It’s bad news for butterflies and moths but good news for parasitoids. Parasitoids do not die out in the winter, no more than the butterflies and moths that are their hosts.
Tachinid flies spend the winter as first instar maggots in their hosts or as pupae inside hosts or in leaves and soil.
Braconid wasps spend the winter as larvae.
Ichneumon wasps over winter as adults.
There are many other types of parasitoids, creatures that lay eggs in, on, or near caterpillars. The wasp larva enters the caterpillar and eats it from the inside out. Some emerge from the butterfly caterpillar and some emerge from the butterfly chrysalis. Their numbers thin during the winter, just as butterfly numbers dwindle in the winter. In the spring, both parasitoids and butterfly numbers increase with each generation.
They are a fact of life, playing an important part in the preservation of butterfly and moth species as a whole, even as they kill thousands of caterpillars and chrysalises each year.
Most of us understand their importance in nature but we sing the same refrain. “You will NOT live in MY yard if I can help it!”