Hello. You did not enter the text to which this question refers, which makes it impossible for it to be answered. However, I will try and help as best I can.
The only way you can answer this question is by reading the text. During this reading, you will notice that there is an element in monoculture that is harming bees, making them have a very difficult life or even die. This element is what is affecting the bees. The author will show why this element is harmful to bees through sentences that prove the effect that this element promotes and how it only exists in monocultures. These sentences will be the text evidence.
It is likely that the author shows how monoculture requires a large use of pesticides, which ends up harming the life of bees. He can also show that monoculture decreases the availability of food for bees, since all monoculture plants only flower once a year and leave the bees without food for the rest of the year, as there is no plant diversity in the monoculture.
