Hear the words “aphid killers”, and the first bugs we think of are ladybird, or perhaps, lacewing larva. Others may have heard of the parasitoid wasps that lay their eggs within aphids, where they will hatch to kill the aphid from the inside. But there is also a sub-family of wasps, the Pemphredoninae, that specialize in hunting aphids.
These small wasps are in the genus Passaloecus (Hymenoptera, Family Crabronidae), and were found absorbed amoung the blossoms of our lilac tree. Aphid wasps nest in holes that may have originally been left by wood-boring beetles. Passaloecus wasps then stock cells within the tunnel with aphids and lay an egg on or near them, for the emerging wasp grub to feed on. Some Passaloecus are also raiders, stealing the stashed aphids of other Passaloecus species¹.
See Eric R. Eaton’s post for more
And thanks to Dr. Matthias Buck of the Royal Alberta Museum for the ID.
¹Aphid-hunting wasps: a field study of Passaloecus. Sarah A. Corbet and M. Backhouse. Article first published online: 24 APR 2009 (DOI: 10.1111/j.1365-2311.1975.tb00549.x) The Royal Entomological Society 1975.