Monoculture leads to even further harms to the biological world. Insects are important elements to functioning ecosystems. The presence of certain insects enhances crop production, because they either pollinate flowers without which fruit would not form, or they are predators of other insects that might otherwise eat and destroy the food crop sought. Insects are both “bad” and “good” for agriculture, but without the presence of the “good” ones, the “bad” ones take off in population and thus cause much more damage to crops. The key to functional agriculture is a healthy balance in the insect ecology.
The industrial model of food production of course finds good and bad commingling to be too complicated to deal with. Easier, it seems, is to just “spray ‘em all and let god sort ‘em out”. Pesticides (insecticides, herbicides, and fungicides) are widely used in agriculture. As with the fertilizer issue, commercial agriculture often overuses pesticides to guarantee a good-looking salable product—so even if a particular pest won’t destroy a broccoli head, but might make it look less perfect, the agricultural operation is more likely to opt for pesticides than to risk having a product that won’t sell.
Using these chemicals isn’t very precise.  We kill our targets, but also the other insects around. This causes additional problems we then need to solve, two of which have received increasing media attention. These are the problems of pesticide-resistant insects, and the worrying loss of pollinators.
insects are known to develop resistance to the very chemical pesticides designed to kill them. That bugs develop immunities and resistance to these chemicals should come as no surprise to entomologists: because insects have a short lifespan and reproduce quickly, they can evolve relatively quickly (compared with mammals whose gestation and generational periods are relatively longer). They pass on traits and are selected to reproduce those traits that succeeded (like pesticide resistance) very quickly. 
So, what do farmers do when they face insect “superbugs” (and “superweeds”, the plant equivalent)? They are forced to buy ever more, and newer versions, of the agrochemicals that caused the development of the “supers” in the first place. This is part of what critics refer to as the “pesticide treadmill” that many farmers get stuck on.
The loss of pollinators—in particular, the European Honeybee that is responsible for pollinating every major crop type in the United States—has gotten so bad that even mainstream cereal companies are running campaigns to raise awareness of the issue and find a solution. Why are people so worried? “Colony Collapse Disorder” became a “thing”, when beekeepers, researchers, and farmers all noticed a sudden and precipitous drop in bee populations, largely when entire colonies would be found dead or disappeared.
Research has traced these collapses in part to the increasing use of “neonicotonoids” , a particularly virulent class of pesticide because they are “systemic”, meaning they are taken up into all parts of the plant sprayed with them. This means toxic pollen and nectar, which bees in particular can take back to their hives. Many pesticides like “neonics” don’t kill bees outright, but impair them as individuals and as hives.
With the drop in bee populations, and a similar decimation of native pollinators, fruit and vegetable production suffers yield reduction. The monocultures of European honeybees that are used by commercial beekeepers to pollinate monoculture orchards are in decline , and some crops are beginning to suffer in production, yet commercial beekeepers and industrial farming groups continue to fight the regulation of pesticides like neonicotonoids.
If large monocultures lead to the need for agrochemicals, and those chemicals cause problems for insects we rely on (not to mention those we don’t , and many other animals and living things that are harmed by the chemicals), and create only further problems for agriculture, a solution will not come from a new, smarter chemical or system of chemical use. It will emerge from a form of production that avoids and minimizes the use of chemicals in the first place.
 Fun fact: modern pesticides were originally developed from the weaponized gasses that countries used to kill enemies in World War II; nitrogen fertilizers were developed by the same plants that made nitrogen-based bombs! “Before it made it onto farm fields in a big way, Haber’s breakthrough fueled the US and European munitions industry, particularly in World War II. In that way, the industrialization of farming shares roots with the industrialization of killing represented by modern war.”
 Though not as quickly as bacteria—which are evolving their own resistance to the antibiotics used in industrial animal agriculture! In fact, many forms of life develop resistance to various “xenobiotics”, like herbicides, fungicides, and rodenticides.
 I say “in part”, because nutritional stress, habitat loss, and other pests, pathogens and pesticides also play roles in colony collapse.
 Seems unwise to expect healthy outcomes, even setting aside pesticides, when these bees are fed corn syrup to survive winters to supplement their monoculture diet of peaches, almonds, cucumbers, or whatever flower nectar they consume for weeks on end.
 Some economically less important—but no less important in other ways—pollinators, like the Monarch butterfly, have also been endangered by agrochemicals, whether pesticides or herbicides. Unlike the bee issue, monarchs are not only threatened by their individual exposure to harmful chemicals. Instead, scientists have pointed to the loss of the main food sources for monarchs in their lifecycle development: the milkweed. Milkweed is a typical weed across agricultural landscapes in the U.S. Increased use of herbicides to rid fields and roadsides of milkweed has drastically reduced the available habitat and food for migrating monarchs.