New Pest Response Guidelines - aphis - US Department of Agriculture

Pest Information
There is a noted effect of host type on larval development for the SSM. Choice
tests show that the SSM prefers and develops faster in Larix spp. than on those
considered to be poorer quality hosts: Abies spp., Pinus spp., Picea spp. and
Pseudotsuga menziesii (Kirichenko et al., 2006; Kirichenko et al., 2009b).
Larvae fed on Larix were on average three times heavier, had a shorter
developmental time and the lowest mortality rates compared to those reared on
pine species, particularly P. sylvestris and P. nigra (Kirichenko et al., 2009a;
Kirichenko and Baranchikov, 2007). Mortality rates of larvae reared on P.
nigra were as high as 83% compared to 3.2% in Larix spp. (Kirichenko et al.,
2008a). It is worth noting that larvae fed on Douglas-Fir, a species of economic
importance in Europe and North America, had a development and mortality
rate comparable to those reared on Larix (Kirichenko et al., 2008a). Compared
to other Pinacea, needles from Larix have lower essential oil content and
higher nitrogen, water and fiber content, a nutritional condition that might
favor development and reduce mortality of SSM larvae (Vshivkova, 2004).
Variations in optimal population densities can have an effect in the
development, mortality and the physiology of the SSM, and competition for
food in populations with high density may extend the developmental time of
the larvae and increase the number of instars (Kirichenko and Baranchikov,
2004 Ghent and Onken, 2003). The mortality rate of first instar larvae reared in
large numbers (n=20) was reduced 20-fold when compared to individually
reared larvae (Kirichenko and Baranchikov, 2004). Population density also
affects the duration of development, but studies are mixed on the timing of the
effects. Although the duration of development was not affected in first and
second instar larvae reared either in groups or isolated, third and fifth instar
larvae developed faster and gained more weight when reared in groups
(Kirichenko and Baranchikov, 2004). The efficiency of utilization of food (i.e.,
the measured fraction of assimilated food that turns into tissues) increased in
grouped larvae until the fourth instar and dropped in the fifth and sixth instars.
Alternatively, in solitary larvae this efficiency was significantly lower in the
first to fifth instars relative to the grouped-reared larvae. Finally, development
was significantly higher in the isolated sixth instar larvae as compared to
grouped larvae (Kirichenko and Baranchikov, 2004). This information
suggests that the effect of density correlates with accelerated development of
the SSM at early stages of their life cycle (first to third instars) when the larvae
are more vulnerable. However, the development of later instar larvae (i.e.,
fourth to sixth instar) is faster when the larvae grow in isolated conditions,
possibly due to reduced competition for food resources (Kirichenko and
Baranchikov, 2004).
2-28 Dendrolimus Pine Moths 12/2012-01