Aphidophagous Hoverflies Research Articles

Relative Attractiveness of Potential Beneficial Insectary Plants to Aphidophagous Hoverflies (Diptera: Syrphidae)

Establishing flowering plants in and around fields to provide pollen and nectar resources for natural enemies has shown promise as a strategy to enhance biological control of crop pests. Natural enemies are selective in their flower feeding, however, and show preferences for certain plant species. In this study the relative attractiveness of 11 flowering plant species to aphidophagous hoverflies (Diptera: Syrphidae) was evaluated at the Oregon State University Vegetable Research Farm. Six of these plant species were also evaluated at two other farm sites. Of the 12 species of hoverflies collected, Meliscaeva cinctella (Zetterstedt), Toxomerus marginatus (Say), Toxomerus occidentalis (Curran), Sphaerophoria sulfuripes (Thomson), and Scaeva pyrastri (L.) were common to all three sites. Attractiveness of flowering plants to foraging hoverflies was assessed by conducting timed observations of feeding-visit frequencies. Flowering periods varied between plant species and comparisons were made only for plant species flowering on a particular date. Relative attractiveness of plant species to hoverflies differed between dates and sites. Among early-season flowering species, coriander, Coriandrum sativum (L.), was fed from most frequently. Among late-season flowers, yarrow, Achillea millefolium (L.), fennel, Foeniculum vulgare (Miller), and Korean licorice mint, Agastache rugosa (Fischer & C. A. Meyer) were fed from most frequently. These results help in the selection of plants to enhance biological control, but final selection of plants for this purpose requires considering flower, natural enemy, and pest phenologies, and pollen and nectar quality and availability.

The effect of egg load and host deprivation on oviposition behaviour in aphidophagous hoverflies

Summary1. Two species of aphidophagous hoverfly, Episyrphus balteatus and Syrphus ribesii, were tested for the effects of egg load and host deprivation on oviposition choices.2. Egg load affected the total number of eggs laid in E. balteatus but not in S. ribesii, however it did not affect the proportion laid on any one aphid in E. balteatus but did affect the proportion laid on any one aphid in S. ribesii. The rank order of preferences remained unchanged by age or host deprivation.3. The dominant effects on host choices were aphid species (in both syrphids) and presentation order (in E. balteatus).4. Being deprived of hosts increased egg load substantially in E. balteatus, and increasing time of deprivation also had an effect on discrimination; there was no effect of host deprivation in S. ribesii.5. Reasons for these patterns are discussed.

The influence of floral character on the foraging behaviour of the hoverfly, Episyrphus balteatus

AbstractA bioassay to examine the foraging behaviour of the aphidophagous hoverfly, Episyrphus balteatus was used in which various stimuli purported to influence flower choice were tested using model flowers. In choice experiments, E. balteatus exhibited enhanced behavioural responses to the colour yellow, as previously seen in Eristalis by several workers. Previous suggestions that the generalist forager E. balteatus has no preference for colour are re‐examined in the light of this new evidence. The other advertisement cue tested, size, was also demonstrated to play an important role in determining foraging behaviour, with the smaller artificial flowers seemingly preferred. Of the rewards tested, E. balteatus showed preference for the greatest nectar concentrations, whilst increasing pollen did not affect behaviour. These bioassays provided an opportunity to isolate the individual components of decision‐making by E. balteatus during foraging. The separation of sexes and ages in these experiments permitted analysis of inter‐sexual and inter‐generation differences in behaviour, a factor apparently not investigated in previous work.

Density of adult hoverflies (Dipt., Syrphidae) in sown weed strips and adjacent fields

In 1992 and 1993, studies examined numbers of adult hoverflies in sown weed strips, adjacent fields and a field boundary in the Swiss plateau, near Bern. Hoverflies were observed quantitatively and were divided according to their larval food. In both years, distinctly more aphidophagous and aquatic hoverflies were observed in the weed strips than in the adjacent fields. Copro‐ and phytophagous hoverflies were observed in very low numbers and they were almost entirely confined to the weed strips and the field boundary. The weed strips contained a high density of flowering plants and therefore proved to be very attractive feeding places for all hoverflies. Numbers of aphidophagous hoverflies declined slightly with increasing distance from the weed strips. Possible impacts of weed strips in encouraging aphidophagous hoverflies and their potential as aphid antagonists are discussed.

The influence of sown herb strips and spontaneous weeds on the larval stages of aphidophagous hoverflies (Dipt., Syrphidae)

Abstract: The influence of sown herb strips on larval stages of aphidophagous syrphids was studied in different strips and adjacent winter wheat fields near Berne (Switzerland) from 1993 to 1995. The aim of this study was to learn whether these sown herb strips offer a supply of aphids sufficient enough to sustain the first generation of syrphids in spring or a further generation after crop harvest. Aphid infestation of the strips occurred at about the same time as in winter wheat, between the end of May and the beginning of August. A first syrphid generation in spring can therefore not develop on weeds in strips. Furthermore, after harvest no further generations will appear in strips. The highest numbers of syrphid pre‐imaginal stages in 1993 and 1994 were found on spontaneously growing weeds (Rumex obtusifolius, Cirsium arvense and C. vulgare). Among the sown species, Centaurea jacea and Pastinaca saliva showed the highest syrphid larvae densities. The densities in herb strips (max. 0.6 larvae/m2) were manyfold lower than in wheat (10 pupae/nr). In herb strips the same syrphid species as in winter wheat were identified. In both habitats Episyrphus balteatus was the most abundant species. Epistrophe spp. were only found in strips. No dependence of oviposition within wheat fields on the distance to the strips could be demonstrated. Due to their great mobility, it is easy for adult syrphids to find aphid colonies within a crop field. The strips are neither significant for an early development of the first syrphid generation nor for an additional generation after wheat harvest. The importance of herb strips for hoverflies lies in their quality to supply them with pollen and nectar, which increases the fitness of the adults.

Food utilization of aphidophagous hoverfly larvae (Diptera: Syrphidae, Chamaemyiidae) on herbaceous plants in an urban habitat

AbstractWe examined food utilization in a community of aphidophagous hoverfly larvae (Diptera: Syrphidae and Chamaemyiidae) in open lands in an urban habitat in central Japan for 3 years. The community consisted of 17 hoverfly species feeding on 20 aphid species occurring on 14 species of dominant herbaceous plants. In terms of larval prey preference, the dominant eight species of hoverfly were categorized into three groups: a polyphagous ‘generalist’ group consisting of four species, Episyrphus balteatus, Betasyrphus serarius, Syrphus vitripennis and Sphaerophoria sp.; an oligophagous ‘specialist’ group consisting of three species, Metasyrphus hakiensis, Dideoides latus and Paragus hemorrhous; and Leucopis puncticornis, which showed a preference for two aphid species on the plant Torilis scabra. The prey aphids of the second group have behavioral or morphological defense mechanisms that are effective for preventing attacks by generalist hoverflies; two prey aphids are aggressive toward generalist predators and the others are protected by ant‐attendance. The specialist hoverflies seem to be adapted to overcome these defense mechanisms. The prey ranges overlapped little between the generalist and the specialist groups, while those within the generalist group overlapped greatly.

Fitness of the hover flies Episyrphus balteatus and Eupeodes corollae faced with limited larval prey

AbstractDifferences in adult oviposition behavior of the aphidophagous hover flies Episyrphus balteatus (De Geer) and Eupeodes corollae (F.) (Diptera: Syrphidae) led us to formulate and test hypotheses concerning their larval behaviour. In laboratory experiments, larval E. balteatus lived longer when starved than larval E. corollae, and this difference increased with age at which starvation commenced. Larval E. balteatus crawled faster than larval E. corollae, and this difference increased under starvation. Limited aphid supply reduced larval and pupal survival more for E. corollae than for E. balteatus. However, the effect of limited aphid supply on adult body size did not differ for the two species. E. balteatus oviposition and larval behavior make it a more promising candidate for introducing to control Diuraphis noxia (Mordwilko) (Homoptera: Aphididae) where this aphid has become an exotic pest.

Effect of hunger on the allocation of time among pea plants by the larvae of an aphidophagous hover fly,Eupeodes corollae [Dipt: Syrphidae

We observed the movement of predatory larvae of the syrphid flyEupeodes corollae (F.) (formerlyMetasyrphus corollae) among small pea plants with and without aphids. Starved larvae spent longer time than well-fed larvae on similar plants and both groups of larvae stayed longer on plants with aphids than on plants without aphids. On plants with aphids, larvae which failed to capture prey left the plant sooner than those which captured aphids. The capture of at least one aphid on a plant increased the persistence of syrphid larvae. The average rate of energy gain was higher for well-fed larvae than for starved larvae because starved larvac stayed on plants even when their rate of return was lower. When larvae that had captured aphids left plants, their rate of energy gain, tended to be lower than at any time following capture of the 2nd, aphid. The 1st aphid was captured in less time than similar larvae spent on plants without aphids. Time between captures of aphids by well-fed larvae was less than the time such larvae spent on plants without aphids. Among starved larvae, the intercatch intervals were similar to the time on plants without aphids. We discuss the significance of these results relative to current predator foraging theory and the efficiency ofE. corollae as a biological control agent.

THE POLLINATION ECOLOGY OF EPIPACTIS CONSIMILIS DON (ORCHIDACEAE) IN ISRAEL

SummaryObservations on the pollination ecology of Epipactis consimilis Don (Orchidaceae) in Israel are described. The pollinators were found to be eight species of five genera of hover files (Syrphidae), especially Sphaerophoria scripta and S. rueppellii.Different behaviour patterns of the insect species and the sexes thereof are given and discussed. It is suggested that the flower mimics the shape and colour of aphids and this attracts aphidophagous hover flies.