©
iForest -Biogeosciences and Forestry
IntroductionNorway spruce is the second most abundant tree species in Latvian forests, occupying 0.52 million hectares, and nearly 0.14 million are second age class (21-40 years old) forest stands (Latvian State Forest Service 2011). Therefore, it is critical to assess the management risks in growing stand volume now, because it is these stands that will comprise the majority of the cutting volume in 40-60 years. Spruce is a species quite vulnerable to biotic and abiotic factors; therefore its cultivation is increasingly associated with high-risk levels. One of the most widespread causes of Norway spruce stand damage is development of large spruce bud scale colonies.The first cases of Norway spruce damage were observed in 2009 in middle-aged stands on drained soils. In August of 2010, monitoring by Riga Forests revealed 24% of the stands were damaged, and 10% of Picea abies stands were reported dead. Management made the decision to avoid further spruce bud scale propagation by felling 300 ha of Norway spruce forests in sanitary clear-cuts . Physokermes piceae Schrnk. belongs to the Coccidae family, order Hemiptera, and are characterized by sexual dimorphisms, with a high ability to adapt to a parasitic lifestyle on host plants (Rasina & Rupais 1994). Adult females are globular with a pronounced curvature, shiny, and brown to reddishbrown in color. Female length averages 3.5 mm, width 3.0 mm, and height 3.5-4.0 mm.Males are winged, average 1 mm long, and rarely encountered (Ozols 1985). Males have a discernable head, chest and abdomen, three pairs of legs, and one pair of wings (Graora et al. 2012). The species develops one generation per year. Immature stages winter at the base of terminal buds, less often on needles. In May, the instar larvae move to the base of new buds by old bud fissures. By the end of May or beginning of June, the females have already developed. Settling on the trunk and twigs, individuals suck sap through the bark vascular tissue. At the end of June or beginning of July, the insects lay eggs beneath themselves, and soon die (Ozols 1985). Several studies report one female lays 800-3 000 reddish eggs (Novak 1974, Turguter & Ülgenturk 2006, State Forest Service 2010. Pink first instars, called "crawlers" hatch in July, and attach themselves to new buds or the underside of needles. In October, crawlers molt into the second instar, and change color from pink to brown. The second instar larvae continue to suck sap, and subsequently overwinter on the branching parts or the lower side of the spruce needles. In spring, a small portion of the overwintering population travels to the needles, where in May the individuals pass through prepupal and pupal stages, developing into winged males (State Forest Service 2011, Lazdins et al. 2011. After wintering, most second instars attach themselves among the budding forked branch apices, where molting occurs, and round yellowish females emerge that gradually darken, and are easily noticeable (State Forest Service 2010.Sp...
