THE OCCURRENCE AND HARMFULNESS OF PHYLLONORYCTER ROBINIELLA (CLEM.), A NEW LEAFMINER OF ROBINIA PSEUDOACACIA L. TREES

Elżbieta Wojciechowicz-Żytko, Beata Jankowska

ABSTRACT

The North American species – Phyllonorycter robiniella (Clem.) – which mines the leaves of Robinia pseudoacacia L. was reported from Europe in 1993 for the first time. It was discovered in Poland in 1999. Caterpillars feeding cause premature leaf fall due to its desiccation, which negatively influence the aesthetic appearance of the trees.

Key words: Robinia pseudoacacia, Phyllonorycter robiniella.

INTRODUCTION

Black locust (False Acacia) – Robinia pseudoacacia L. – is native to North America and was introduced to Europe in the early 17^th century as an ornamental tree and now became an important tree in forest plantations in France, Italy, Hungary, Romania and Poland. Is planted extensively for its nitrogen fixing abilities, as a source of nectar for honeybees, and excellent wood for firewood. It is also used for erosion control and mine soil reclamation.

R. pseudoacacia is being valued element of green areas of Kraków. It is situated individually, in loose groups or rows in parks or near streets. It has very limited soil requirements as well as high resistance to city and industrial pollution and dry periods.

Phyllonorycter robiniella (Clem.) is the main pest of R. pseudoacacia leaves. It comes from the eastern and central western part of the USA [4]. It was first time reported from Europe in Basle (Switzerland) in 1983 and from it extended to Central Europe – France, Germany, northern Italy (1988), Austria (1989), Czech Republic and Slovakia (1992). It spread gradually through Austria, reaching Hungary in 1996 [3, 6, 7, 10]. In 1999 it was first recorded in Poland (Katowice, Opole, Wrocław) and it occupied the southern region of Poland to 2000 [2]. In 2001 it was found in Józefów near Warszawa [9].

P. robiniella causes premature leaf drop due to its desiccation and negatively influence the aesthetic appearance of the R. pseudoacacia trees.

Regardless of the mass attack of R. pseudoacacia by P. robiniella only a limited number of papers has been published so far [1, 3, 4, 5, 6, 7, 8].

This paper provides new data on the occurrence and harmfulness of Phyllonorycter robiniella in Kraków area.

MATERIALS AND METHODS

The observations were carried out in Krakow, in September in 2002 and from June to September, in month intervals, in 2003, on Robinia pseudoacacia and Robinia pseudoacacia ”Umbraculifera” trees. Six trees growing in the parks, alleys and near the street traffic were chosen for the study.

Site A – Robinia pseudoacacia – park site – (group of trees),
Site B – Robinia pseudoacacia – green area in the centre of the city (individual tree),
Site C – Robinia pseudoacacia – green area in housing estate-(few trees),
Site D – Robinia pseudoacacia – row of trees along the street (high traffic),
Site E – Robinia pseudoacacia “Umbraculifera”– row of trees along the street (high traffic),
Site F – Robinia pseudoacacia “Umbraculifera” – street site (high traffic) (individual tree).

From each tree 20 pinately compound leaves (each possessed 7-19 leaflets) were collected and the infestation by the P. robiniella (the presence of mines) were estimated. Later, these leaves were divided on the single leaflets, and the number of leaflets of all compound leaves from each site was counted, and infestation by P. robiniella was noted. Subsequently, the 100 leaflets from the each tree were evaluated on the occurrence of the P. robiniella caterpillars, pupae, moth’s, and its parasitoids.

RESULTS AND DISCUSSION

Bionomics of Phyllonorycter robiniella (Clem.)

The adults hatched from the collected pupae were tiny moths with a wingspread of about 5-6 mm. Wings were brownish with golden – beige pattern (phot. 1, 2).

According to Šefrová [7] eggs are elongate, bright grey-greenish and the larval development comprises 5 instars. Based on the analysis of the leaves it was noted that the first caterpillar instars were yellowish, whereas the last was greenish (phot. 3, 4). Šefrová [7] working on the morphology of P. robiniella caterpillars noted that first three instars were flat, with reduced legs, and last two instars had normal shape legs.

On the observed R. pseudoacacia trees, the females have oviposited on the underside surface of the leaf and the caterpillar initially formed a narrow tunnel, which next became flat and white spot (phot. 5, 6). The final mines have combined and occupied whole underside surface of the leaf and sometimes also appeared on the upperside of the leaves. In these mines it was possible to found even 8-12 caterpillars. The pupation followed in a circle, thick, silky cocoon (phot. 7, 8).

According to Šefrová [7] P. robiniella develops 2-3 generations during the vegetation period in central Europe (the complete development lasts 5-11 weeks), whereby the last generation moths hibernate.

Based on our observations the hibernating moths have oviposited at the end of May after the full foliation of R. pseudoacacia and first mines of the 1^st generation occurred in the beginning of June. Moths of this generation were observed in mid June.

The moths of summer generation appeared in mid-July. During the days the high amount of moths sitting on R. pseudoacacia leaves were observed.

The moths of next generation were flying in mid August, reaching their peak in the 3^rd decade of August. During this time many empty pupae errected from R. pseudoacacia leaves were noted (phot. 9).

Probably the moths of this generation hibernated in the bark crevices, under the bark or in other similar places.

The occurrence of Phyllonorycter robiniella (Clem.) in Kraków area

The analysis of 120 in the autumn 2002 and in year 2003 – 480 compound leaves from the trees growing in the different parts of Kraków shown that the large amount of P. robiniella was noted on the all tested trees. In 2002 all compound leaves were infested by P. robiniella, and the mean infestation of the single leaflets was 94% (tab. 1), whereas in 2003 the infestation of the leaflets reached 15.7% in the spring and 92.8% in the autumn (tab. 3).

Each mine contained caterpillars from 1^st to 5^th instars and also silky cocoons of P. robiniella. In the final mines the pupae of the parasitoids was also visible (phot. 10). The development of each stage, depended on the environmental conditions e.g. temperature, humidity and pollution [7], varied on different sites. The results are presented in table 2 and 4.

In the year 2002 the highest number of P. robiniella caterpillars was recorded on the park site A (area outside of the city) whereas the largest amount of its pupae occurred on the site B (green area in the centre).

In the year 2003 the total infestation of the robinia trees also varied between the sites of observations (tab. 4). The highest number of caterpillars and pupae were found on the site B (green area in the centre) and on the site F (street site – big traffic).

During the vegetation season the maximum of caterpillar’s occurrence were noted in August (fig. 1). In this time P. robiniella catterpillars formed oval – shaped mines also on the upperside of the R. pseudoacacia leaves. During this period due to the high infestation the premature leaf fall and the development of the young leaves from the winter buds were observed on sites A, B, E, F. In September the initial narrow mines on these leaves were found (phot. 5, tab. 5).

In the year 2002 the parasitation reaching 37% was noted (mean 17.36%). The lowest number of parasitoids pupae was found on site A whereas the highest on the site B.

In the year 2003 the parasitation of P. robiniella varied from 2% in June to 39.5% in autumn.

The parasitoids were the little wasp species (phot. 11). Šefrová [7], working on the bionomics of P. robiniella, noted the parasitation from 10 to 30%. Whitebread [10], Deschka [4] informed of altogether 7 parasitoid species, all belonged to the Eulophidae and Braconidae families.

CONCLUSIONS

The above observations pointed out the importance of the Phyllonorycter robiniella as a new pest of R. pseudoacacia trees. Monitoring the next spread and density of this insect as a new member of the Polish insect’s fauna appears to be important and useful. It is necessarily to continue above study by a bionomics, population dynamics and the natural regulation of abundance of this pest.

REFERENCES

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2. Buszko J., Nowacki J., 2000. The Lepidoptera of Poland. A Dirtributional checklist. Polish Ent. Monogr. 1, 1-178.

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