nature is amazing without doubt..as for opium being a poisonous alkaloid to insects, not so sure opium has any effect on insects.
There are insects that attack opium poppies, for sure. Just like the Monarch butterfly that has evolved to be able to eat poisonous milkweed, no doubt some insects have evolved to be able to eat opium poppy plants.
That doesn't obviate the origins of opium, however. It rather affirms evolutionary theory, since animals have evolved to be able to ingest this poison.
An interesting note here: The Monarch butterfly's caterpillars, through eating the milkweed plant become very bitter tasting to birds. A young bird will try to eat one of these, then gag violently. It will never even touch that caterpillar again. So, evolving a tolerance for the alkaloids in milkweed also turns out to protect these caterpillars from predation. The effect continues on to the adult.
Here's another interesting note: Another butterfly looks very similar to the Monarch. It is also avoided by predatory birds, even though it doesn't ever ingest the milkweed.
Again, evolution is an amazing thing.