Steve
If you're growing Pings well they won't need hewlp with feed.
Generally Pings catch all they need in the form of Gnats or similarly
sized flies. If your plants are looking sickly, feeding them might
actually push them over the edge!
On the other hand, if you really feel the necessity to feed and if
you're sadistic in your private life (we'd all like to know more), then
you can feed Pings any fly that isn't big enough to crawl off (e.g.
house flies or bluebottle are too strong and generally struggle free).
Of course you can stun the large flies first but this is an art
(difficulty akin to any martial art) where you have to stun the fly
sufficiently to prevent them recoving before digestion has progressed,
as opposed to splattering the fly (in which case too much nutrient is
lost to make it a worthwhile food).
In extremis, you can use quarter (or weaker) strength foliar feed about
monthly during the growing season.
Regards
Paul