Please refer also to the following link for details on this group:
Pemphredoninae = Link 1
Members of the subfamily Pemphredonidae construct galleries in twigs or wood, sometimes using the abandoned galleries of wood-boring insects, and store their brood cells with aphids. Other species prey on other small Homoptera. The nesting behavior of Stigmus americanus Pack. was studied by Peckham & Peckham (1895). This species a enlarges old burrows in decaying wood. Several wasps may utilize the same gallery, though they nest separately. Each well, when complete, contains about 24 dead aphids, mixed with grains of pith, and the egg is laid on the body of one of these prey.
Adults of this group make nests in twigs or in soil (Finnamore & Michener 1993). The prey is typically Aphidae (Homoptera) or Thysanoptera, but some feed also on Collembola. There were over 402 species known worldwide as of 2000.
Peckham, G. W. & E. G. Peckham. 1895. Notes on the habits of Trypoxylon rubrocintum and Trypoxylon albopilosum. Psyche 7: 303-06.