All these try to get on my pellies,and other plants in greenhouse,,ok,maybe not purple ones,,but them first ones..grrrr.
They love uniques,scented , regals,and zonartics,not so much zonal pelargoniums,,but if nowhere to go they get on them too. Especially when plants are in stress,,to dry,to wet or to much sun and it is to hot.
Last year i had whitefly invasion in old tunnel,and got some in new too.I tried everything yellow sticky paper,contact pesticides( that stench .brrrr),systemic ones .I bought encarsia wasp eggs,who is natural predator of whitefly,they didn't hatch...So last winter i decided that is all i must find something else,something what is natural,do not stink ,do not do damage to our health,to other insects .I think i found it,,it is neem oil,,you can get it at health stores,cost less them systemic insecticides ,do not do harm to you or other around,,except white fly ,green fly,to all who love to suck sap from plants,,or even eat them.
I started to spray plants every 7 days,,i do it on Mondays,,on one liter warm water you take 5 mll neem seed oil,,add little kitchen soap,i using Ecover Washing-Up Liquid ,because oil won't dissolve in pure water as you know.And then just go and spray plants and try to wet underside of leaves,where whitefly loves to hide.This liquid you must use in 8 hour time.How do its work,,read here
And as i can see it really work,,i have white and green fly still in,but it is not in damaging numbers,,they just come on plants what i forgot to water or over water,,sometimes happen,but my scented and uniques are clean,same as all other.
Hope this info will help you,if so let me know.
p.s. forgot to tell,best time to spray plants is early morning or afternoon.Sun can damage foliage on your plants.