Abstract:
One of the most common bee genera in the Niagara Region, the genus Ceratina
(Hymenoptera: Apidae) is composed of four species, C. dupla, C. calcarata, the very rare
C. strenua, and a previously unknown species provisionally named C. near dupla. The
primary goal of this thesis was to investigate how these closely related species coexist
with one another in the Niagara ~ee community. The first necessary step was to describe
and compare the nesting biologies and life histories of the three most common species, C.
dupla, C. calcarata and the new C. near dupla, which was conducted in 2008 via nest
collections and pan trapping. Ceratina dupla and C. calcarata were common, each
comprising 49% of the population, while C. near dupla was rare, comprising only 2% of
the population. Ceratina dupla and C. near dupla both nested more commonly in teasel
(Dipsacus sp.) in the sun, occasionally in raspberry (Rubus sp.) in the shade, and never in
shady sumac (Rhus sp.), while C. calcarata nested most commonly in raspberry and
sumac (shaded) and occasionally in teasel (sunny). Ceratina near dupla differed from
both C. dupla and C. calcarata in that it appeared to be partially bivoltine, with some
females founding nests very early and then again very late in the season.
To examine the interactions and possible competition for nests that may be taking
place between C. dupla and C. calcarata, a nest choice experiment was conducted in
2009. This experiment allowed both species to choose among twigs from all three
substrates in the sun and in the shade. I then compared the results from 2008 (where bees
chose from what was available), to where they nested when given all options (2009
experiment). Both C. dupla and C. calcarata had the same preferences for microhabitat and nest substrate in 2009, that being raspberry and sumac twigs in the sun. As that
microhabitat and nest substrate combination is extremely rare in nature, both species must
make a choice. In nature Ceratina dupla nests more often in the preferred microhabitat
(sun), while C. calcarata nests in the preferred substrate (raspberry). Nesting in the
shade also leads to smaller clutch sizes, higher parasitism and lower numbers of live
brood in C. calcarata, suggesting that C. dupla may be outcompeting C. calcarata for the
sunny nesting sites.
The development and host preferences of Ceratina parasitoids were also
examined. Ceratina species in Niagara were parasitized by no less than eight species of
arthropod. Six of these were wasps from the superfamily Chalcidoidea (Hymenoptera),
one was a wasp from the family Ichneumonidae (Hymenoptera) and one was a
physogastric mite from the family Pyemotidae (Acari). Parasites shared a wide range of
developmental strategies, from ichneumonid larvae that needed to consume multiple
Ceratina immatures to complete development, to the species from the Eulophidae
(Baryscapus) and Encyrtidae (Coelopencyrtus), in which multiple individuals completed
development inside a single Ceratina host. Biological data on parasitoids is scarce in the
scientific literature, and this Chapter documents these interactions for future research.
