Invasive alien species in Switzerland - Schweizer ...

4 > Insects – Insecta 79
4.5 Diptera
Checklists of Swiss Diptera have been published recently (Merz et al., 1998, 2001).
These do not contain information on the exotic or invasive status of the species but the
authors (Drs. B. Merz, J.-P. Haenni and G. Baechli) were contacted and kindly reviewed
the list to extract the species which are thought to be exotic.
Less than 20 dipteran species in Switzerland are of alien origin. Some are agricultural
or horticultural pests. The Nearctic agromyzids Liriomyza huidobrensis and L. trifolii
are pests of vegetables, mainly in greenhouses but occasionally found outdoors. Another
agromyzid fly, Napomyza gymnostoma, was recently found in Switzerland (Eder
and Bauer, 2003). N. gymnostoma, previously known as a harmless insect from some
European countries, but not Switzerland, mysteriously became a serious pest of onions
and leeks one or two decades ago in several Central and western European countries.
Its origin is not known, although it may be a virulent ecotype of a European species
that unexpectedly adapted itself to agricultural systems and crops. Its sudden pest status
and spread may also be due to changes in pest control methods in leek and onion crops,
or to global warming.
Two of the world’s most serious fruit flies (Tephritidae), the olive fly Bactrocera oleae
and the Mediterranean fruit fly, Ceratitis capitata, both originating from the Mediterranean
region, are also established in Switzerland, where they have reached their
climatic limit and, thus, cause little damage. Two North American tephritids have
recently invaded the country. Rhagoletis completa feeds on walnut and is considered a
pest in its native region. It was discovered in the Ticino in 1991 (Merz, 1991) and,
since then, has spread rapidly to many regions north of the Alps (see Fact Sheet).
Populations are increasing and severe damage has been observed in Switzerland and
Italy. Another American species, R. cingulata, was found at the same time, in cherries
(Merz, 1991, as R. indifferens). Until now, populations have remained very low and it
does not seem to spread as quickly as R. completa.
The North American Drosophilidae Chymomyza amoena attacks various fruits of
broadleaved trees, such as apple, walnut, plum, acorn, etc. It is present in high numbers
in both urban and forest environments. Its spread and ecology in Switzerland have been
studied in detail (e.g. Burla and Baechli, 1992; Band, 1995; Band et al., 1998, 1999).
Another drosophilid, Drosophila curvispina, originating from east Asia, is present in
the Ticino, Vaud and Valais (Bächli et al., 2002; Bächli, pers. comm.).
Other alien Diptera occurring in Switzerland are saprophagous or coprophagous. These
species are often of cosmopolitan distribution. The calliphorid Chrysomya albiceps and
the muscid Hydrotaea aenescens are found on human cadavers and other decaying
matters. The black soldier fly, Hermetia illucens (Stratiomyidae), was found in very
high numbers in composted plants in the Ticino (Sauter, 1989). In North America, this
very common species is often associated with poultry houses and other farming or
animal-rearing activities. Only one milichiid, Desmometopa varipalpis, is mentioned in
our list as clearly exotic. However, the Milichiidae are small, often cosmopolitan and
Advisors:
Bernhard Merz, Muséum
d’Histoire Naturelle, Genève;
Jean-Paul Haenni, Muséum
d’Histoire Naturelle, Neuchâtel;
Gerhard Baechli, Zoologisches
Museum, Zürich; Wolfgang Billen,
Amt für Landwirtschaft, Lörrach,
Germany