This is interesting.

if it helps
list - World Catalog of Symphyta, 2010
plants - ECatSym
...
Family MEGALODONTESIDAE

no species

Family PAMPHILIIDAE
Subfamily CEPHALCIINAE
Genus Acantholyda
Subgenus Acantholyda

apicalis (Westwood, 1874)
atripes (Cresson, 1880)
erythrocephala (Linne, 1758)
marginiventris (Cresson, 1880)
pini Rohwer, 1911
poeppigii (Zaddach, 1866)
runcinata Middlekauff, 1958
tesselata (Klug, 1808)

Subgenus Itycorsia

aequorea Middlekauff, 1958
albomarginata (Cresson, 1880)
angulata (MacGillivray, 1912)
atrata (Cresson, 1880)
aurigera Middlekauff, 1958
balanata (MacGillivray, 1923)
bicolorata (Norton, 1869)
brunnicans (Norton, 1864)
brunniceps (Cresson, 1880)
bucephala (Cresson, 1880)
burkei Middlekauff, 1958
chicoutimiensis (Huart, 1879)
circumcincta (Klug, 1808)
crocina Middlekauff, 1958
depressa Middlekauff, 1958
floridana Greenbaum, 1975
luteomaculata (Cresson, 1880)
maculiventris (Norton, 1869)
nigripes (Cresson, 1880)
nigrita (Cresson, 1880)
ochrocera (Norton, 1869)
ruficeps (Harrington, 1893)
terminalis (Cresson, 1880)
verticalis (Cresson, 1880)
zappei (Rohwer, 1920)

Acantholyda species not assigned to a subgenus

thalictra Middlekauff, 1958

Genus Cephalcia

californica Middlekauff, 1958
distincta (MacGillivray, 1912)
fascipennis (Cresson, 1880)
frontalis (Westwood, 1874)
fulviceps (Rohwer, 1910)
hopkinsi (Rohwer, 1910)
marginata Middlekauff, 1953
nigra Middlekauff, 1958
provancheri (Huart, 1879)
semidea (Cresson, 1880)

Subfamily PAMPHILIINAE
Genus Neurotoma

crataegi Middlekauff, 1940 - Canada, USA - ?Crataegus
edwardi Liston, 1996 - Canada, USA - ?Padus, ?Prunus
inconspicua (Norton, 1869) - Canada, USA - Prunus
nigra Middlekauff, 1988 - USA - ??
willi Middlekauff, 1958 - USA - ?Crataegus

Genus Onycholyda

amplecta (Fabricius, 1804) - USA - Rubus
excavata (Norton, 1869) - Canada, USA - Cornus
luteicornis (Norton, 1869) - Canada, USA - Rubus
multisignata (Norton, 1864) - Canada, USA - ??
nigritibialis (Rohwer, 1912) - Canada, USA - ??
quebecensis (Provancher, 1878) - Canada, USA - ??
rufofasciata (Norton, 1869) - Canada, USA - ?Dasiphora
sitkensis (Kincaid, 1900) - Canada, USA - ?Rubus

Genus Pamphilius

burquei (Provancher, 1878) - Canada, USA - ??
cinctus Harrington, 1893 - Canada, USA - ??
infuscatus Middlekauff, 1964 - Canada, USA - Populus
middlekauffi Shinohara & D.R. Smith, 1983 - Canada, USA - Cornus, Corylus
ochreipes (Cresson, 1880) - Canada, USA - Viburnum
ocreatus (Say, 1836) - Canada, USA - ??
pacificus (Norton, 1869) - Canada, USA - Rosa
palachei (Ashmead, 1902) - USA - ??
pallimacula (Norton, 1869) - Canada, USA - ?Rosa
persicum MacGillivray, 1907 - Canada, USA - Padus, Persica
phyllisae Middlekauff, 1964 - Canada, USA - ?Quercus
pullatus (Cresson, 1880) - Canada, USA - ?Viburnum
rileyi (Cresson, 1880) - USA (Connecticut to West Virginia, west to Michigan, Iowa, Missouri ) - ?Amelanchier
semicinctus (Norton, 1862) - Canada, USA ( Quebec to North Carolina west to Tennessee and Indiana) - Amelanchier, ?Malus, ?Prunus
uniunguis Middlekauff, 1964 - Canada, USA - ??
vernalis Middlekauff, 1964 - Canada, USA - ??

Unplaced Pamphilius

canadensis Norton, 1869 valid is Lyda canadensis Norton, 1869 - Nearctic region - ??
scripta Say, 1824 valid is Tarpa scripta Say, 1824 - Nearctic region - ??

...
? - non-valuated or questionable
?? - unknown

...
Please let me know if you have additional information.

I do not have more information at present (except that Acantholyda erythrocephala feeds on Pinus spp.), but I copied your list here so it will be easy to find again!

(I did not check coniferous species)

Some BugGuide editors don't like having the website cluttered with photos of plants, so they remove them after the plant has been identified. I assume that's what happened in this case.

It is subfamily Pamphiliinae because the depression (dented area) in the middle of the anal segment is not triangular. Triangular dent in subfamily Cephalciinae (Acantholyda and Cephalcia).
But, unfortunately, I could not find any species associated with these plants.