You HAVE to see this! :)
http://www.so-sweet.cwc.net/Films/alien_2_sulla_terra.htm
The IMDB listing. (http://us.imdb.com/Title?0078749) Funny thing is, I thought this and "(Alien) Contamination" were the same film until right now. They seem to have identical plots.
There even seems to be some confusion in the "comments" section for Andrew's "Alien Contamination" review (under the retitle "Toxic Spawn"). Weird.
I remember this thing.
....Chest (And head) bursting, caves, a depopulated boweling alley...yeah, thats the one....