We want to Kill harmful insects to humans and animals without the use of pesticides that pollute the environment: such as flies, Periplaneta americanc, Melanoplus mexicanus, and ant.
You can use natural products such as Neem to kill insect with no synthetic pesticides.
From experience Sometime you may use fine dust (for example Dichotomous Earth - DE) to suffocate insects in grains storage with no synthetic pesticides
To decrease the insect population ,you can depend partially on natural factors such as temperature ,humidity ,rain .These can in some cases intentional factors such solarization. The use of mechanical and physical factors will reduce insect populations .Agricultural practices are very useful such as pruning,agricultural rotation etc..Resistant cultivars and genetic engineering are also useful.Natural and artificial such as predators and parasitoids are important.The use of non toxic chemicals are also useful .