likelihood of coexistence of four species of polyphagous Tephritidae, one endemic and three successive invaders, in the island of La Réunion. In the laboratory, we studied the performances of all four species on the four most abundant fruit resources in the island, as well as the relative abundances of fly species on these four fruit species in the field. We observe no indication of niche partitioning for any of the four abundant fruits.
3. Analyses of an extensive field data series suggest that: (i) the four fly species largely overlap in fruit exploitation, once climatic effects are accounted for; (ii) however, one species ( Ceratitis capitata ) can exploit rare fruit species that are not exploited by others present in the same climatic niche; and (iii) the endemic species C. catoirii , now nearly extinct in La Réunion, has no private niche with respect to either climatic range or fruit use.
4. On the whole, with the possible exception of C. capitata , the results point to a limited role of fruit diversity in encouraging coexistence among polyphagous tephritids recently brought into contact by accidental introductions.     

Crop domestication disrupts a native tritrophic interaction associated with the sunflower, Helianthus annuus (Asterales: Asteraceae)

Abstract.  1. Crop domestication has been a largely overlooked factor that may explain why insect herbivores tend to be more abundant and less attacked in agricultural habitats than in native habitats. This study explores how domestication of the sunflower, Helianthus annuus L., affects the sunflower moth, Homoeosoma electellum (Lepidoptera: Pyralidae), and its parasitoids.
2. Common garden experiments were used to assess the effect of domestication on larval abundance in an agricultural and a native habitat. The effect of domestication on parasitism was determined using two studies: one study that manipulated nitrogen according to levels found in agricultural and native habitats, and a second common garden study in the native habitat.
3. At peak infestation in the agricultural common garden, larval abundance was 10 times higher on agricultural plants than on wild plants. In contrast, larval abundance did not differ between plant genotypes in the native habitat.
4. Larvae were four times more likely to be parasitised on wild sunflowers than on agricultural sunflowers, and three times more likely to be parasitised on low nitrogen plants than on high nitrogen plants. Parasitism did not differ between agricultural and wild plants in the native habitat, where flowers were more similar in size.
5. Sunflower domestication has increased larval abundance, accelerated larval development, and lowered parasitism. The magnitude of the effect appears to depend upon nutrient availability. Thus, domestication can disrupt tritrophic interactions, and may help explain why some insect pests are more abundant and less attacked in agro-ecosystems.     

The Male Accessory Gland Substances of Lucilia illustris (I): Its Effect on Mating Receptivity

ABSTRACT In order to verify the physiological functions of male accessory gland (MAG) substances of the blowfly, Lucilia illustris Meigen, the growth and changes in metabolites of male accessory gland with aging, and the effect of male accessory gland extract on mating receptivity of L. illustris were examined. There was not a significant difference in length of MAG with aging, but the width of MAG was grown widely from 0 to 5-days old apparently. Changes in glycogen, total protein and lipid of male accessory gland substances showed same patterns but total protein content was higher than the others. Therefore, male nutrition affected the production of male accessory proteins. During the mating fed unmated male transferred larger amount of protein than that of starved male. When male accessory gland homogenates injected, mating receptivity of gravid female was greatly inhibited comparing to control, suggesting that the accessory gland substances of L. illustris alters female mating receptivity after mating.     

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.     

Revision of ilyphagus chamberlin, 1919 (polychaeta, flabelligeridae)

Ilyphagus Chamberlin, 1919 includes abyssal, fragile benthic species. Most species have large cephalic cages but chaetae are brittle and easily lost which may explain why the original definition included species with a cephalic cage or without it. The type species, Ilyphagus bythincola Chamberlin, 1919, together with another species (Ilyphagus pluto Chamberlin, 1919) were described as lacking a cephalic cage whereas a third species (Ilyphagus ascendens Chamberlin, 1919) was described with one. To clarify this situation, all available type and non-type materials were studied. Ilyphagus is redefined to include species with digitiform bodies, abundant filiform papillae and a thin body wall; their neurochaetae are thick, anchylosed aristate spines, and all species have a cephalic cage (in the type species the presence of a cage is inferred from the remaining chaetal scars). Ilyphagus pluto, which also lacks a a cephalic cage is determined here to be a holothurian. The redefined genus contains Ilyphagus bythincola (incl. Ilyphagus ascendens), Ilyphagus coronatus Monro, 1939, Ilyphagus hirsutus Monro, 1937, and Ilyphagus wyvillei (McIntosh, 1885).     

Maggot therapy: a review of the therapeutic applications of fly larvae in human medicine, especially for treating osteomyelitis

In traditional medical practice, the larvae of some Diptera: Calliphoridae, notably Lucilia illustris (Meigen), L.sericata (Meigen) and Phormia regina (Meigen), have been employed for maggot therapy, i.e. to help clean lesions antiseptically, especially for treatment of chronic osteomyelitis. This mode of treatment remains appropriate for cases where antibiotics are ineffective and surgery impracticable.     

Reciprocal intraguild predation and predator coexistence

Intraguild predation is a mix of competition and predation and occurs when one species feeds on another species that uses similar resources. Theory predicts that intraguild predation hampers coexistence of species involved, but it is common in nature. It has been suggested that increasing habitat complexity and the presence of alternative food may promote coexistence. Reciprocal intraguild predation limits possibilities for coexistence even further. Habitat complexity and the presence of alternative food are believed to promote coexistence. We investigated this using two species of predatory mites, Iphiseiodes zuluagai and Euseius concordis, by assessing co‐occurrence in the field and on arenas differing in spatial structure in the laboratory. The predators co‐occured on the same plants in the field. In the laboratory, adults of the two mites fed on juveniles of the other species, both in the presence and the absence of a shared food source, showing that the two species are involved in reciprocal intraguild predation. Adults of I. zuluagai also attacked adults of E. concordis. This suggests limited possibilities for coexistence of the two species. Indeed, E. concordis invariably went extinct extremely rapidly on arenas without spatial structure with populations consisting of all stages of the two predators and with a shared resource. Coexistence was prolonged on host plant leaves with extra food sources, but E. concordis still went extinct. On small, intact plants, coexistence of the two species was much longer, and ended with the other species, I. zuluagai, often going extinct. These results suggest that spatial structure and the presence of alternative food increase the coexistence period of intraguild predators.     

Morphology of the first instar of Calliphora vicina, Phormia regina and Lucilia illustris (Diptera, Calliphoridae)

Scanning electron microscopy documentation of first instar Calliphora vicina Robineau-Desvoidy, Phormia regina (Meigen) and Lucilia illustris (Meigen) (Diptera: Calliphoridae) is presented for the first time, and the following morphological structures are documented: pseudocephalon; antenna; maxillary palpus; facial mask; labial lobe; thoracic and abdominal spinulation; spiracular field; posterior spiracles, and anal pad. Light microscopy documentation and illustrations are provided for the cephaloskeleton in lateral and ventral views. New diagnostic features are revealed in the configuration of the facial mask, cephaloskeleton and posterior spiracles. The first instar morphology of C. vicina, Ph. regina and L. illustris is discussed in the light of existing knowledge about early instars of blowflies.