1/3 of crop to pests?

I was watching a program about bees dying off and there were folks talking about how really bad monocultures are and how having a farm without chemicals and having wide variety of stuff growing instead of monoculture about 1/3 of crop is lost to pests.
I'm paraphrasing here but that is the gist of what some were saying.
I know some organic experts here have all matter of pests under complete control but for the rest of us I was thinking this sounds about right and to plant twice as much as you m might want to grow because there will be some loss.
this reminded me---now is time to order seeds for spring and summer.

I have great sympathy and respect for those who do it without chemicals. I was really questioning my permaculture methods a few years ago. Others knew well before me that growing landrace seeds is a can’t miss. It just takes more time than people are willing to give it. As you said, monocultures are a big problem and convincing folks to change is difficult. I’m reminded of a story about Masanobu Fukuoka. He would loose a small amount of his rice crop to aphids. He considered this a beneficial form of pruning as they always attacked the weakest plants. Aphid predators were there to take care of the problem and life returned to normal.
I hadn’t seen an aphid here in years until last summer. They were all over my poly culture of corn, marigolds, tomatoes and cowpeas. I started seeing paper wasp, ladybugs, and yellow jackets all over the garden. I couldn’t figure out where the yellow jackets were coming from. As I walked around looking I realized I was standing directly on top of the nest! They didn’t even notice. Once the aphids were gone they packed up and left. Probably onto their next feast.