You will get more hits if you google for 'psyllids' instead of 'psylla'
If thinking of spraying, pyrethrum is relatively low toxicity and acceptable
by most organic standards if extracted from plants. How this is OK but the
same compounds made in a vat are not acceptable beats me but that's organic
standards for you.
Note that it is still an insecticide so you should be careful not to spray
beneficial insects such as bees.
spray 2x year around April/August when infestations are at peak with
your product of choice.
If you are unfamiliar with some of the control products here is a
Dig into info listed below for various products and further reference
leads. Viable Control products/methods are sometimes buried deep in
David is correct re: Psylla & Psyllid but also try googling Citrus
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