I remember that back in the 1980s, 1980-1984, gypsy moths were a veritable plague in the Northeast United States. They were literally everywhere. Sidewalks were covered with their squashed bodies (of the caterpillar). You would drive through areas and every single tree would have dozens of nests. Every summer would be gypsy-moth-a-geddon.
By the late 1980s this completely ended for some reason. I sometimes see a gypsy moth caterpillar here or there, but it is a rarity.
What happened? Did a predator proliferate? Was there a pathogen or disease that wiped them out?