Insecticide application over time

Insects, fungi, viruses, rodents, and weeds that eat or compete with our crops have taken advantage of the ways we cluster food plants into agricultural fields
Pest = any organism that damages valuable crops
Bigger problem in monoculture
Weed = any plant that competes with crops

Pesticides = poisons that target pest organisms
Insecticides = target insects
Herbicides = target plants
Fungicides = target fungi
91% of pesticide sales are for agricultural purposes
85% of pesticides sold in Canada are herbidices

Usefulness tends to decline with time as pests evolve resistance to pesticides
Small fraction of insects and microbes have genes that confer some degree of immunity to a given pesticide
If an insect survives pesticide, resistance is passed through their genes to insect offspring
Evolutionary arms race: chemists increase chemical toxicity to compete with resistant pests