10. The level of threat to forests posed by the more important folivorous insect species -
Jadwiga Ma豉chowska, Andrzej Kolk
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Polish forest like the forest of many other countries are prone to the damaging effects posed by insect pests. The poor composition of tree species and other stand characteristics combined with weather conditions and pollutant deposition are the main factors favouring outbreaks of folivorous insects. This entails an every-year monitoring of population abundances of the most harmful insect pests in the forests.
The analysis of a threat to forests posed by the more important species of insect pests is based on results of capturing male nun moths and evaluation of abundance of other folivorous insect pests and pine-shoot beetles made on the first-level POPs in coniferous stands over 40 years old.
The nun moth is one of the most dangerous insect pests. Its abundance during the last five years was variable - Fig. 11.
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In 2003, the abundances of this pest in the Silesian (252.9), Mazowsze-Podlasie (239.8), Ma這polska (219.8) natural-forest regions were remarkably higher than the average countrywide - Fig. 12. It could be stated that 2003 saw again a considerable threat posed by nun moth in many regions of the country.
Pine beauty moth is one of the most dangerous pests of pine stands. In 2002-2003, the abundances of this species were insignificant in the majority of the natural-forest regions. In 2003, the largest number of these insects was found on the plots in the Carpathian and Mazowsze-Podlasie natural-forest regions.
Pine sawflies are the dangerous pests of pine, which recently have posed a threat to forest. 2003 saw a decrease in abundances of this pest and the country mean decreased. Elevated abundances were noted on POPs located in the Mazowsze-Podlasie, Ma這polska and Carpathian natural-forest regions.
Pine looper moth is another dangerous folivorous pest. In 2003, the increased abundances of this foliophage ware noted in the Silesian and Wielkopolska-Pomerania natural-forest regions.
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The abundance of the pine hawk moth in 2003 slightly decreased - Fig. 13. The mean population abundance for the country was 0.39. The elevated abundance of this pest over the last five years was reported in the Wielkopolska-Pomerania and Mazowsze-Podlasie natural-forest regions.
The abundance of the pine lappet moth remains low over the prevailing area of the country. In 2003, it drastically increased and exceeded the warning figures for this pest.
The country mean abundance of the pine webworm ranged from 0.24 to 0.73 individuals per plot. In 2003, the highest abundances were recorded in the Mazowsze-Podlasie, Silesian and Ma這polska natural-forest regions.
Pine-shoot beetles are the most frequently encountered secondary pests of pine stands. In 2003, the largest numbers of shoots damaged by pine-shoot beetles were collected on POPs located in Mazowsze-Podlasie (9.1) and Mazury-Podlasie (8.0) natural-forest regions.
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The abundances of folivorous insects are on the level which does not pose threat to forest stands. The highest increase in nun moth abundance was reported in Silesian and Ma這polska natural-forest regions. Elevated abundances of pine sawflies were found in the Carpathian natural-forest region, pine webworm - in the Silesian region and pine hawk moth in the Mazury-Podlasie and Carpathian regions. The abundance of the pine lappet moth drastically increased in the Ma這polska natural-forest region. Increased population abundances of pine looper moth were noted in the Silesian and Carpathian natural-forest regions. |