Insecticide formulations having improved chemical and physical stability and related methods are disclosed. The insecticide formulations may include a plurality of microcapsules, each including at least one organophosphate insecticide (e.g., chlorpyrifos-methyl) at least partially surrounded by a polymer shell. The insecticide formulations may be used to control insect populations by singular or periodic applications. The microcapsule polymer shell of the insecticide formulations may be formed by combining a cross-linking amine and a hydrophobic monomer (e.g., an isocyanate) at a molar ratio of amine to isocyanate groups of less than about 1:1.
