Episyrphus Balteatus Research Articles

Landscape parameters explain the distribution and abundance of Episyrphus balteatus (Diptera: Syrphidae)

We studied the importance of forest structure (shape, edge length and orientation) and the crop mosaic (percentage of crops in the total land cover, within 100 and 2000 m from the forests) to the dynamics of an aphidophagous hoverfly Episyrphus balteatus. Adults were collected by Malaise traps located within and on the south- and north-facing edges of 54 forests. In winter, E. balteatus was only found on south-facing edges because of the greater insolation and temperature. In summer, it was more abundant on north-facing edges because of the abundant presence of flowers. In spring, more adults were found on long and south-facing edges than on northern edges. The presence of shrubs within 2000 m also positively affected abundance. In autumn, abundance was positively associated with length of the north-facing edge and forest shape. Emergence traps revealed that in southern France, E. balteatus may overwinter in the larval or puparial stage in forest edges. Overwintering was earlier reported only in adults. Landscape structure, length of forest edges and probably presence of shrub fallows, influence abundance of Episyrphus balteatus.

Role of (E)-β-farnesene in systematic aphid prey location by Episyrphus balteatus larvae (Diptera: Syrphidae)

The foraging behaviour of beneficials such as aphidophagous predators depend largely on volatile compounds emitted by potential preys. Even if polyphagous predatory species are considered, all the potential preys are not systematically localised and accepted. In this work, chemical cues from different aphids and plants, each alone or in association, were studied to elucidate their role in prey location. Using a four-arm olfactometer, attraction of combinations of three aphid (Megoura viciae, Acyrthosiphon pisum and Aphis fabae) and one plant (Vicia faba) species for Episyrphus balteatus larvae was observed. Predatory hoverfly larvae were attracted by all tested stimuli in the presence of aphids, whatever the species. Whole or crushed aphids and also aphids on bean plant parts were attractive to syrphid larvae, but the host plant alone did not present any infochemical role for E. balteatus. Identifi- cation and quantification of the volatile releases from aphid and plant species, alone or in association, were performed using SPME and GC-MS methods. Aphid alarm pheromone, (E)-E-farnesene, was found in the volatile pattern of each aphid and was tested for its role as an effective kairomone for the hoverfly.

Restriction fragment length polymorphisms of different DNA regions as genetic markers in the hoverfly Episyrphus balteatus (Diptera: Syrphidae)

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis using mitochondrial (A+T-rich region; mtDNA) and genomic (zen-region; nDNA) DNA was performed on 182 female individuals of Episyrphus balteatus (DeGeer), a widespread aphidophagous hoverfly with supposed migratory behaviour. Specimens originated from 13 sampling sites in six European countries. The analyses revealed 12 and 18 haplotypes, respectively, for the two DNA types, several of them with a wide distribution, although seven and eight haplotypes, respectively, occurred only in one location. In contrast to other studies on mobile insects, the genetic diversity was relatively high. However, lack of population subdivision, low genetic distances between populations, the very high gene flow rates, and the complete lack of isolation by distance suggest that E. balteatus populations are largely connected and that there is an absence of large-scale geographic structuring. These results support the hypothesis that E. balteatus is a migratory hoverfly species, capable of moving over large distances. These findings related to the seasonal migrations of this species are discussed.

Colonization of apple orchards by predators of Dysaphis plantaginea: sequential arrival, response to prey abundance and consequences for biological control

Episyrphus balteatus (DeGeer) (Diptera: Syrphidae), Adalia bipunctata (L.) (Coleoptera: Coccinellidae) and Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) are the three most abundant natural enemies of Dysaphis plantaginea Passerini (Homoptera: Aphididae) in Asturian (NW Spain) apple orchards. They attack this aphid in sequence: E. balteatus arrived first, followed by A. bipunctata and then by A. aphidimyza. The cecidomyiids arrived too late to have a regulating effect. The syrphids laid an average of 2.3 ± 1.7 eggs per aphid colony and the coccinellids 18.4 ± 9.9 regardless of the degree of the infestation rates of the apple shoots. This value corresponds to the size of an egg batch laid by one female. Therefore, these aphid predators did not respond numerically to the abundance of the pest. The results of this study indicate that natural populations of syrphids and ladybird beetles are unable to control D. plantaginea, and therefore a more complex strategy than waiting for natural enemies is required.

A novel method to investigate the pollen diets of hoverflies

A novel method to investigate the pollen diets of hoverflies is described. The method dispenses with the need for dissection skills or the use of hazardous chemicals thus making it particularly useful for school, college or undergraduate projects and for amateurs. It utilises the properties of the indigestible pollen coat, or exine, which enables pollen to pass through the gut of a hoverfly intact and remain identifiable, even when defaecated. Importantly it does not require the harvesting of insects making it particularly useful for work with rare species. The method was used to investigate the pollen diet of marmalade flies (Episyrphus balteatus) caught in a meadow but it could also be used to investigate many other aspects of syrphid ecology.

Effects of neem‐treated aphids as food/hosts on their predators and parasitoids

Abstract: Experiments were conducted in the laboratory and in greenhouses. Of three neem preparations sprayed upon eggs, only neem oil (NO) exerted a negative impact on the hatching rate of Coccinella septempunctata and Chrysoperla carnea. First instar larvae of Episyrphus balteatus proved to be highly susceptible, when feeding 24 h on aphids sprayed with neem kernel water extract (NKWE). First instar larvae of C. septempunctata showed a very high mortality when feeding on aphids sprayed with different neem preparations. Aphid feeding and live span was reduced. When NKWE had been applied to the soil, the mortality of larvae of E. balteatus and C. septempunctata were lower, when feeding on aphids. Second instar larvae of C. septempunctata were far less susceptible when feeding 48 h on neem‐sprayed aphids than first instars; the time of their development was prolonged, and aphid consumption reduced. Larvae of C. carnea proved to be less susceptible, when feeding on neem‐sprayed aphids, than E. balteatus and C. septempunctata. In C. carnea, however, significant influences were also observed in aphid consumption, time of development, mortality, longevity, and rate of deformity. NO, containing a very low concentration of azadirachtin A, had stronger negative effects than NeemAzal‐T/S®, in all observations. In the parasitoid Diaeretiella rapae, NKWE application to the soil induced negative reactions, when aphids on these plants were parasitized: low percentage parasitization, lowered mummy weight, low emergence rate of adults of F1 and even of F2. Foliar sprays of NKWE had less severe effects in this parasitoid species. The results are discussed with regard to their theoretical and practical significance.

Effects of mass releases of Trichogramma brassicae on predatory insects in maize

AbstractWe investigated whether mass releases of Trichogramma brassicae against the European corn borer will have detrimental effects on populations of other natural enemies in maize. In a tiered approach, experiments investigated the host acceptance of T. brassicae towards eggs of Chrysoperla carnea, Episyrphus balteatus, Adalia bipunctata, and Coccinella septempunctata under laboratory, caged, and field conditions. The factitious host, Ephestia kuehniella, and in one case also Mamestra brassicae were used as control. Under laboratory conditions, 53% of the T. brassicae females parasitised C. carnea eggs, 70% parasitised E. balteatus eggs, while 91% of the females parasitised E. kuehniella eggs, with T. brassicae emerging from C. carnea, E. balteatus, and E. kuehniella at rates higher than 81%. No parasitoid offspring emerged from eggs of A. bipunctata and C. septempunctata. However, we observed significantly increased mortality on A. bipunctata eggs, compared to the control, and also found young instars of T. brassicae inside A. bipunctata eggs. In a second experiment where the host acceptance behaviour of the parasitoid female was directly observed for 10 min, 10% of T. brassicae females were found to oviposit in eggs of A. bipunctata, but the development of parasitoid offspring failed. No C. septempunctata eggs, 13% of E. balteatus eggs, 23% of C. carnea eggs, 33% of E. kuehniella egg clusters, and 83% of M. brassicae eggs were accepted for oviposition. In the greenhouse under caged conditions, the parasitism rate of C. carnea eggs (7%) and E. balteatus eggs (0.4%) were significantly lower than of E. kuehniella eggs (21 and 27%, respectively). In the final tier, 3.1% of C. carnea eggs were parasitised by T. brassicae under field conditions. This was significantly less than the observed parasitism rate of E. kuehniella egg clusters (64%). From direct observations of the parasitoids’ host acceptance behaviour and the low parasitism rates observed under caged and field conditions, we conclude that detrimental effects of the mass release of T. brassicae on populations of natural enemies in maize are unlikely to occur.

The interplay between density- and trait-mediated effects in predator-prey interactions: a case study in aphid wing polymorphism.

Natural enemies not only influence prey density but they can also cause the modification of traits in their victims. While such non-lethal effects can be very important for the dynamic and structure of prey populations, little is known about their interaction with the density-mediated effects of natural enemies. We investigated the relationship between predation rate, prey density and trait modification in two aphid-aphid predator interactions. Pea aphids (Acyrthosiphon pisum, Harris) have been shown to produce winged dispersal morphs in response to the presence of ladybirds or parasitoid natural enemies. This trait modification influences the ability of aphids to disperse and to colonise new habitats, and hence has a bearing on the population dynamics of the prey. In two experiments we examined wing induction in pea aphids as a function of the rate of predation when hoverfly larvae (Episyrphus balteatus) and lacewing larvae (Chrysoperla carnea) were allowed to forage in pea aphid colonies. Both hoverfly and lacewing larvae caused a significant increase in the percentage of winged morphs among offspring compared to control treatments, emphasising that wing induction in the presence of natural enemies is a general response in pea aphids. The percentage of winged offspring was, however, dependent on the rate of predation, with a small effect of predation on aphid wing induction at very high and very low predation rates, and a strong response of aphids at medium predation rates. Aphid wing induction was influenced by the interplay between predation rate and the resultant prey density. Our results suggests that density-mediated and trait-mediated effects of natural enemies are closely connected to each other and jointly determine the effect of natural enemies on prey population dynamics.

Influence of prey host plant on a generalist aphidophagous predator: Episyrphus balteatus (Diptera: Syrphidae)

Secondary plant metabolites (allelochemicals) play a major role in plant-insect interactions. Glucosinolates (GLS) and their degradation products from Brassica species are attractants and feeding stimulants for Brassicaceae specialist insects but are generally repellent and toxic for generalist herbivores. The impact of these compounds on crucifer specialist insects are well known but their effect on generalist predators is still not well documented. The influence of the prey's host plant on both development and reproduction of an aphidophagous beneficial, the hoverfly Episyrphus balteatus, was determined using the cabbage aphid, Brevicoryne brassicae (a specialist) and the peach aphid Myzus persicae (a generalist) reared on two crucifer plants, Brassica napus and Sinapis alba containing low and high GLS levels respectively.The prey and its host plant differently influenced life history parameters of E. balteatus. The predator's rates of development and survival did not vary when it fed on the generalist aphid reared on different host plants. These rates decreased, however, when the predator fed on the specialist aphid reared on the host plant with high GLS content plant versus the host plant with lower GLS content. This aphid host plant combination also negatively affected hoverfly reproduction; lower fecundity was observed. As a result, the fitness of the hoverfly was strongly affected. This study illustrates the importance of tritrophic relations in pest management involving predators. The host plant of the prey can have a major influence on the potential of a biological agent to control herbivore species such as aphids.

Intraguild predation on the aphid parasitoid Lysiphlebus fabarum (Marshall) (Hymenoptera: Aphidiidae): mortality risks and behavioral decisions made under the threats of predation

Abstract Intraguild predation (IGP) is a primordial mortality factor that generates consequences for the coexistence of species in natural communities as well as for the implementation of antagonists in biological control programs. Among parasitoids and predators the most frequent form of IGP is asymmetric. Because it exerts a strong selection pressure on the inferior parasitoids it seems to be likely that these antagonists have evolved strategies to minimize IGP. Our study traced the behavior of the aphid parasitoid Lysiphlebus fabarum (Marshall) which is able to exploit the enemy free space in ant protected aphid colonies. In the agricultural landscape, L. fabarum frequently forages in aphid colonies without ant protection where it is exposed to situations with an extraordinary high risk of predation by aphidophagous predators. In the current study, we investigated predation risks for different developmental stages of L. fabarum and behavioral decisions made under the risk of predation by foraging females. All developmental stages of L. fabarum suffered from a high risk of predation in confrontations with most of the tested aphidophagous predators. Only aphid mummies turned out to be a less frequent IG-prey compared to unparasitized aphids when found simultaneously with adult Coccinella septempunctata L. and larvae of Episyrphus balteatus de Geer. Nevertheless, foraging females of L. fabarum did not avoid the presence of predators nor displayed an effective defense behavior in direct confrontations with any of the tested predator species. Coccinellids, syrphids as well as chrysopids proved capable of killing an adult parasitoid. The discrepancies between the observed predation risks and the lack of behavioral adaptations of adult L. fabarum are discussed in different contexts.

Hoverfly Glutathione S-Transferases and Effect of Brassicaceae Secondary Metabolites

The Episyrphus balteatus hoverfly is commonly found in very diversified biotopes including Brassicaceae crop fields. Glutathione S -transferases (GST) are detoxification enzymes that are involved in the metabolization of plant allelochemicals such as glucosinolates and related volatile products (mainly isothiocyanates) from Brassica plants. Developmental expression of E. balteatus glutathione S -transferases was studied. With regard to the high level of glutathione S -transferase activity in syrphid adults, the latter stage was also used to assess the glutathione S -transferase distribution in several parts of the insect. Higher glutathione S -transferase activities were found in the thorax (47.5 and 38.5%) followed by the abdomen (32.4 and 32.9%) and the head (20.4 and 28.5%) with 1-chloro-2,4-dinitrobenzene, and 2,4-dinitro-l-iodebenzene, respectively. Analysis of Brevicoryne brassicae , the cabbage aphid, by GC-MS revealed the presence of isothiocyanates. The latter are the main degradation products of the glucosinolate from the host plant at neutral pH. Feeding the predators with this aphid species and with the generalist Myzus persicae reared on Brassica napus induced glutathione S -transferase activity. Impact of volatiles from the host plant on the glutathione S -transferase activity was also determined by exposure of syrphid larvae to isothiocyanates (allyl- and benzyl-isothiocyanates). Enzyme inductions were observed only from a 1 ppm concentration. Enzymatic activity evolution was discussed as an adaptation to cope with allelochemicals from plants. Finally, the glutathione S -transferase activities of several hoverfly species were compared in relation to their feeding behavior (coprophagous, saprophagous, and aphidophagous) at the larval stages. The results seem to indicate quantitative and qualitative differences of glutathione S -transferases according to the feeding behavior of the larvae.

Oviposition behaviour and host colony size discrimination in Episyrphus balteatus (Diptera: Syrphidae)

Three bioassays were used to examine the oviposition behaviour of the hoverfly, Episyrphus balteatus (Degeer) in which various stimuli purported to influence host assessment and choice were tested. Episyrphus balteatus failed to exhibit enhanced behavioural responses, in terms of approaches and landings, to artificial leaves with the highest numbers of aphids, suggesting that females are merely responding to the colour of the artificial leaves. A density-dependent oviposition response was reported in a second bioassay using whole bean plants, although there was an asymptotic relationship. Syrphid responses, which were measured by oviposition over a five-day period, were greatest towards those plants with the highest number of aphids. In a final series of trials, gravid female E. balteatus showed a behavioural preference for filter papers treated with the greatest honeydew concentrations (0.26 mg microl(-1) honeydew). More time was spent in the treated areas and syrphids demonstrated more proboscis and ovipositor extensions in these treatments. These bioassays provided an opportunity to isolate some of the individual components of decision-making by female E. balteatus during egg-laying behaviour. A greater understanding of natural enemy behaviour is essential before enhanced control of pest populations in the field can be established.

Scale effects on the attachment pads and friction forces in syrphid flies (Diptera, Syrphidae).

To test the role of constructional and dimensional factors in the generation of friction force by systems of setose attachment pads, six species of syrphid fly (Platycheirus angustatus, Sphaerophoria scripta, Episyrphus balteatus, Eristalis tenax, Myathropa florea and Volucella pellucens) were studied using light and scanning electron microscopy. Flies were selected according to their various body mass and attachment pad dimensions. Such variables as pad area, setal density, the area of a single setal tip and body mass were individually measured. A centrifugal force tester, equipped with a fibre-optic sensor, was used to measure the friction forces of the pads on a smooth horizontal surface made of polyvinylchloride. Friction force, which is the resistance force of the insect mass against the sum of centrifugal and tangential forces, was greater in heavier insects such as Er. tenax, M. florea and V. pellucens. Although lighter species generated lower frictional forces, the acceleration required to detach an insect was greater in smaller species. The area of attachment pads, setal tip area and setal density differed significantly in the species studied, and the dependence of these variables on body mass was significant. The frictional properties of the material of the setal tips were not dependent on the dimensions of the fly species. Similar results were obtained for the frictional properties of the pulvillus as a whole. Thus, the properties of the secretion and the mechanical properties of the material of the setal tips are approximately constant among the species studied. It is concluded that differences in friction force must be related mainly to variations in the real contact area generated by the pad on the smooth surface. The real contact area can be estimated as the summed area of the broadened setal tips of the pad in contact with the surface. The real contact area depends on such morphological variables as setal density and the area of a single setal tip. Although individual variables vary among flies with different dimensions, they usually compensate such that smaller setal tip area is partially compensated for by higher setal density.

Intraguild Predation among the Hoverfly Episyrphus balteatus de Geer (Diptera: Syrphidae) and Other Aphidophagous Predators

Abstract Aphidophagous predators compete for the same prey species. During their foraging activity they frequently encounter heterospecific aphid predators. These situations can lead to intraguild predation and may disrupt biological control efforts against aphids where more than one predator species is present. We investigated the behavior of larvae of the hoverfly Episyrphus balteatus de Geer and its interaction with three other aphid predators: the ladybird Coccinella septempunctata L., the lacewing Chrysoperla carnea Stephens, and the gall midge Aphidoletes aphidimyza (Rondani). Interspecific interactions between predators were examined in arenas of different sizes and in the presence of extraguild prey. The outcome of interactions between E. balteatus larvae and the other predators depended predominantly on the relative body size of the competitors. Relatively large individuals acted as intraguild predators, while relatively smaller individuals became intraguild prey. Eggs and first- as well as second-instar larvae of E. balteatus were highly susceptible to predation by all other predators, whereas pupae of E. balteatus were preyed upon only by the larvae of C. carnea. Interactions between A. aphidimyza and E. balteatus were asymmetric and always favored the latter. Eggs and first- as well as second-instar larvae of E. balteatus sustained intraguild predation irrespective of the size of the arena or the presence of extraguild prey. However, the frequency of predation on third-instar larvae of E. balteatus was significantly reduced. This study indicated that the same species can be both intraguild predator and intraguild prey. It is suggested that combinations of predators must be carefully chosen for success in biological control of aphids.

Distribution and abundance of aphidophagous hoverflies (Diptera: Syrphidae) in wildflower patches and field margin habitats

Summary1 The spatial and temporal variations in aphidophagous syrphid abundance were recorded over two seasons in wildflower resource patches sown in a winter barley crop and associated field margins. Standard census techniques and sticky board trapping were used to assess numbers of syrphids, whilst weekly flower head counts were used to quantify the floral resources available in each of the patches.2 The field margin supported a greater diversity and density of syrphids than the within‐crop wildflower patches, despite having a relatively lower flower head density. Presumably this was in response to other resources that field margins offer, namely additional aphid resources, shelter from predation, lekking sites and suitable flight‐paths.3 The commonest species of syrphid, Episyrphus balteatus, demonstrated a very positive habitat association with the field margin and was rarely reported in the field patches. Therefore, it may be an unsuitable candidate for the biological control of aphids via augmentation of numbers using non‐host resources.4 Patch size and shape had little effect on the spatial distributions of syrphids, probably because of the adult syrphids' high mobility.5 Of greater influence was the number of flowers contained in each habitat patch. Typically, patches with higher numbers of flowers had significantly greater aggregations of hoverflies. Habitat manipulation by the provision of flowers in patches seems to increase the local density of hoverflies. Further work is necessary to establish the importance of flower density in enhancing the control of pest populations.

Effect of hunger on yellow water trap catches of hoverfly (Diptera: Syrphidae) adults

Summary1 An experiment was conducted in a winter wheat field using yellow water traps at crop height and at ground level, near to and distant from flowers, to test the hypothesis that such traps are seen as a source of food by flower‐feeding adult hoverflies and are therefore likely to selectively trap hungry individuals. Hoverflies caught in each trap were counted and identified and the amount of pollen in their guts was assessed. Ratios of numbers of hoverflies seen in the wheat crop to numbers caught in nearby traps were compared for the different treatments.2 Most hoverflies were caught in crop‐high traps but they included a high proportion of individuals with empty guts. The taxa were: Episyrphus balteatus (De Geer), Metasyrphus corollae (F.) (these species together accounted for over 90% of the individuals trapped), with Sphaerophoria spp., Syrphus spp., Scaeva pyrastri (L.), Melanostomini and unidentified others making up the rest.3 Significantly fewer hoverflies were captured in low than in high traps. The ratios of numbers trapped to numbers observed, in flower and in no flower treatments would be expected to be the same if the traps were not selective. This was supported for low traps. With high traps, however, there was a highly significant difference between the ratios (71.34 and 126 : 8, respectively).4 Flies captured in high traps had less pollen in their gut than those captured in low ones. At each distance, more E. balteatus captured in high traps were in pollen category 1 (< 20 grains) than in any other category. The opposite state was seen in low trap catches, where most flies were in category 5 (> 5000 grains). Median pollen categories were 2 (21–200 grains) and 4 (1501–5000 grains) for flies caught in high and low traps, respectively.5 The ecological selectivity of traps according to their height and the physiological condition of the targeted individuals is a problem likely to affect many trapping systems apart from the one described in this paper.

Selectivity in the exploitation of floral resources by hoverflies (Diptera: Syrphinae)

Adults of the Syrphinae subfamily display no strong flower preferences but exploit pollen and nectar produced by native plants having large inflorescences and flat corollae (e.g. Apiaceae, Asteraceae. Ranunculaceae and Rosaceae). Seven foraging guilds are defined according to the dietary patterns of hoverflies, reflecting mainly a sequential exploitation of flowers at different times of the year and in different habitats.The majority of species live in forests where they form highly diversified communities. Few Syrphinae colonize successfully open and anthropogenic habitats, such as field margins and fallow areas.Episyrphus balteatus, Melanostoma mellinum, Eupeodes corollae, Sphaerophoria scriptaandPlatycheirusspp. are dominant in the communities of Syrphinae from open habitats, all over western Europe. These species are highly polyphagous and characterized by elongated mouthparts as well as a long and slender body. They have access to pollen and nectar in flowers with small and tubular corollae. It is suggested that their polyphagy is an important asset for colonizing open and ephemeral habitats.

The phenology of Syrphidae (Diptera): are they Batesian mimics of Hymenoptera?

The phenology of aculeate Hymenoptera and of syrphids which are believed to mimic them has been investigated at three semi-natural ancient woodland sites in north-west England. It is concluded that the abundance and phenology of most of the hoverflies is consistent with their being Batesian mimics of particular species of bee or wasp. The main exceptions are Eristalis spp., Helophilus spp Syrphus spp. and Episyrphus balteatus which are often much more abundant than their supposed models. These four taxa may still benefit from mimicry, but further research is needed to confirm this. With the possible exceptions of Eristalis pertinax and E. tenax, there is no strong evidence from north-west England in support of Waldbauer's hypothesis that mimics are rare when fledgling birds are abundant but may be commoner in autumn and spring. The data also indicate that mimics which closely resemble their models (specific mimics) are usually rarer than their models, whereas mimics with a less precise resemblance (non-specific mimics) are often commoner than models.

The phenology of Syrphidae (Diptera): are they Batesian mimics of Hymenoptera?

The phenology of aculeate Hymenoptera and of syrphids which are believed to mimic them has been investigated at three semi-natural ancient woodland sites in north-west England. It is concluded that the abundance and phenology of most of the hoverflies is consistent with their being Batesian mimics of particular species of bee or wasp. The main exceptions are Eristalis spp., Helophilus spp., Syrphus spp. and Episyrphus balteatus which are often much more abundant than their supposed models. These four taxa may still benefit from mimicry, but further research is needed to confirm this. With the possible exceptions of Eristalis pertinax and E. tenax, there is no strong evidence from north-west England in support of Waldbauer's hypothesis that mimics are rare when fledgling birds are abundant but may be commoner in autumn and spring. The data also indicate that mimics which closely resemble their models (specific mimics) are usually rarer than their models, whereas mimics with a less precise resemblance (non-specific mimics) are often commoner than models.

Development of ovaries, allometry of reproductive traits and fecundity of Episyrphus balteatus (Diptera: Syrphidae)

Episyrphus balteatus only matures eggs after emergence. Ovaries develop in 4 stages. In the absence of oviposition sites, females refrain from ovipositing and their ovaries progressively fill the abdomen and then egg resorption occurs. The potential fecundity, which is expressed by the ovariole number, the reproductive biomass and the abdomen volume, scales isometrically with the size of females. Egg size is much less variable and does not rise proportionally to body size. In laboratory conditions, females of E. balteatus might lay between 2,000 and 4,500 eggs during their life-time at a rate of 1 to 2 eggs per ovariole per day. Both life-time fecundity and rate of egg production are directly related to the size of females. The potential and realized fecundities are likely to be limited by the availability of food resources during larval and adult life, respectively.