BEST LITTLE ORCHARD BEE IN TEXAS:
Life History, Population Structure, Management,
& Commercial Status of a Promising Blueberry Pollinator,
Overwintering: Oct - Feb
Calaveras Co. CA
Life History and Population Structure:
Species (subspecies): Osmia ribifloris ribifloris (TX)
Osmia ribifloris biedermannii (AZ –CA), see map inset
Population Structure: TX and CA populations are more closely related,
suggesting a north-south subspecific split occurred
between 0.9 –1.4 mya during the early Pleistocene
Description: iridescent green or blue megachilid bee (Fig. A)
Distribution: Upland sites & foothills in TX, AR, CA, OR, UT (see map)
Niche: solitary, univoltine, protandrous & xylophilic oligolege of
Ericaceae & Berbidaceae
Floral Host Records: Vaccinium (Fig. B), Arctostaphylos, Diospyros, Rosa,
Cercis, Sophora, Berberis, Mahonia
Brood Size per female: 16 –22 progeny in 2 -3 straws (Fig. D):
Female production: 1 per 2.7 males in captivity (Figs. D & E)
Cocoon Weight: male 60 –90 mg, female 120 –180 mg (Fig. F)
Diapausal requirements: 90 –120 days @ 6oC (43oF). Bees
from higher latitudes that we tested in MS required
artificial cooling. Pre-emergence mortality plus post-
emergence mortality was low (<8%).
Incubation-emergence interval: 4 –8 days depending on length of diapause
and incubation temperature (recommended: 21 –29oC
or 70 –85oF)
Incubation to nesting interval: 10 days
Courtship and post-copulatory bonding: lasts 30 –90 minutes
Emergence Period: February –March, synchronous with bloom
Pollination period (when bees are active): 28 –35 days
Thermal threshold for flight: 9oC (48oF)
Pollination efficiency (single visit fruit set): 50 % –75%, comparable to a benchmark pollinator,
the southeastern blueberry bee
Preferred nesting habitat: cavities in wood, cardboard, particleboard, other fibers (Figs. E)
Reliable nest block designs: solid wood (pine), wood laminates, hollow boxes (Fig. D), bundled reeds.
Acceptable tolerances for nest cavity size: 6 – 9 mm (1/4” – 3/8”) interior diameter (preferred: 6 – 7 mm) 7.5 –15.0
cm (3 – 6”) depth (preferred: 15.0 cm)
Recommended leaf sources for bees to fashion partitions and entrance plugs: ranked by preference: Rosa (Fig.
C), Vaccinium, Quercus, Rubus, Fragaria and perhaps other leaf sources with shiny waxy surfaces.
Color of nest blocks: white (acrylic or latex paint) that contrast with dark colored nest entrances.
Factor that will most limit population growth on-farm: Pre-nesting female dispersal, high male sex ratios due to likely
matched matings and homozygosity at the sex-determining locus (Figure 2).
Natural enemies of concern: Chaetodactylus mites (Fig. F), birds, lizards, ants, chalcid parasitoids, chalkbrood
United States Department of Agriculture - Agricultural Research Service
Thad Cochran Southern Horticultural Laboratory, Southern Research Horticultural Unit, Poplarville MS 39470
Pollinating Insects - Biology, Management, Systematics, and Research Unit, Logan UT 84322
Pollinator Status for Osmia ribifloris:
-Native US Bee
-Not an endangered species, but wild populations are
limited by host and nest site availability. Wildfires
can destroy trap-nesting stations established in chaparral
-Evaluated as a blueberry pollinator in
California on highbush types (1990)
Maine on lowbush clones (1994)
Alabama on rabbiteye cultivars (1995 - 1997)
Mississippi on wild, rabbiteye
& southern highbush types (1998 –2006)
-Not commercially available to US blueberry producers.
-Release in blueberry growing areas outside the bees
native range unlikely in the foreseeable future.
-California and Oregon farmers have a unique opportunity
to easily manage this locally available and docile bee for
blueberry pollination, in tandem with Osmia lignaria in
almond orchards. Both of these Osmia spp. have similar
-Other native US Osmia species are being evaluated as
commercial fruit pollinators (O. chalybea and O. lignaria).
Courtship: Feb - Mar Nesting: Mar - April Nesting: Mar - Apr Brood Development: Apr - Aug
Blair J. Sampson, James H. Cane, Christopher T. Werle, Timothy A. Rinehart & John J. Adamczyk
Figure 1. Parsimony cladogram of aligned (by Clustal W method) paternal mtDNA (COI) nucleotide sequences for 14 adult individuals from
four distinct subgroups of Osmia ribifloris (C,UT, UT, MS, CA,TX). Fully resolved branches are depicted with bootstrap support. Population
designations are as follows: California: (CA), Mississippi (MS), Texas (TX), Utah (UT), and the outgroup Osmia lignaria (T2, not shown).
years in isolation (n = 5)
2000 2001 2002 2003 2004 2005
y = 2.58 + 0.04e0.59x
Figure 2. Increasing male-bias in
post-emergence sex ratios for
captive O. ribifloris. Sex ratios of
newly arriving bees (parental
stock) shipped in 2000 and 2001
were excluded from this analysis.