Nesting site density and distribution affects Osmia lignaria (Hymenoptera: Megachilidae) reproductive success and almond yield in a commercial orchard.

Authors: Artz, Derek; ALLAN, MATTHEW - Pacific Pollination, Llc; WARDELL, GORDON - Paramount Farming Company, Inc; Pitts Singer, Theresa

Submitted to: Insect Conservation and Diversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2013
Publication Date: 3/11/2013
Citation: Artz, D.R., Allan, M.J., Wardell, G.I., Pitts Singer, T. 2013. Nesting site density and distribution affects Osmia lignaria (Hymenoptera: Megachilidae) reproductive success and almond yield in a commercial orchard.Insect Conservation and Diversity.doi:10.1111/icad.12026

Interpretive Summary: Of all of the animal pollinators, bees are the most important pollinators in agricultural systems. Many of the insect-pollinated crops rely solely on honey bees to provide the majority of pollination services. Because of the decline of honey bee populations in the U.S., the pressure to supply so many honey bees for orchard crops could be alleviated by other bee species that are equally or more efficient pollinators. One species that is being developed for managed pollination is the blue orchard bee. The potential of commercially-managed, native blue orchard bees to augment honey bees in orchard pollination depends on a suite of factors, particularly how to enhance blue orchard bee retention while optimizing even pollination throughout the orchard by varying their stocking density and nesting distribution within orchards. In 2011, we investigated how artificial nest box density and the number of cavities within nest boxes influenced blue orchard bee retention and reproduction in a 61 ha almond orchard pollinated by a mixture of blue orchard bees and honey bees in the southern Central Valley of California. We assessed how localized blue orchard bee nesting affected total nut yield. Retention of blue orchard bee females was significantly greater in orchard areas with high density nest boxes compared to areas with low density nest boxes. Females preferred nesting in high density (low cavity) nest boxes compared to low density, high cavity nest boxes. All measures of blue orchard bee reproductive success (e.g., number of completed nests, number of cells, and sex of offspring) were greater in orchard areas with high density nest boxes than areas with low density nest boxes. Therefore, the distribution of nest sites in an orchard is an important consideration for managing and sustaining blue orchard bee populations for orchard pollination.

Technical Abstract: Continued declines in honey bee Apis mellifera populations have prompted further exploration of alternative, economically-viable managed bee pollinators of agricultural crops. The potential of commercially-managed, native blue orchard bees Osmia lignaria to augment honey bees in orchard pollination depends on a suite of factors, particularly how to enhance O. lignaria retention while optimizing even pollination throughout the orchard by varying their stocking density and nesting distribution within orchards. In 2011, we investigated how artificial nest box density and the number of cavities within nest boxes influenced O. lignaria retention and reproduction in a 61 ha almond orchard pollinated by a mixture of O. lignaria and A. mellifera in the southern Central Valley of California. We assessed how localized O. lignaria nesting affected total nut yield. Retention of O. lignaria females was significantly greater in orchard areas with high density nest boxes compared to areas with low density nest boxes. Females preferred nesting in high density (low cavity) nest boxes compared to low density, high cavity nest boxes. Although considerable nesting variation occurred between treatments and within the orchard, all measures of O. lignaria reproductive success (e.g., number of completed nests, number of cells, and sex of offspring) were greater in orchard areas with high density nest boxes than areas with low density nest boxes. Understanding the factors of O. lignaria retention, nest establishment and reproduction, pre-emerged vs. on-site emergence from cocoons, and the spatial and temporal distribution of bees in orchards will allow for designing better O. lignaria management strategies for use in large conventional orchards.