- Caffeine is found in varying quantities in the beans, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants.
Wanting to find out more, I looked up the reference provided. In an experiment with tobacco hornworm (Manduca sexta) larvae, the researcher reported, "In concentrations from 0.3 to 10 percent (by weight) for coffee and from 0.1 to 3 percent for tea, there was a dose-dependent inhibition of feeding associated with hyperactivity, tremors, and stunted growth. At concentrations greater than 10 percent for coffee or 3 percent for tea larvae were killed within 24 hours."
He also reported, "Dried tea leaves, which contain two to three times the caffeine of dried coffee beans, were about two to three times as effective as coffee beans in inhibiting weight gain. Furthermore, the concentrations of caffeine found naturally in undried tea leaves (0.68 to 2.1 percent) or coffee beans (0.8 to 1.8 percent) were sufficient to kill most Manduca larvae, suggesting that naturally occurring methylxanthines [of which caffeine is one] could function as endogenous insecticides. When applied as a spray to natural feeding substrates such as tomato leaves, caffeine [...] exerted pestistatic and pesticidal effects that resulted in leaf protection."
I rarely drink coffee or tea, so can't identify with many of my friends who need a cup of coffee to kick-start their day. The brew smells heavenly but is way too bitter for me -- I tend to dilute it heavily with lots of milk and sugar! I mostly only drink it at department meetings or seminars where coffee & tea are served...