Oh man there is some bad advice here....
This to me looks like the green peach aphid, check it out here.
http://ipm.ucanr.edu/PMG/r604300111.html
Root aphids generally
do not feed on the foliage unless the infestation is really bad, and you would be seeing all kinds of issues that typically mimic nutrient deficiencies as the root system is damaged. For example rice root aphid will mimic magnesium deficiencies in high enough populations. So unless I am severely mistaken, these are garden variety aphids and are not that big of a deal. A heavy spray of insecticidal oils will deal with this issue. Botanigard will also work but, just like the insecticidal oils you must ensure good coverage of all foliage and stems and it will take about a week for the fungus to kill the insect and its eggs. A few treatments of botanigard a few days apart and this issue will be dealt with.
For the love of god don't use systemic insecticides on bud that you intend to smoke... holy fuck that is just really dumb advice. Imidacloprid is a neonicotinoid, which is generally harmless to mammals as far as I know, but ive never smoked it so I really cant tell you what putting fire to that chemical will do to you or anyone you sell that bud too. Jesus Christ. There should be a filter on this site where you upload a pic of your applicators licence before you tell someone to use an EPA restricted use chemical....
I know of no nematode species that are on the market that will parasitize aphids. Fungus gnat larvae and thrip pupa sure, but not aphids. I wouldn't waste your time or money on that avenue. They can be tank mixed with salt based fertilizers, but require moisture to live, so the idea that you will dry out your soil to the extreme to combat the aphids will just kill those nematodes you apply.
Just... just go get a insecticidal oil and spray early in the morning before the sun is full strength to avoid leaf burn and you should be all set. If you feel as though you must spray potentially harmful chemicals, or if you intend to spray in the future at all, why not go get you applicators licence and learn about the potential dangers of using these chemicals and how to best make use of them in a safe manor.