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Agricultural expansion and intensification negatively affect pollinator populations and has led to reductions in pollination services across multiple cropping systems. As a result, growers and researchers have utilized the restoration of local and landscape habitat diversity to support pollinators, and wild bees in particular. Although a majority of studies to date have focussed on effects in pollinator-dependent crops such as almond, tomato, sunflower, and watermelon, supporting wild bees in self-pollinated crops, such as grapes, can contribute to broader conservation goals as well as provide other indirect benefits to growers. This study evaluates the influence of summer flowering cover crops and landscape diversity on the abundance and diversity of vineyard bee populations. We showed that diversity and abundance of wild bees were increased on the flowering cover crop, but were unaffected by changes in landscape diversity. These findings indicate that summer flowering cover crops can be used to support wild bees and this could be a useful strategy for grape growers interested in pollinator conservation as part of a broader farmscape sustainability agenda.

Native bees are important ecologically and economically because their role as pollinators fulfills a vital ecosystem service. Pollinators are declining due to various factors, including habitat degradation and destruction. Grasslands, an important habitat for native bees, are particularly vulnerable. One highly imperiled and understudied grassland type in the United States is the Pacific Northwest Bunchgrass Prairie. No studies have examined native bee communities in this prairie type. To fill this gap, the bee fauna of the Zumwalt Prairie, a large, relatively intact remnant of the Pacific Northwest Bunchgrass Prairie, was examined. Native bees were sampled during the summers of 2007 and 2008 in sixteen 40-ha study pastures on a plateau in northeastern Oregon, using a sampling method not previously used in grassland studies—blue vane traps. This grassland habitat contained an abundant and diverse community of native bees that experienced marked seasonal and inter-annual variation, which appears to be related to weather and plant phenology. Temporal variability evident over the entire study area was also reflected at the individual trap level, indicating a consistent response across the spatial scale of the study. These results demonstrate that temporal variability in bee communities can have important implications for long-term monitoring protocols. In addition, the blue vane trap method appears to be well-suited for studies of native bees in large expanses of grasslands or other open habitats, and may be a useful tool for monitoring native bee communities in these systems.

The long-term goal of this study was to use solitary bees to assess the impact of advancing Africanized honey bees (Apis mellifcra scutcllata Lepeletier) on the native California bee fauna. Cavity-nesting, solitary bee species were systematically monitored in wooden trap nests at 6 sites in northern central California from 1990 to 1992. Three sites were in the San Joaquin Valley in wildlife refuges or preserves; 3 were in coastal mountain or Sierran foothill parks or reserves. Differences in frequencies of nesting bees were observed and recorded among sites and habitats through time. A Poisson regression indicated that all explanatory variables and their 1st order interactions were highly significant. There were significant differences among bee taxa, sites and years, and their interactions (bee X site; bee X year; site X year). Mcgachile species were the predominant cavity nesters in the 3 valley sites; Osmia species were the common group in coastal mountain I foothill sites. In a computer simulation, using a variation of the Poisson regression, several significant differences were also observed between yearly frequency counts for certain bee species at the same site. Possible reasons for year to year changes included differential natural mortality, extreme annual weather patterns, use of marginal habitats, and negative impacts from exotic solitary bee species. Three exotic megachilids (Mcgachile rotundata (F.), M. apicalis Spinola, and M. concinna Smith) have successfully invaded and become established in California. Possibly, M. apicalis has affected other cavity nesting bee species, including the exotic M. rotundata in our Central Valley sites.

Temporal and spatial characteristics of a community of cavity nesting megachilid bee species and their introduced competitors were examined at a site in the Central Valley of California. Two of the introduced bee species, Megachile apicalis Spinola and Megachile rotundata (F.), were frequent nest site occupants and accounted for 19.6 and 3.4% of all artificial nesting cavities (trap-nests) monitored during the 1st and 2nd yr of this study, respectively. These species were most active before and after the peak in native bee nesting activity and tended to occupy xeric habitats, despite significantly higher larval mortality associated with such environments. The ability to occupy a wide array of habitats may account for the invasion success of M. apicalis in California. Another invader, the European earwig, Forficula auricularia L., was a frequent occupant of nesting cavities in mesic habitats, accounting for 59 and 85% occupancy of trap-nests during the 1st and 2nd yr of the study, respectively. Exclusion experiments indicate earwig densities were sufficient to displace female bees at nest sites with 113 as much nesting activity occurring in sampling units that allowed entry by earwigs as those made inaccessible to them with sticky barriers. In comparison, all native species (including bees and wasps) never accounted for >25% of all occupied nesting cavities of either monitoring period of the study.

High and low pollen-hoarding strains of honey bees were selected based on quantity of pollen stored in combs. Performance of strains in commercial alfalfa seed pollination is reported. After three generations of selection, colonies with instrumentally inseminated high-strain queens stored significantly more pollen (2.4-fold) than low-strain colonies. Similarly, colonies from naturally mated, outcrossed high-strain queens stored more pollen (2.4-fold) than outcrossed low-strain colonies. Selection did not change preferences for sources of pollen. After four generations of selection, colonies with naturally mated high-strain queens outcrossed with commercial drones stored significantly more pollen (l.4-fold) than commercial colonies. Rates of queen acceptance (54 and 61%) and overwintering survival (61%) in commercially managed colonies were surprisingly low, indicating 37% queen survival during a 10-mo period. Overwintered outcrossed high-strain colonies were more populous than commercial colonies at the beginning of almond bloom.

A cluster count method for estimating honey bee, Apis mellifera L., colony strength is presented in contrast to intensive frame-by-frame evaluations. Correlation coefficients between the two methods were highly significant for 5 yr. Cluster counts are recommended to growers and beekeepers involved in pollination contracts as a simple, rapid, economic evaluation method which is not excessively disruptive to the colony. The observed adult honey bee colony populations can be estimated accurately by using the derived regression equation. The relation of cluster and intensive count to the brood area is discussed.

The rate of flight and the foraging profiles of worker honey bees, Apis mellifera L., in disposable pollination units (DPU's) and overwintered colonies were compared. Because of population decline and lower total foraging indices, approximately 1.5 to 2 times as many DPU bees were required to match the foraging activity of overwintered colonies. Low ambient temperatures appeared to restrict the flight activity of DPU bees; higher temperatures (above about 21°C) stimulated disproportionately higher flight activity from the DPU's and 4-frame colonies.

Pollen traps that remove pollen loads from returning forager bees changed foraging patterns for hives in almond and prune orchards. Hives with traps had greater numbers of pollen foragers and higher proportions of foraging bees with pollen loads-than hives without traps. This effect was greatest before ca. 3:00 p.m. Hives with traps had less increase in capped brood and in the adult population than did hives without traps at the end of a 48-day period.

A population of Osmia cornuta Latr. was trapped in northern Spain during 1984, transported to the United States, quarantined, exposed to various temperature regimes through summer months, and placed in California almond orchards through winter months. Results of this study demonstrated that bees overwintered in commercial almond orchards emerged in synchrony with almond bloom; gregarious nesting was expressed; immatures developed normally on provisions composed mostly of almond pollen and nectar resources; prewintering temperatures affected winter survival of parent bees; and populations that had the highest rates of winter mortality produced the fewest number of cells per emerged female.

Mean flight activity from overwintered Apis mellifera L. colonies was usually greater and the quantity of pollen trapped was well in excess of that from disposable pollination units (DPU's). However, comparisons between individual units indicated that DPU's exhibit more uniform flight activity than colonies. Data pertinent to the effect of this atypical domiciliary crowding and colony makeup on longevity, development, and certain behaviorial adaptations of the bees are included.

Andrena placida Smith nests in compacted sand cliffs near the ocean in Marin County, California. The bees are vernal and polylectic. The chromosome numbers are n = 5 (♂) and 2n = 10 (♀). Comparisons with A. erythronii Robertson reveal that the 2 species are very similar in their biological characteristics and in structural features of their postdefecating larvae, and pupae.

Pithitis smaragdula (F.) is a bright green, small carpenter bee which is widespread in the oriental region and is known to pollinate economically important plants, especially legumes and cucurbits. About 300 bees imported from Ludhiana, India, were released 10 April 1969, at Davis, California. Subsequent collecting during the 1st season confirmed that one or more generations of the bees had been reared and that Trifolium repens L. was visited for pollen. Although the overwintering bees under observation died from unknown causes, and no living bees were found in 1970, it is possible that the bees survived elsewhere. Ecological factors believed to be important in the establishment of the colony were: few natural enemies, low competition for food, high competition for nesting sites, and a cooler, drier climate than the native habitat. Future releases are planned for warmer areas in the State.

The highest unexplained mortality of immature Megachile rotundata (F.) occurs in alfalfa-seed fields. Water-soluble saponins from alfalfa leaves, used to line bee brood cells, seemed capable of causing such mortality. Food masses of bee nests from non-alfalfa areas were injected with extracts of leaves from alfalfa plants selected for high or low saponin content. Mortality after injection with these extracts averaged 56.2 and 37.8%, respectively, and that for controls and uninjected cells averaged 29.0 and 5.9%, respectively. This relationship was consistent for 6 different extracts. Purified alfalfa saponins produced bee mortality directly related to saponin concentration. Suggestions to improve bee survival for alfalfa seed production include: selecting low saponin alfalfa lines, increasing bee populations on clovers, and providing alternative leaf forage near alfalfa seed fields.