A brief excerpt about the tiphiid wasps from a linked article:
These two tiphiid wasps are among several natural enemies imported for the biological control ofJapanese beetle. Tiphia popilliavora is native to Japan, where it attacks the larvae of the Japanese beetle (Popillia japonica), as well as to Korea and North China. In its native areas of Korea and North China, T. vernalis is parasitic mainly on scarab species in the genus Popillia other than Japanese beetle. T. popilliavora was the first of the imported parasites to be released. Fewer than 100 adult wasps from Japan were first released in New Jersey in 1921-22, but they quickly established and their progeny and strains from Korea and China were distributed over the infested areas of 10 states by the end of 1950.
... T. vernalis was first released in New Jersey in 1925, and by 1953 over 2,000 colonies of this species were distributed over 15 states.
...The adults are 1/4" long shiny black wasps. The adults of T. vernalis emerge during May and early June and feed on aphid honeydew.
...The biology of T. popilliavora is similar to T. vernalis, but the adults emerge in August and early September and feed on nectar from the blossoms of umbelliferous plants, especially wild carrot, rather than honeydew.
...Under favorable conditions, T. vernalis can parasitize up to 60% of beetle larvae in an area and T. popilliavora somewhat less. The abundance of both species is greatly influenced by the availability of adult food sources. The females feed in the morning and then fly relatively short distances to deposit their eggs. This is why parasitism by both species tends to be greatest in grassy areas near weedy borders that contain aphids or wild carrot.
...I'm cautiously optimistic that my garden conditions could match the "favorable conditions" mentioned in the article. I get aphids-a-plenty in spring, and for the fall Tiphia, I have (not wild but) regular carrots blooming right now, and as luck would have it, I have been deadheading them since I'm not interested in saving carrot seeds this year since Certain *someone* gave me a HUGE stash of seeds.
This has meant that they have been continuing to bloom. Also have celery and other umbelliferous bloomers that are blooming now and will be blooming later.
One concern I do have is that I had the impression that Japanese beetles came late this year. That may mean the T. vernalis missed them altogether, and the T.popilliavora may not find the 3rd instar grubs they are looking for.
...on the other hand, I did recently see several severed JB heads on leaves of plats under the beans (a squash leaf in this case) I thought birds or praying mantis, but maybe it was T. vernalis larva at work.
ETA -- ah. I have it wrong. The wasps actually sting the grubs in the soil.
https://www.hort.uconn.edu/ipm/turf/htms ... Tiphia.pdf
https://ipm.uconn.edu/documents/raw2/The ... hp?aid=167
After mating, female wasps burrow into the soil and search for grubs.
This one has photos and descriptions that I recognize, so I think I do have the spring Tiphia in my Garden/Ground Patrol