As the number of insect species declined due to spraying, the blueberry production decreased. explain how these two events might be related even though the pesticides did not land directly on the blueberry plants

There are several mechanisms that might explain this result. The key fact is that insect species vary with respect to whether they are beneficial or detrimental to blueberry plants. If the species which experienced decline were directly beneficial to blueberry production, by aiding pollination for example, then their decline would hamper blueberry production. It could also be the case that detrimental species were not affected, or that detrimental species flourished because predators or rivals were eliminated.