The larvae hatch shortly thereafter and begin feeding on the previous year's needles. Within a month, they have completed larval growth and left the branches to pupate. They spin a whitish, oval cocoon about themselves in the litter or understory. Normally in Vermont, we are dealing with a single generation per year. The eggs and young larvae are susceptible to extremely low or even rapidly fluctuating temperatures.
Heavy rainfall is also detrimental.
Birds, and probably rodents, prey on the cocoons. In Wisconsin, three parasitic wasps have been reported as important natural controls. In North Carolina, the mass rearing and releasing of M. dentipes achieved adequate suppression of IPS outbreaks. E. amictorius is a parasite of the ultimate-stage larva, and the other two are cocoon parasitoids. Finding the cocoons and destroying them is very difficult and generally ineffective.