Weevils - Entomological Society of Canada

T rigonorhinu s alternatus : Valentine Ig57 :9 ; Valentine 1960 : 58, 80 ;
Valentine 797I:246.
Diagnosis. Length 2.I-3.3 mm (head excluded). Color pattern
similar to T. annulatus except elytral interstriae 3, 5, and 7 with
abundant white setae; elytral interstriae 1,2, 4, and 6 with light brown
setae and with very dark brown setae scattered in very small, numerous
spots; elytra with median spot slightly smaller and basal spot less well
defined than in T. annulqtus. Tibiae as in Z annulatus. Frons and
rostrum flattened, not transversely impressed, with surface as in
T. annulatus. Pronotum 1.2 times wider than long, widest at basal
angles; sides as in T. annulafzzs; disc as in Z annulatus, except rims of
punctures not elevated; interpuncture space of disc smooth, brightly
shining; otherwise as in Z annulatus. Elytra 1.4 times longer than wide;
sides, sculpturing, and other characters as in ? annulatus.
Distribution. Ontario to Alberta, south through the United
States to Florida in the east and Utah in the west. Alberta: Drumheller.
Manitoba: Riding Mountain National Park. Ontario: Point Pelee and
Ridgeway.
Map 6. Collection localities of Trigonorhinus ahernatue.
Comments. This is another rarely encountered species that is
known in only a few localities. Adults are similar to those of
T. annulatus, but they can be recognized most easily by the smooth
interpuncture space on the pronotum, by the color pattern, and by other
characters, as described. Pierce (1930) found this species laying eggs on
the new lateral stems of Siderqntius species. The larvae feed in the
stems, surrounded by plant fragments and debris. Pupation occurs in
the tips of the stem or in the main stem. The insects can be so numerous
that they completely riddle the stem in which they are breeding.
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