If bears find insects after they move decaying logs, they more frequently move decaying logs. This most clearly indicates that finding insects is a

Reinforcement

Explanation:

Reinforcement can be referred to as anything that can be used to increase, enhance or strengthen a desirable behavior in a person or an organism. Reinforcement is of two types, they include positive reinforcement and negative reinforcement. Positive reinforcement has to do with adding a reward in order to enhance a desirable behavior, while negative reinforcement has to do with removing an undesirable thing in order to strengthen a desirable behavior.

From the question asked,  because the presence of insects after moving the decaying logs increased the frequency at which the bears moved the decaying logs, the finding of the insects is, therefore, a reinforcement. The finding of the enhanced or strengthened the desirable behavior.