A while back I did a post on the tomato/tobacco hornworm, and just came across some interesting new research on this pest.
Caterpillar species that feed on toxic plants often have biological mechanisms to store toxic plant compounds to use as defense mechanisms. New research indicates that tobacco hornworm (Manduca sexta) has an interesting chemical defense against predators that scientists have dubbed “toxic halitosis.”
When they feed on tobacco plants, hornworms have the ability to store a small amount of nicotine in their blood (more properly called haemolymph). When threatened by predators, these caterpillars can expel the nicotine through their breathing holes (spiracles), causing the predators to retreat.
This toxic halitosis is effective at repelling many predators and also has effects against parasitoids that lay eggs inside the hornworm caterpillars. Interestingly, some predators (notably big-eyed bugs, Gecoris spp. and antlions, family Myrmeleonidae) seem to be resistant to the effects of this nicotine exhaust. The mechanism for this resistance is not yet understood.
For more on this interesting defense mechanism, check out this National Geographic article or the abstract in the PNAS.