A "systemic" insecticide is a chemical that is absorbed by the plants, so that any sucking insect that tries to chomp on it gets poisoned and dies. The usually last a few months I believe, but you have to be careful how much you use and some orchids might not react well to a specific insecticide, so it pays to research a bit.
As for Canadian availability, I gave up on finding equivalents here some time ago myself and I just ordered them from the US through eBay. Be aware that any chemical has a chance of being rejected at the border though
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But I could never find Physan 20 in hydroponics stores here or any form of imidacloprid (a systemic) so I took a chance got my products (if you try, also be careful to watch how much they charge for shipping too!). I did see Malathion in garden centers and hardware stores though.
Hoping for someone to pop in with some Canadian sources too
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