New Pest Response Guidelines - aphis - US Department of Agriculture

Pest Information
Dendrolimus sibiricus
Outbreaks of SSM are periodical and occur on average every 10-11 years
(Baranchikov et al., 1997; Orlinskii, 2000). Outbreaks have been strongly
correlated to cycles of solar activity (Galkin, 1975). Climatological factors
such as rain and amount of snow during the winter play an important role in
regulating the populations of SSM. A shallow snow cover during the winter
can cause high mortality on hibernating larvae because of inadequate
insulation to the extreme temperatures during the winter.
Elevation, slope steepness and altitude are topographical characteristics that
affect the severity of an outbreak. Kharuk (2007) found that the most severe
defoliation and tree mortality was observed at an elevation between 200 and
310 meters. Slopes with southwestern exposure receive more solar radiation
which creates drier and warmer conditions, favorable for larval development.
Maximum damage was observed on slopes between 5° and 20ºC ( Kharuk et
al., 2007). The highest concentration of SSM larvae is normally found on the
hill tops (Liu and Shih, 1957) a place that is more effective for females to
disperse their pheromones, attract males, mate and lay their eggs (Li et al.,
1987).
The development and intensity of an outbreak is also dependent on the forest
species composition and abundance. Outbreaks in Larch forests normally last 2
years until trees are completely defoliated but because of the high resistance of
Larix trees to both moth species, these outbreaks will not result in high tree
mortality and very rarely, affected trees are attacked by secondary pest like
insect borers (Averensky et al., 2010; Baranchikov et al., 1997; Rozhkov, 1970
). In exceptional cases, when the outbreaks last more than two years, possibly
due to extended developmental time of the larvae resulting from insufficient
amounts of food and malnutrition, some tree mortality can be observed
(Rozhkov, 1970). In contrast to Larch forests, other coniferous forests are more
susceptible to outbreaks and tree mortality followed by secondary pests attack
and forest fires are more common (Rozhkov, 1970). The severity of the
outbreak is also determined by the age of the forest stand. SSM outbreaks are
more severe when the forest is composed primarily of trees older than 15 years
(Li et al., 1987 ).
Dendrolimus superans
Outbreaks of SaSM are normally preceded by two to three years of drought
with mean summer temperatures above the normal average (Maeto, 1991). In
Hokkaido, Japan, major outbreaks of D. superans were normally preceded by
three years of summer temperatures 1ºC higher than the normal temperatures
(Maeto, 1991). Excessive rainfall can cause high mortality of first instar larvae,
the most vulnerable of all larval stages (Maeto, 1991).
12/2012-01 Dendrolimus Pine Moths 2-35