Effects and Impacts

Invasiveness and Phytosanitary Risk / Risk of Introduction

Lymantria monacha is considered to be the number one forest pest in Poland because of the unprecedented economic losses it causes in spite of intensive chemical protective treatments on an area of 6.3 million ha of pine, spruce and other conifers between 1978 and 1984 (Sliwa and Sierpinski, 1986).  It is also considered to be a major pest in all the other areas where it goes through periodic outbreaks causing defoliation and resulting in the death of spruce and pine trees (Bejer 1988).  The frequency of outbreaks has declined from about every 30-40 years to intervals of 6 years.  It poses an ever present threat of being accidentally transported via commerce and introduced into other world areas where susceptible hosts are present for a couple of reasons: adults are readily attracted to artificial lights and have been observed in Russian Far East ports (Munson et al., 1995), and although eggs are normally laid in bark crevices, they also could be deposited in crevices on containers, pallets, ships, etc.  In a pest risk assessment for importation of larch from Siberia into the United States, L. monacha was one of the serious pests that were considered at risk of introduction if the bark was still on the logs because of their use of the bark for oviposition and the fact that the eggs are not readily visible (Anonymous, 1991).   Its establishment in areas with suitable hosts would be disastrous because of its polyphagous feeding habits, ability to colonize new habitats, and capacity to be spread rapidly by flying females.  

Lymantria monacha is listed as an invasive species of concern by the United States Department of Agriculture; port inspectors monitor for it and as part of the Rapid Detection Pilot Project pheromone traps are being placed near ports of entry to detect any breeding populations.  There were no L. monacha trapped in the one season of United States port monitoring reported on so far.  Population levels are being monitored through collaboration between United States and Russian agencies in the Russian Far East near ports (Munson et al. 1995).

Impacts

Economic impact

The first recorded outbreak of Lymantria monacha(1853-1863) occurred in European Russia and resulted in the damage or destruction of about 403,000 km² of forest (Bejer, 1988).  Since then there have been periodic outbreaks across Europe (Wellenstein, 1942a, Bejer, 1988, Schoenherr, 1989, Lipa and Glowacka, 1995).  During the longest (19780-1983), over 2 million ha of coniferous forests (one quarter of Poland’s forests) were infested and partly defoliated (Schönherr, 1985).  In addition, L. monacha defoliation has been shown to reduce annual tree growth in pines in Poland (Beker, 1996) and spruce in Czech Republic (Vins and Svestka, 1973).  The cost of eradication or control of L. monacha, based on host plant availability and climate, would be enormous should it become established in North America (Wallner 1996).  

Environmental impact

Lymantria monacha damage and resulting tree loss has the potential to alter the species composition of forests where outbreaks occur.  The loss of coniferous species would be more severe than that of deciduous species because they tolerate less defoliation.  Any associated wildlife that depends on the affected tree species for food or nesting would be adversely affected.  Nutrient and water cycling in the ecosystem may also be affected.  During a L. monacha outbreak In Poland, the massive quantities of frass and needle fall increased the nitrogen and phosphorus in the pine litter two to three times the normal level and also increased the potassium and manganese significantly (Dziadowiec and Plichta, 1986) 

Social impact

Coniferous trees killed by Lymantria monachadefoliation or subsequent attack by other organisms may not be useable for lumber because of deterioration of the wood before it can be harvested.  This could affect the timber industry and those they employ.  Tree loss, especially in populated areas, can also affect tourism and increase safety concerns in areas where dead limbs or trees could fall and injure people or damage property.  The scales and hairs of L. monachaare allergens so outbreaks can create a human health risk for some people (Delgado, 1978).

For further details log on website :
https://www.nrs.fs.fed.us/disturbance/invasive_species/nun_moth/effects_impacts/