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Excerpts from: Hutchings, G.E., 2004. Egg-Laying Efficiency of Osmia lignaria propinqua Cresson (Hymenoptera: Megachilidae) In Relation To Three Different Channel Lengths of Domatia. unpublished. Hutchings, G.E., 2005. An Increase in Female Offspring of the Orchard Mason Bee (Osmia lignaria propinqua Cresson) In Relation To Deeper Channel Length: Manipulating Sex Ratio to Enhance Pollination. Unpublished
The Orchard Mason Bee,
by Gord Hutchings, 2010. All photos by Norm and Gord Hutchings
Osmia lignaria propinqua Cresson is distributed throughout Southwestern Canada and Western United States, extending to approximately 100˚W longitude. This bee species along with many other native species, play an integral role in the pollination system in North America. Similar to many parts of the globe, a North American pollination crisis looms due to loss of habitat and altered plantpollinator interactions critical for crop production (Kremen & Ricketts 2000). O.l. propinqua is a univoltine (one generation per year) species and has a protandrous emergence (males emerge before females – usually), in early spring, triggered by suitable conditions and temperatures of approximately 13˚-15˚C. The sexes are dimorphic with the male being smaller and much shorter lived – the males being one of the first bees to emerge in the spring (Torchio 1989). The male emerges a few days earlier than the females and awaits nearby, sensing the female's emergence by detecting pheromones she elicits (Torchio 1989). The male immediately grasps the emerging female, often forcing copulation at a time when she is least able to fight him off. She may mate more than once during the first day but is ignored by males henceforth as she begins searching for a nest. A suitable nest may consist of a large fissure in the bark of a tree, a hollow, hardened stem of a plant, or any orifice of suitable width and depth. Preferred nesting sites can consist of abandoned insect burrows excavated in trees or wood (Torchio & Tepedino 1980). Human-made provisions may consist of cracks in buildings, splits between roof or wall siding, holes where objects have been removed such as a large nail or bolt, open and exposed hoses, and any other orifice that might be suitable for a nest (Williams 2003). In Victoria, B.C., insurance adjusters have been called to the scene of suspected tamperings at building sites after inspection holes were filled in with mud by these bees (T. Burdge, personal communication, 2002). After she finds a suitable nesting cavity, the female locates a source of wet, inorganic mud (clay) and forms this into a ball with her mandibles. She carries this load into the nest where it is kneaded to the consistency necessary for constructing a foundation for a cell partition either at the channel bottom, or sometimes part way up from the bottom (Fig. 1a). If the first mud layer begins at the very end of the
channel, it is referred to as the preliminary plug, keeping the developing larva off the substrate behind the pollen. This preliminary plug is smoothed using her head tubercles and mandibles. She eventually forms a bottom to the first cell layer which usually requires between eight to 12 mud-collecting trips for each cell partition, depending on the channel width and the size of the female (Torchio 1989). Next, comes the provision of pollen and nectar laid down in each cell in which the developing larva will feed (Fig. 1d). Pollen-nectar collecting trips to a variety of flowering plants number from 14-35 to provision each cell, depending on the channel width as well as the sex of the egg she will lay. If a female egg is oviposited, more pollen and nectar are provided to sustain this larger sex bee. Pollen transported to the nest using the scopa on the venter of the abdomen, is scraped off next to the cell bottom with the use of the hind legs. Nectar is regurgitated from her crop. A single curved egg is oviposited directly on this pollen-nectar mixture where it remains attached on end (Fig. 1e).
Figure 1. Lateral view of nest cells of Osmia lignaria propinqua. (a) mud foundation circumference; (b) initial bottom layer of cell; (c) built-up second layer; (d) provision of pollen and nectar; (e) second foundation circumference laid down plus oviposition of egg attached upright on pollen and nectar provision; (f) bottom layer of next cell in line which acts as a lid to the current cell; (g) final vestibular cell and closing channel at end of channel. Note: size of ~F=1 cm (female); ~M=1 cm (male)
Finally, the lid of the cell is deposited,which can also be the adjacent bottom of the next adjoining cell (Fig. 1f). If it is the final cell to be enclosed, a vestibular cell is created which is a space before the
closing plug (Fig. 1g). This closing plug is slightly thicker than the previous partitioning cell division walls. From trials in a greenhouse, as many as 38 cells can be constructed by a single female with a maximum of nine cells per day, whereas in the field only one or two cells are formed per day (Torchio, 1989). Within the channel, as eggs are laid, the female progeny are produced at the start of the channel (to the rear), with males being produced further along (Fig. 2). Males are produced if the females are not fertilized or resources are diminished. These patterns are directly attributable to factors such as (i) females flying late in the flight period, (ii) channel widths being too small in diametre or (iii) when weather conditions are unfavourable (Krombein 1967; Torchio & Tepedino, 1980). Also the confining width of a channel for large females constricts the muscles controlling egress of sperm from the spermathaecae and results in an unfertilized egg (Krombein 1967). Intercalary cells lacking provisions, are sometimes found in channels either as a result of usurpation (taken over/stolen) by another female or if one bee does not return to her brood. When a new female takes over a previously utilised channel, she leaves this intercalary cell space, laying down a preliminary cell to begin a new series of cells (Fig.2B).
Figure 2. Lateral view of linear cell construction. (A): Approximate 12.5 cm section of channel showing females near the rear and males at the front with the final closing plug and vestibular cell. Male provisioned cells are slightly smaller than female provisioned cells. (B): A linear section of channel showing an intercalary cell where a second female usurped or superseded the first series of cells.
Larvae develop within the cell, going through five moults until the provision of food has been consumed. At the final instar, the larva orients its direction within the cell by contacting the surface of the cell partitions. When the female initially lays down the mud and smooths the inside surface, the outside surface (inside of first cell), remains rough since she lacks access to that surface. The larva then spins a cocoon, rests as a prepura with its head toward the rough surface and metamorphoses into a
fully formed adult. Transformation from egg to adult takes about 16 weeks, at which time the adult remains in a reproductive diapause state over the winter (Torchio & Tepedino 1980; Tepedino & Torchio, 1982). Female cocoons are larger than male cocoons and are never located at the channel entrance. Series of smaller cocoons throughout the entire channel are indications of an unfertilized female that only produce males.
Figure 3. Typical stacked tray style condo manufactured by humans to encourage Osmia as well as other solitary bees, to utilise. This style of condo can be dismantled for ease of cocoon extraction for the cleaning process to rid the contents of mites and other parasitoids.
Figure 4. A female turning around at the entrance to back down into her channel. She scrapes the pollen off the venter of her abdomen using her rear legs.
Figure 5. An experiment in egg-laying efficiency by adult females, looking into what length they will oviposit more females than males. These double-ended condos were on a south-facing wall, with entrances pointing east and west, to maximize, or to see if there was a difference, in activity preferences by the egg-laying females.
Figure 6. Filled channels showing mud divisions, pollen and nectar provision as well as egg, for each cell. Note the different colours of pollen even within one provision, demonstrating the cross-pollinating of the females as they visit flowers. They are superior pollinators than most other flower-visitors in the insect world.
Figure 7. Developing larva within its cell, consuming the pollen provision provided by its mother.
Figure 8. Developing larvae nearing its maximum size and then commencing to spin its cocoon. They will stay within this cocoon, metamorphosing into an adult bee and diapausing over the winter, ready to emerge the following Spring.
Figure 9. Bee-keepers in the late Fall or Winter, dismantle the condos, extract the cocoons and then cleaning the mites off the cocoons using the sand method. ("How To Clean Orchard Mason Bees Using Sand", video on Youtube (http://www.youtube.com/watch?v=PrZkT9cC99k&feature=related). At this time, the condos themselves can be sterilised of any debris, mites, or mould and left assembled and dry, ready for next Spring.
Figure 10. Clean cocoons after the sand-cleaning method, ready for next year. Typically, larger cocoons are females and smaller cocoons are males.
References: Hutchings, G.E., 2004. Egg-Laying Efficiency of Osmia lignaria propinqua Cresson (Hymenoptera: Megachilidae) In Relation To Three Different Channel Lengths of Domatia. unpublished. Hutchings, G.E., 2005. An Increase in Female Offspring of the Orchard Mason Bee (Osmia lignaria propinqua Cresson) In Relation To Deeper Channel Length: Manipulating Sex Ratio to Enhance
Pollination. Unpublished Krombein, Karl V., 1967. Trap-Nesting Wasps and Bees – Life Histories Nests and Associates. Smithsonian Press, Washington, D.C. Kremen, Claire and Taylor Ricketts. 2000. Global Perspectives on Pollination Disruptions. Conservation Biology, 14(5): 1226-1228. Tepedino, V.J. and P.F. Torchio, 1982. Temporal Variability in the Sex Ratio of a Non-Social Bee, Osmia lignaria propinqua: Extrinsic Determination or the Tracking of an Optimum? Oikos 38: 177182. Tepedino, V.J. and P.F. Torchio, 1989. Influence of Nest Hole Selection on Sex Ratio and Progeny Size in Osmia lignaria propinqua (Hymenoptera: Megachilidae). Annals of the Entomological Society of America 82(3): 355-360. Tepedino, V.J. and P.F. Torchio, 1994. Founding and Usurping: Equally Efficient Paths to Nesting Success in Osmia lignaria propinqua (Hymenoptera: Megachilidae) Annals of the Entomological Society of America 87(6): 944-953. Torchio, P.F., 1989. In-Nest Biologies and Development of Immature Stages of Three Osmia Species (Hymenoptera: Megachilidae). Annals of the Entomological Society of America 82(5): 599-614. Torchio, P.F. and V.J. Tepedino, 1980. Sex Ratio, Body Size and Seasonality in a Solitary Bee, Osmia lignaria propinqua Cresson (Hymenoptera: Megachilidae). Evolution, 34(5), 995-1003. Williams, N.M., 2003. Use of Novel Pollen Species by Specialist and Generalist Solitary Bees (Hymenoptera: Megachilidae). Oecologia 134: 228-237.