The original idea isn’t mine, it came from USDA studies about different types of tropical guavas in Vietnam. They noticed that when citrus orchards are intercropped with guavas, the citrus orchards are more long lasting even if the HLB disease pressure is high.
https://naldc.nal.usda.gov/download/33248/PDF
So I am extending this to a general theory that based on the Myrtaceae family of plants that are known for their many bioactive compounds, it has insecticidal properties against the Asian Citrus Psyllids and other insects. The Melaleuca tea tree belong to the Myrtaceae family and has also excellent antimicrobial properties and the oil was used as antiseptics by the Australians during WW II.
So I looked around for Myrtaceae that are fruit bearing and able to survive the cold in our area. Feijoas or Pineapple Guavas and the Cherry of the Rio Grande are excellent fruiting trees for such if tropical guavas can’t be grown. Crepe Myrtle, a non-fruiting tree, would be good. So I started planting these in my yard in close proximity to my citruses. Even though we don’t have the ACP or the HLB yet, at least my yard won’t be the preferable one to be visited by this citrus plague from hell. I could have grown the Melaleuca tree but they die out in our soil. So if you can grow Tea Tree, it would even be better. I also have tropical guavas, but they’re tucked in under the eaves of our south facing wall, protected from frosts and cold air flow or drainage.
So keep these in mind when you are growing citruses.
Asian CItrus Pysllids are attracted to young citrus shoots and trees already infected with HLB. They are repelled by sulfur compounds in guavas such as the dimethyl disulfide, and also extracts from chives, garlic, onions… of the Alliaceae family.
Here’s some more scinetific literature:
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1744-7917.2009.01271.x