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ŠUMARSKI LIST 3-4/2009 str. 49     <-- 49 -->        PDF

M. Pernek, D. Matošević: BAGREMOVAMUHAŠIŠKARICA(Obolodiplosis robiniae) – NOVI ŠTETNIK ...Šumarski list br. 3–4, CXXXIII (2009), 157-163
SUMMARY: Black locust gall midge (Obolodiplosis robiniae) (Diptera:
Cecidomyiidae) is the most recent invasive species in Europe originating, like
its host plant, from North America. It started its quick spread in Europe in
2003 from the Veneto region in Italy where it was first found. Platygaster robiniae(
Hymenoptera: Platygastridae), parasitoid of the midge was first described
as species in 2008. In the researches of the black locust gall midge only
one record was given for Croatia (in 2006) but without details. The aim of this
research was to record the distribution, biology, parasitoids and damages of
this newly introduced insect species in Croatia.


The presence of black locust gall midge was recorded by inspection of
black locust leaves on the following localities: the greater surrounding of Zagreb,
Jastrebarsko, northwestern (Đurmanec, Lepoglava, Ivanec), submediterranean
(island Krk) and mediterranean (surrounding of Zadar) part of
Croatia (Table 1). The presence of larvae and parasiotids in galls was researched
on the sites in Zagreb. On 9 July 2008 a sample of 20 black locust
leaves was taken from 3 trees and analised. Galls (Figure 1) with white (Figure
2) and yellow larvae (Figure 3) were found on the leaves. White larvae
are young and yellow older instars.


In the sample of 20 leaves i.e. 251 leaflets of black locust 599 galls were
found which is 2,3 galls on average per leaflet. Total number of larvae was
1183 or 2 larvae on average per gall, out of which yellow larve (916) were numerous
than white (82) (Table 2). Parasitised larve (Figure 4) and cocoons of
parasitoidPlatygaster robiniae(Figure 5) were found in galls. The percentage
of parasitism of black locust gall midge in the sample was 15,6 % (Table 2).


The black locust gall midge can be cosidered as a new invasive species in
Europe as well as in Croatia. The midge was very probably introduced to Europe
with planting material and its main vectors of dispersal in Europe were
black locust ornamental plants trade and intensive international vehicle transport.
The dispersal in Croatia had two main entries: from Slovenia and Hungary
for the continental part and from Italy for the Mediterranean part.


The observations of the black locus midge biology in the northwestern
Croatia in 2008 have not shown the development of new generation after July.
The last larvae in galls were found on 9 July. Our own observations and different
data on overwintering of other researchers have shown a need for more
researches of the various aspects of black locust midge biology (number of generations,
overwintering).


In the galls of the black locust gall midge the parasitised larvae (Figure 4)
and cocoons of parasitoidPlatygaster robiniae(Figure 5) were found on all
localities of research in Croatia. This is the first record of this species in Croatia.
From the percentage of parasitism of 15,6 % it can be presumed that the
midge is present in Croatia for several years (which confirms the record from
2006) and that the parasitoid has successfully adapted itself to the new pest.
In the next year a more intensive spread of black locust gall midge in Croatia
can be expected, but also a multiple rise in parasitism levels.


Black locust gall midge makes distinctive damages on leaflets of black locust
- galls (Figure 1). Numerous galls on leaflets influence the assimilation
process and can cause premature leaf drop. The galls influence the aestethic
value of black locust ornamental plants. The estimation of damages caused by
the midge vary considerably in Europaean countries. Black locust is not an
important forest species in Croatia so the black locust gall midge is not considered
as important forest pests. Aesthetic damages can be expected on ornamental
plants.


Key words:black locust, new introduction, damage, Diptera: Cecidomyiidae,
Hymenoptera: Platygastridae