There Is No Queen
The toxins pest control has used penetrated the hive in the lower portion. They have killed the queen and a lot of other bees. The hive cannot live without the queen so it was in danger. At this point, it looked like David would not be able to help the bees.
It was no easy task seeing thousands of bees affected by the poison. He wanted to try and help the rest of them even more and try to find them a new queen. It is a complicated and risky process. He must do it.