Usually for aphids chemicals aren't needed most of the time if it's not a bad attack. Soap, rubbing alcohol and manual removal usually do the trick. Systemic stuff is a bit of overkill just for aphids, and it's usually recommended to treat aphids on fruit trees for example, because there is no other way of getting to them.
As for the aphid being different from what you're used to, there are hundreds of different species, some of them preferring one type of plant more than another.
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Camille
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