This insect has been on our lime tree for 3 months and we sprayed some insect killer bought in a local store for general insects. We had some results for a little while but they’re slowly coming back. You can see the insect in the picture very well. Also, the leaves have black spots that look horrible. I hope this insect is a good one and we don’t need to exterminate it. Thanks a lot!
Your critter looks like the nymph or young stage of the Milkweed assassin bug. The angle does not show the mouthparts, but it should have a “beak” on the underside of the head. This beak is for sucking the fluids out of prey. The little black specks on the legs must be litter of some sort…tho it if they are part of the insect we would need a clearer and closer photo.
The assassin bugs are predators, so they feed on other insects and worms. This is called the milkweed assassin bug as it looks like milkweed bugs. If it has been on your lime tree for several months, then perhaps you have another pest on your plant that is causing the black spots…and the assassin bug is eating the pest. What other critters have you seen on your plant?
It could very easily be that the black spots are caused by a disease. The assassin bugs are just keeping insect pests off of your lime. If you have a closeup photo of the leaves that might help.
In either case it would be best not to spray the lime with any insecticide as you will kill your helpers. Should you find another critter on the lime get a photo and perhaps we could help if control of something is needed.
Enjoy those limes…we northerners are jealous!