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ŠUMARSKI LIST 1-2/2013 str. 55     <-- 55 -->        PDF

The fine feeding of caterpillars of the 1st instar, which could not be detected by this apparatus, was determined in a biometric laboratory by means of the system of analysis and image processing NIS – Elements AR (digital camera 5 Mpix Nikon DS – Fi 1 with Navitar macroobjective, exposure KAISER RB 5000 DL, exciter lamp KAISER prolite basic, computer with NIS program – Elements AR, version 2.30, processor X86, 2533 MHz, HD 230 GB, RAM 2 MB). The system operated in the MS Windows XP Professional environment (Kula et al., in print).
After the experiment termination, the content of nitrogen was determined in remainders of leaves of B. pendula from the period of the whole rearing in a 14-day interval. To evaluate data obtained the program was used (StatSoft 2007).
The content of nitrogen in birch leaves – Sadržaj dušika u lišću breze
The level of nitrogen in leaves of control birch trees (T0) was markedly lower in comparison with leaves of fertilized treatments (T1–T3). Maximum values were achieved in the first 14 days of rearing (28.21 mg.g–1), then a continuous decline occurred to a minimum value in the final stage of rearing (17.17 mg.g–1). The content of nitrogen in leaves of treatment T1 decreased from a maximum at the beginning of the rearing (33.91 mg.g–1) to a value of 27.38 mg.g–1 (26 May – 9 June) with a subsequent slight increase to 29.82 mg.g–1. The content of nitrogen in leaves of birch treatment T2 ranged within the limits 30.38–36.25 mg.g–1 and at treatment T3 within the limits 32.35–38.89 mg.g–1, maximum values being determined at the beginning of the rearing (Fig. 1).
Mortality of caterpillars – Mortalitet gusjenica
Hatched caterpillars of L. dispar in the laboratory rearing in control treatment showed 30.7 % mortality. However, at caterpillars fed on food with the higher content of nitrogen (treatments T1–T3), we determined 2.7–4 % mortality. Differences in the mortality of caterpillars within a 48-hour interval between treatment T0 and treatments T1–T3 were statistically significant in the first 10 days of rearing (p = 0.010–0.013) (Fig. 2).
In control treatment, the mortality of caterpillars continuously increased up to a level of 40.0 % until the 40th day of rearing where it remained until the end of the rearing (40.7 %) (Fig. 3). Caterpillars of the 1st instar were most sensitive in the control treatment (31.3 %). In the consequential 2nd – 6th instars, the decline gradually stopped (6–3.3–0–0–0 %).
The mortality of caterpillars in treatment T1 after 20 days of rearing increases to 5.3 %. After 30 days of rearing, it reaches the final value of 6 % while 3.3 % caterpillars died in the 1st instar and 2.7 % in the 2nd instar.
Mortality in treatments T2 and T3 remained at the initial level (3.3–4 %) in the first 20 days of rearing and differed significantly (p = 0.022) from the increasing mortality in treatment T1 (Fig. 2). In further 10 days, it doubled (7.3–8 %). In treatment T3, the value of 7.3 % is final while mortality in T2 increases up to 9.3 % (Fig. 3). In treatment T3, caterpillars died only in the 1st (3.3 %) and 2nd (4 %) instars while in treatment T2, dead caterpillars occur also in the 3rd and 4th instars.