Aphids

• Leaf cupping or curling, particularly after a key lime tree's first flush of growth, are symptomatic of aphid infestation. Other symptoms include sticky and distorted or curled leaves. The Arizona Cooperative Extension recommends using a water hose to physically remove the tiny insects, or you can spray the tree with a mild soap solution.
  
  

Asian Citrus Psyllid

• Treat the Asian citrus psyllid, or leafminer, with a soap solution or water spray, according to the Arizona Cooperative Extension. The leafminer attacks a lime tree's new growth, leaving behind curled or cupped leaves, leaf distortion and a waxy filament. Use a citrus spray oil on larger infestations, but tree damage is minimal in most cases, and therefore does not require the attention of the home gardener.
  
  

Thrips

• Thrips, small, flea-like insects, cause leaf distortion and cupping, as well as yellow, white or silver-colored streaks on the leaves. Thrips do not need control, as the damage is only cosmetic.