Dagame:

Nephila pilipes  spiders prey items include flies, beetles, locusts, wood moths and cicadas. Sometimes their strong webs manage to trap small birds or bats, and the spider will wrap them and feed upon them.  There is a paper by Tso et.al. 2005 called "Giant wood spider Nephila pilipes alters silk protein in response to prey variation" in this link which can answer your question.

http://jeb.biologists.org/content/208/6/1053

Regards,

Luis Miguel

If you mean actual preference I do not think anyone has done real preference studies on Nephila spp. In terms of what they will eat they seem to eat almost anything that they can catch except they do sometimes cut Hymenoptera out of the web.

Nephila are quite omnivorous, especially when getting adult and large. They feed on various insects

While very small Nephila (and other web builders) may ingest some plant (and other) material when they ingest their webs before rebuilding, and a few spiders will drink flower nectar, their are no truly omnivorous spiders.  Instead we call most spiders that eat a wide variety of prey "generalist predators" and this is true of all Nephila I am aware of.  One article (see link to RG) studies feeding behavior in an African species and a very old article reports on a study in Costa Rica (some think this article has poor information) but both in general show the two different species are generalist predators feeding on any appropriate (size and lack of toxicity) animal prey venturing into their webs.

Data Notes on Feeding Habits of Spider Nephila sp in an Acacia Wo...