What loisonous alkaloid is extracted from tobacco leaves and used in insecticide?

The poisonous alkaloid extracted from tobacco leaves and used as an insecticide is nicotine. It acts as a neurotoxin to insects, disrupting their nervous systems and leading to paralysis or death. Due to its toxicity, nicotine-based insecticides must be used with caution to avoid harm to non-target organisms, including humans and beneficial insects.