a desert shrub
Questions 44 through 46. Listen to a talk in a biology class.
This morning I want to tell you about a recent scientific discovery dealing with the relationships between plants and animals. This is about a desert shrub whose leaves can shoot up a stream of poisonous resin a distance of six feet. Do you think it would be safe from all attacks by insects? But a recent study has found one insect, a beetle that can chew its way past the plant’s defense system by cutting the main vein that delivers the poison to the leaves . This vein cutting is just one method the beetles used to prepare a safe meal. Another is by cutting a path all the way across the leave to hold the flow of chemicals. Then they simply eat between the veins of poison. In the past , scientists who studied insect adaptation to plant defenses have focused on chemical responses. That is, how the insects can neutralize or alter the poisonous substances plants produce. What’s unique about this chewing strategy is that the beetle is actually exhibiting a behavioral response to the plant’s defenses rather than the more common chemical response. It is only after a beetle’s survived several encounters with the plant’s resin that it learns how to avoid the poison: by chewing through the resin transporting veins on the next leaf it eats. And thus gives itself a safe meal. However, it can take a beetle an hour and a half of careful vein cutting to prepare a small leaf that takes it only a few minutes to eat. So, though the method is effective it’s not very efficient.