Milk: It does a body good

As you try to figure out a way to deal with the humans, a woman walks by, cradling a baby in her arms, breastfeeding it.

Wait... Breastfeeding! Of course! Suddenly, you realize that it will be much easier for succubi to corrupt humans compared to incubi for one simple reason: Breastmilk.

Breasts have long been a weakness of human males, and now they will be their downfall.

All you need for this plan to work is milk. Once you get enough milk, it'll be easy to corrupt humans: Milk is the second-most common drink on the planet, only behind water, and it's much easier for a succubus to contaminate water than it is for an incubus!

Only one question remains...