New Pest Response Guidelines - aphis - US Department of Agriculture

Pest Information
Egg
Development normally takes 13-15 days with a maximum of 20 to 22 days
(EPPO, 2005).
Larva
During a typical two-calendar year cycle the number of larval stages for the
SSM will vary between five to eight for males and six to nine for females
(Baranchikov et al., 1997; EPPO, 2005). First instar larvae molt 9-12 days after
emergence. Second instar larvae will develop in 3-4 weeks. The larvae
overwinter as second or third instar larvae. In the second year, larvae will
either complete development into adults, or will undergo a second winter
diapause as fifth or sixth instar larvae on the forest floor. One month after the
last winter diapause, the fifth instar larvae molts to sixth instar and complete
regular development (EPPO, 2005).
Variations in developmental time for the SSM have been observed in different
populations that develop in the same geographic location, some of which
complete their life cycle in one, two or three years depending on the local
temperature conditions (Galkin, 1993) (Figure 2-5 on page 2-22). It has been
also observed that a population can switch from a one to a two year cycle based
on weather conditions (Galkin, 1993). During warm summer and fall seasons,
the larvae will grow and molt more readily than those growing in cold summer
and fall conditions (Galkin, 1993). Another important factor affecting
developmental time is the photoperiod. Long days will accelerate development
and days with a LD of 12:12h will stimulate diapause (Geispits, 1965). The
combination of long days with warm summer and fall temperatures is ideal for
the fast development of both the SSM and the SaSM, a condition that also
applies to one of their primary host species, Larix spp. (Galkin, 1993). Winter
conditions for normal moth development require no autumn thaws, which
would be fatal for the hibernating larva (Baranchikov et al., 2009).
One of the most important physiological factors affecting the development of
the SSM is the presence and timing of summer diapause (Baranchikov and
Kirichenko, 2002). Although it is known that winter diapause is triggered by
photoperiod in the fall, the causes that initiate summer diapause in the SSM are
not well understood. During summer diapauses, the time spent as a fourth
instar larvae increases by 50%, probably as an outcome of a reduction in food
consumption and assimilation compared to larvae that do not diapause
(Baranchikov and Kirichenko, 2002). Larvae that overwinter as second instars
in the first year of their development are not able to fully complete their life
cycle in the following year and therefore diapause, or delay growth, in the
summer to overwinter as fifth or sixth instars and complete the cycle in the
third year, after the second overwintering period. This synchronization is
essential to increase the probabilities of mating when the adults emerge
(Baranchikov and Kirichenko, 2002).
12/2012-01 Dendrolimus Pine Moths 2-27