New data on the distribution and biology of the invasive species Hydrotaea aenescens ( Wiedemann , 1830 ) ( Diptera , Muscidae )

Introduced from the New World, H. aenescens has spread rapidly in Europe. Th is paper reports new records of H. aenescens from Eastern Europe. Among these records, the one from the far north of European Russia is the most remarkable. New data on the seasonal activity and mating behaviour of H. aenescens are also given. A peak of H. aenescens imago activity in southern Turkey takes place during very early spring. Th e mating behaviour of H. aenescens diff ers from that of other members of the genus Hydrotaea.


Introduction
Hydrotaea aenescens is widely distributed in the Neotropical and Nearctic regions, and was introduced into Europe around 1960 (Saccà 1964).Current data on the dispersal of H. aenescens in Europe is given in Pont et al. (2007).
From my experience, the most attractive substrate for H. aenescens is vertebrate carrion.On the same substrate, I usually found H. aenescens together with another Hydrotaea -our common indigenous H. ignava (Harris).Both fl ies look alike due to their unmodifi ed fore femur and strong metallic shine (previously they were placed in the genus Ophyra), and they have obvious synanthropic trends.When caught, H. aenescens is unmistakable due to its yellow palpi.In the fi eld H. aenescens is slightly smaller and has a greenish shine instead of the bluish shine in H. ignava.I decided that it would be interesting to compare the behaviour, and especially the courtship and mating strategies, of these two species.

Material and methods
To attract H. aenescens, I used vertebrate carcasses (dog, cat) found near roads.Th ese animals had been killed in road accidents and were in various stages of decomposition.Usually I had to move the carcass away from the road to a more suitable place where neither the fl ies nor I would be disturbed.
Observations took place in Turkey near Antalya and in Russia near Sochi and near Narjan-Mar (Fig. 1), between September 2007 and July 2008.
Th e collected material is stored in the Zoological Museum of Moscow State University, Russia.
To understand the mating behaviour, I simply used visual observations, and I recorded what I saw using photography (CanonD20 digital camera with Canon 100mm/2.8macro lens).
Th e only female of H. aenescens was collected among 15-20 females of H. ignava.No males recorded.
Turkey, Antalya, near Side, sand dune with pine trees, 21-27 February 2008, dog carcass.H. aenescens was numerous, with a male/female ratio 2 : 1. H. ignava was not recorded at all.Turkey, Antalya, near Side, Lake Titreyen, 21-27 February 2008, another dog carcass, half-buried under sand.H. aenescens was common, with a male/female ratio 2 : 1. H. ignava was not recorded at all.Turkey, Antalya, near Side, Lake Titreyen, 30-31 March 2008, the same dog carcass, half-buried under sand.H. aenescens was less common than one month previously, with a male/female ratio about 1 : 1. H. ignava, on the contrary, appeared in great numbers, with more males than females.Males of H. ignava hovered above carrion at a height of 10-50 cm.
Russia, Nenetsk Nat.Res., 60 km north of Narjan-Mar, 68.15N 53.65E, 9-11 July 2008.Males and females of H. aenescens were found in and around a refuse pit for rotten fi sh waste and kitchen garbage.Th is refuse pit was near a fi shing shack used by fi shermen and scientists.Th e hut was situated at least 50 km away from the nearest inhabited village.
Phenology.It might be thought that H.aenescens, being originally a Neotropical species, might be a warmth-loving species.On the contrary, however, in South Turkey it is among the very few Diptera that emerge as early as in February.Th e high percentage of males and high courtship-mating activity observed in February testify to the fact that these were not overwintering fl ies but rather a freshly emerged generation.
When it comes to comparing diff erent fi eld observations, there must always be some doubt as to whether the situations are strictly comparable -an observer may suppose the sites and the substrates to be approximately the same, but the fl ies may not see things in the same way.Th e dog carcass discovered near Lake Titreyen was placed so as to rule out such a possibility.Because it was half-buried under the sand, decomposition was defi nitely proceeding more slowly than usual and the carcass remained attractive to carrion visitors for a long time.Observations of this carcass showed that H. aenescens appeared one month earlier than H. ignava.We could also observe that in hot periods H. aenescens became much less common than H. ignava.
Th e larvae of H. aenescens are often regarded as potential antagonists of the larvae of Musca domestica Linnaeus (Skidmore 1985).I doubt that such antagonism takes place, at least in Southern Turkey.Th e activity of M. domestica occurs chiefl y in the hot season, and H. ignava seems much more suited to be a M. domestica antagonist than H. aenescens.
Distribution.Russia is a new record for H. aenescens.In the map (Fig. 1), the countries from which H. aenescens has been recorded (Pont et al. 2007) are marked in green.Th e map shows that the report of H. aenescens from the southern part of European Russia was rather predictable.However, the record from the Pechora River delta was unexpected.It is interesting that the most northern previously known locality for H. aenescens was southern Norway (Rognes 1982), but there are signifi cant diff erences between the more gentle Atlantic climate of Norway and the extremely severe conditions of the Russian polar tundra.Under these conditions, most of the temperate Diptera fauna is replaced by a boreal fauna.Th e coldresistance of H. aenescens discussed above is likely to account for its occurrence in a boreal region.Another consideration is the distinct synanthropic trend in H. aenescens.My indoor collection of several specimens of H. aenescens in February-March in Turkey supports this possibility, as I have never collected other members of the genus Hydrotaea indoors.

II. Mating
Mating behaviour was observed on the dog carcasses during the period 22-27 February 2008.Males were found sitting on and around carrion, often changing positions but clearly avoiding shaded sites.I would characterize the mating behaviour of H. aenescens as follows: trying to copulate with any fl y of the same size or bigger (preferred), with a metallic shine, in sunlight.Females spent more time in the shade under the carcass, where it was suitable for oviposition, and were not commonly the object of such courtship, but male-to-male mating attempts were regular and numerous.Th is behaviour was diffi cult to record on camera since the male underneath immediately tried to escape or to change his position to the upper one.To make an image of an immobile copulating pair attacked by another male was a much easier task.
Calliphoridae of both sexes also attract H. aenescens males.Fig. 3 shows Lucilia sericata (Meigen) (large and shining, as H. aenescens prefers) and Calliphora vomitoria (Linnaeus) (not very shining, but large in size) with H. aenescens males.However, the species that suff ers the most from this sexual harassment is Chrysomya albiceps (Wiedemann).Th is can be described as a case of 'the biter being bitten himself ', because, in their turn, males of C. albiceps display the same mating behaviour with male-to-male attempts and the disturbance of copulating pairs by another male(s).Th e next photograph will illustrate this (Fig. 4).
Piophilidae, Sarcophagidae and Fanniidae were totally ignored, probably because they were too small or not shining.
A normal copulation of H. aenescens was also observed, although not very often.Copulation was on or around carrion and lasted for 2-6 minutes.
In late March, males of H. ignava exhibited a very spectacular hovering behaviour above carrion.
No hovering/swarming by H. aenescens was observed during my observations.Furthermore, I am certain that it never happens because swarming is replaced by the mating behaviour described above.To my knowledge, the non-swarming courtship of H. aenescens is unique in the genus Hydrotaea.