Eristalis

''Eristalis'' is a large genus of hoverflies, family Syrphidae, in the order Diptera. Several species are known as drone flies (or droneflies) because they bear a resemblance to honeybee drones.

Drone flies and their relatives are fairly common generalist pollinators, the larvae of which are aquatic, and breathe through a long, snorkel-like appendage, hence the common name rat-tailed maggots.

''Eristalis'' is a large genus of around 99 species, and is subdivided into several subgenera and species groups (''Eristalomyia'', ''Eristalis'', ''Eoseristalis'' etc.).

Scientific name and grammatical gender

The scientific name was proposed by Pierre André Latreille in 1804. He placed seven species in his new genus, but listed the names as combinations with '' Syrphus'', so it remained unclear what gender he attributed to the name (the gender of the name ''Syrphus'' is masculine). In the two centuries following its publication, ''Eristalis'' was sometimes considered to be of feminine gender, sometimes to be of masculine gender. George Henry Verrall (1901) assigned its gender as masculine, a choice followed in British literature, and also in Dutch, Polish, Czech, Spanish and Portuguese literature. In several other European languages and in North America, the tradition was to consider it as a feminine word. In 1993 the ''International Commission on Zoological Nomenclature'' placed the name on the Official List, and gave its gender as masculine, without justification for that choice. In 2004, Peter Chandler, Andrew Wakeham-Dawson and Angus McCullough submitted an application to confirm the gender of ''Eristalis'' as feminine. They referred to ''ICZN'' Art. 30.1.1, which states that a name in Latin form takes the gender given for that word in standard Latin dictionaries. In ''Composition of Scientific Words'' by R.W. Brown (1954), "eristalis" is listed as a feminine word that refers to an unknown precious stone. The request of Chandler et al. was granted less than two years after submission. As of 2006, ''Eristalis'' is officially a word of feminine gender.

Identification

For terms see Morphology of Diptera.

As a true fly, the species of the genus ''Eristalis'' have a single pair of wings and a pair of halteres. As a member of the family Syrphidae, ''Eristalis'' have a spurious vein in the wing. Defined by Latreille in 1804, ''Eristlis'' was restricted by Meigen in 1882 to those species with a sinuate vein R4+5 and petiolate cell r1.

Since the origin of the genus ''Eristalis'', many genera have been added that refine the description of Latreille such as ''Eristalinus'', ''Meromarcrus, Palpada, Helopilus'' etc. The subtribe Eristalina has been established to contain these genera. Now it is generally accepted as those which have vein R2+3 sinuate, cell r1 usually petiolate and metafemur with basolateral setose patch. With the addition of the following criteria: anepimeron with triangular portion bare, katepimeron pilose, meron bare posteroventrally, without pile anterior or ventral to metathoracic spiracle, eye pilose.

Larvae

The larvae of Eristalini are aquatic and of the long-tailed type. Those of ''Eristalis'' are very commonly found breeding in putrid or stagnant water or in moist excrement, and are called “rat-tailed maggots” or “mousies”.

The "tail" is actually an extendable breathing tube often used to extend above the waterline. This tube allows the larvae to live in oxygen-depleted water such as sewage and stagnant pools where most other larvae cannot exist. Rat tailed larvae also exploit wet mud, manure and moist rotting vegetation. Many species of ''Eristalis'' remain unknown. Working in areas where larvae are likely to be found (e.g. manure pits, sewage seepage and stagnant pools) is difficult and rearing the larvae to adults is even more so. Basic information on many species of ''Eristalis'' remain to be discovered.

Pollination

Adults of ''Eristalis'' species such as the common drone fly (''E. tenax)'' and the orange-legged drone fly (''E. flavipes'') are pollen and nectar feeders with hairy bodies capable of picking up and transferring pollen, and may act as keystone pollinators in some systems. Pollinating ''Eristalis'' species are often generalists, and are known to act as pollinators for common crops such as '' Brassica rapa'', common onion (''Allium cepa''), sweet pepper (''Capsicum annuum''), kiwifruit (''Actinidia deliciosa''), and apples (''Malus domestica''). ''Eristalis'' are tetrachromats, with strong colour differentiation and preferences towards yellow flower colours, compared to trichromatic bees which often prefer blue hues. On islands where bees are absent, their colour preferences may induce selection for higher proportions of yellow in flowers, and they can be seen as frequent and effective pollinators for plants like moon tree foil (''Medicago citrina''). The mobility of hoverflies may aid in long-distance pollen transfer, facilitating gene flow between unconnected plant populations.

Some species, particularly ''E. tenax,'' have been suggested as candidates for a managed pollination alternative to European honey bees (''Apis mellifera'') due to their similar pollination efficacies, abundance, wide distribution, flight range, behavioural plasticity, and high reproductive success. Multiple generations may be reared per year, and ''Eristalis'' are readily reared in laboratory conditions. However, there are challenges concerning commercial mass rearing, retaining numbers, and impacts on non-target species. Due to their ability to fly long distances, dispersal of captive-reared populations may pose a risk to nearby farm equipment and machinery. ''Eristalis'' may also act as mechanical vectors for parasites affecting bees, such as ''Crithidia bombi''.

Interactions with humans

The larvae of ''Eristalis'' species may be considered pests where they affect livestock, contaminating feed and affecting electrical supplies due their mass congregations seeking dry sites for pupation. Some species of ''Eristalis'' have been known as a rare cause of myiasis, with larvae capable of surviving gastric fluids upon ingestion. Symptoms of myiasis from ''Eristalis'' species include diffuse abdominal pain and diarrhoea. Treatment may include anthelmintics such as ivermectin.

Species

Gallery

References

{{Authority control

Eristalini
Hoverfly genera
Taxa named by Pierre André Latreille