Hi John, 

You have photographed a type of tent-making caterpillar colony. It is not a pupa, but a large silken mass inhabited by a large population of caterpillars. It is difficult to identify them to species without seeing the caterpillars themselves, but most tent-making caterpillar species are controlled in the same way. 

Often, there is no need to control these insects. Control is warranted when there are sustained, high levels of defoliation over several years. But trees often tolerate the damage and bounce back quickly after. If it's easily accessible and not on a major limb, the mass can be pruned out. 

There are many natural enemies that prey upon these caterpillars. This includes birds, predaceous insects, parasitic wasps and flies, and entomopathogenic viruses. These organisms are naturally occurring, but you can encourage their populations through conservation biocontrol. 

The microbial insecticide Bacillus thuringiensis (Trade Name: Dipel or Thuricide) is an entomopathogenic bacteria that is effective and selective for the control of all tent-making caterpillars. Several contact insecticides also are effective for tent-making caterpillars, such as carbaryl (Trade Name: Sevin), pyrethroids (e.g. permethrin, cyfluthrin, esfenvalerate). Spinosad is a naturally derived product which is also effective against these caterpillars, but it is usually only available to commercial applicators. When applying any of these insecticides (including Bacillus thuringiensis), make sure to follow the instructions on the label meticulously. Let me know if you have further questions. 

https://extension.colostate.edu/topic-areas/insects/tent-making-caterpillars-5-583/