Health Canada is advising Canadians to not use malathion products older than one year due to chemical changes in the product over time. Malathion kills insects by preventing their nervous system from working properly. Malathion is effective in killing mosquitoes, aphids, loopers, moths, beetles, leaf bugs and other pests. Alarmingly, when stored at elevated temperatures over time a toxic chemical called isomalathion can naturally form in malathion products. Isomalathion is significantly more toxic to humans than malathion. Make sure any products containing malathion are stored in a cool (between 20-23°C), dry, well ventilated place for no longer than one year. If you need to dispose of this insecticide, contact your local municipality for information. Health Canada allows the use of malathion products which are older than one year when all of the following are met: an accredited laboratory test results show that the malathion remains within accepted standards, the test results are maintained for compliance verification purposes, and the product continues to be used in accordance with the other label directions.
https://www.linkedin.com/pulse/use-caution-before-using-insecticide-malathion-randy-bilesky?published=t