Liriomyza nietzkei Spencer, 1973
INTRODUCTION
Spencer, 1973 raised nietzkei, recognized as an unnamed subspecies by Nietzke, 1944 to species level.
On the group of Allium feeders
In external view the three Liriomyza species feeding on Allium (cepae, nietzkei and chinensis) are untypical members of the genus and can be confused by the unusually dark appearance and black scutellum. However, the male genitalia are sufficiently distinct. A further hint might be the angulate third antennal segment.
To separate the species within this group; the investigation of the male distiphallus is necessary.
IMPORTANT CHARACTERS
Wing length: 1.6 - 1.9 mm. This species is closely related to Liriomyza cepae and Liriomyza chinensis but the genitalia are distinct. The terminal tubules of distiphallus are shorter than in cepae and straight.
BIONOMICS
The life cycle and bionomics was investigated by Nietzke, 1954 (as 'Herxheim race' of Dizygomyza cepae). As the other Liriomyza miners on Allium the larvae dwell in the leaves and the stem layers of the plant. Probably they are able to change the layers within the host plants. Pupariation occurs in the soil. Nietzke reported only one generation for Germany, the flies emerge in May and remain abundant until July. Correlations between observed peak abundances and both high temperatures and low humidity were observed. In contrast SÜss, 1975 reported two generations in Italy, the latter of which, however, cause lesser damage than the first.
Both Nietzke, 1954 and SÜss, 1975 observed that a part of the males are as small as 10% or even smaller.
The fully grown larvae in search for a proper site for pupariation, "like many in this genus, can jump by coiling themselves up and by quickly releasing the tension throw themselves several centimetres through the air. This procedure takes place several times prior to pupation." (Spencer, 1973)
HOST PLANTS
Allium cepa (onion), Allium porrum (leek) and possibly other Allium species.
DISTRIBUTION
Germany, France, Italy, probably widespread in Europe.
ECONOMIC IMPORTANCE
Because of possible taxonomic confusions species records concerning leaf miner damage on onion should be handled with care, especially those from before 1973, when Spencer's book on agromyzids of economic importance appeared. The Liriomyza species causing the damage can be either Liriomyza cepae, Liriomyza chinensis (especially in the Eastern palaearctic region but also in Europe), or Liriomyza nietzkei (especially in Europe).
If they occur in large numbers all of these species have the potential to cause severe damage and are treated as serious pests by most authors (see literature). The larvae weaken the plants in destroying leaves. However, outbreaks seem to be rather intermittal and local.