DIGITALNA ARHIVA ŠUMARSKOG LISTA
prilagođeno pretraživanje po punom tekstu
| ŠUMARSKI LIST 7-8/2014 str. 35 <-- 35 --> PDF |
The embryonic development duration was determined in the period from April 8th to April 21st, 2008 on the sample of 100 eggs. In the plastic box with ash weevil adults in the morning were placed shoots with undamaged buds. Meantime laid eggs, were collected under the stereo microscope in the early afternoon from the buds and placed onto the wet filter paper to prevent them from drying. The embryonic development duration was determined by daily observation and under uncontrolled outdoor conditions. The larval development was determined by individual growing of 40 larvae in period from April 19th to May 15th, 2008. Larvae were grown in Petri dishes with a diameter of 9 cm and a height of 1.2 cm in uncontrolled outdoor conditions. The number of larval stages, duration of development of individual stages and the total duration of larval development were determined by daily observation. Larvae were fed with leaves of narrow – leaved ash. The quantity of food consumed by larvae was expressed as difference between leaf area of leaves before and after feeding measured by the meter of leaf area (ADC Bioscientific Ltd., AM300). Duration of the pre-pupa and pupa stadiums was determined by growing 50 pre-pupas and pupas, which were cut out by scalpel from newly formed cocoons during the period from the 1st to 6th of May, 2008. After that insects were placed in Petri dishes on wet filter paper and by daily control was determined duration of pre-pupa and pupa stage. Experiment was established under outdoor conditions. Duration of additional feeding for overwintering and the quantity of food consumed by adults before entering the diapauses were determined by separate growing of 25 adults of new generation from June 1st, 2009 in outdoor conditions. Adults were grown in plastic Petri dishes with a diameter of 9 cm and a height of 1.2 cm, where one undamaged leaf was placed in. Every two days the leave was changed by new undamaged one. Adults were fed on narrow – leaved ash leaves and the quantity of food consumed by larvae was expressed as difference between leaf area of leaves before and after feeding measured by the meter of leaf area (ADC Bioscientific Ltd., AM300). In order to determine the number of generations at the end of May, 2007, 20 adults of new generation were grown on narrow – leaved ash plants planted in five pots and covered by the net. Adults were grown immediately after eclosion. Plants were observed on regular basis in order to register eventual development of new (second) generation of insects. Experiment was established under outdoor conditions. 3. Results Rezultati First ash weevil adults were observed on the branches in Branjevina forest at the beginning of the second decade of March in 2008, and a larger number of overwintered adults was found during April (Figure 1). In early May the number of adults declined suddenly and from the mid May with the occurrence of the new generation of adults their number increased again and reached a maximum at the end of May. Adults continued to occurred until the end of June. In 2009, the first adults were confirmed in early April (Figure 2), and further presence of adults in the ash canopy greatly coincided with the number found in 2008. After leaving their winter shelters, adults began with feeding by feeding on buds first, and later after flushing they fed on young shoots and leaves. First copulations in 2008 were observed at the end of March. Numerous copulations were |