Gary sprays his sugarcane field with a highly effective pesticide called “Bug X 4.0.” For five years, the pesticide works well, effectively killing almost all the weevils trying to eat Farmer Gary’s crop. However, during the 6th year, some of the crop takes a hit. During the 7th year, he loses half of his crop, and during the 8th year, he loses almost the entire cane field to weevils, despite using twice the usual dose of Bug X 4.0. What happened?