The regular weight allows some heat buildup and can be used as season extenders in the Spring and Fall. The super light cover is used for an insect barrier in the Summer. For crops requiring pollination, the covers must be removed when flowering starts. Hand picking and destroying the pests is an effective method. I have had good success controlling potato bugs by shaking the plants into a lined basket or box.
Potato bugs fall off easily into the box.
Also, a butterfly net comes in handy. I use it to capture flea beetles on eggplants and the white cabbage worm butterflies fluttering around, looking for a cabbage family plant to lay its eggs on. Trap slugs in a shallow dish containing beer. Commercially available slug traps are also available. Sticky red spheres hung in apple trees help trap apple maggot flies.