Leaf loss during flower?

[onewarmguy]

Hi all, The girls are into their fourth week of flower and I'm starting to get some leaves turning yellow. The leaves are at the bottom of the plant and aren't getting a lot of light due to the bushiness of the leaves above. I can't remember for sure but I seem to recall reading something here about this being a natural part of the flower stage as most of the plants energy is going into producing buds. Can anybody confirm or deny? Or am I looking at a pest?

 

[onewarmguy]

 

[Phytoplankton]

I wouldn't worry, during flowering the lower leaves will yellow and fall, I trim them off and get the waste out of my greenhouse to cut down on the possibility of mold. Doesn't look like it's caused by pests.