Phenological features of elm leaf beetle in vegetation of Kharkiv City

Abstract

Introduction

Elm leaf beetle (Galerucella luteola M?ller, 1766: Coleoptera: Chrysomelidae) is one of the most significant phyllobionts of the genus Ulmus. It is spread widely, particularly in the Steppe and Forest-Steppe zone. The damaged trees here have weakened, the branches have been damaged by frost, colonized by bark beetles and infected by Dutch elm disease.

The aim of the research was to reveal the features of elm leaf beetle development in green stands of Kharkiv.

Materials and Methods

The trees of Ulmus laevis Pall., U. glabra Huds., U. minor Mill. and U. pinnato-ramosa Dieck. were inspected in 2018–2019 in parks, squares, along highways and city streets. Insect identification and rearing were carried out in the Laboratory of Forest Protection of the Ukrainian Research Institute of Forestry and Forest Melioration named after G. M. Vysotsky.

Results

The highest population density rates of elm leaf beetle were recorded in Molodizhny Park and in the square of the House of Culture of the Kharkiv Electromechanical Plant, as well as in the Forest Park, along Zhuravlivsky Descent and Kharkiv Regional Ring Road.

Adult beetles overwinter in the litter, sometimes in soil, in the bark cracks or hollows. They began feeding at the time of elm foliage blooming, namely in early May in 2018 and in late April in 2019. The beetles damage young foliage, using it as maturation feeding. They browse the holes of different shapes and sizes, sometimes consume secondary veins, at that, they always leave the main vein.

The egg masses were found in the 3^rd decade of May in 2018 and in the 2^nd-3^rd decades of May and in the 1^st decade of June in 2019. The larvae appeared at the end of the 1^st decade of June in 2018 and in the 3^rd decade of May in 2019. The larvae could be found up to the beginning of July. They skeletonize leaves for 18–29 days and molt twice. The larvae pupate in the litter, sometimes in the tree crown. It develops for about 10 days.

The beetles of the 1^st generation appeared in the trees in the first decade of July in 2018 and at the end of June in 2019 and carried on maturation feeding up to the end of August. Then they mated and laid eggs. In 2018, the beetles of the 2^nd generation were found in the 2^nd decade of August, and in 2019 the eggs of the 3^rd generation were laid in the 1^st decade of August. The larvae appeared in the middle of August and pupated on September, 2. The beetles of the 3^rd generation were found on September, 8.

Conclusions

Depending on weather conditions, 2–3 generations of elm leaf beetle per year may develop in Kharkiv. Beetles hibernate in bark crevices, hollows, or in the litter. They leave the wintering places during elm leaves blooming (in late April – early May). The egg-laying period is extended, generations overlap. Development of eggs lasts for 6–10 days, larvae develop during 18–29 days, pupae – about 10 days. The phenological calendar for elm leaf beetle is compiled as the result of the research.

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