Summary1. Pan traps or water traps have been used widely to sample agricultural insect pests, but no formal studies have assessed the utility of these traps as sampling devices for bees.2. Coloured pan traps, used as flower models, can efficiently and selectively sample an oligolectic bee, Andrena (Hesperandrena) limnanthis, and other bees associated with white‐flowered Limnanthes douglasii rosea.3. Females and males of A. limnanthis unexpectedly exhibit different colour preferences. Females are strongly attracted to white and blue traps, but discriminate against yellow traps. Males prefer white traps over blue and yellow traps. Consequently, blue traps are selective for females only, while white traps are selective for both sexes.4. Non‐A. limnanthis bees were caught in significantly greater numbers in yellow than in blue or white traps. These bees included generalists, as well as specialists that are oligolectic on mostly yellow‐flowered species.5. Colour of traps had a significant effect on the numbers of A. limnanthis females and males, and non‐A. limnanthis bees caught in traps. These results indicate that quantitative sampling of bees by pan trap methods can be highly sensitive to trap colour.

No abstract

1. Measurements of pollinator performance are crucial to pollination studies, enabling researchers to quantify the relative value of different pollinator species to plant reproduction. One of the most widely employed measures of pollinator performance is single‐visit pollen deposition, the number of conspecific pollen grains deposited to a stigma after one pollinator visit. To ensure a pollen‐free stigma, experimenters must first bag flowers before exposing them to a pollinator. 2. Bagging flowers, however, may unintentionally manipulate floral characteristics to which pollinators respond. In this study, we quantified the effect of bagging on nectar volume in watermelon (Citrullus lanatus) flowers, and how this affects pollinator performance and behaviour. 3. Experimental bagging resulted in roughly 30‐fold increases in nectar volume relative to unmanipulated, open‐pollinated field flowers after only a few hours. Honey bees, but not native bees, consistently displayed elevated handling times and single‐visit pollen deposition on unmanipulated bagged flowers relative to those from which we removed nectar to mimic volumes in open‐pollinated flowers. 4. Furthermore, we identify specific bee foraging behaviours during a floral visit that account for differences in pollen deposition, and how these differ between honey bees and native bees. 5. Our findings suggest that experimental bagging of flowers, without accounting for artificially accumulated nectar, can lead to biased estimates of pollinator performance in pollinator taxa that respond strongly to nectar volume. We advise that pollination studies be attentive to nectar secretion dynamics in their focal plant species to ensure unbiased estimates of pollinator performance across multiple pollinator species.

As a restoration strategy, translocation of endangered plant populations may be a risky procedure with uncertain outcomes. Often, very little ecological information is known about these populations before, as well as after, translocation. The endangered vernal pool plant, Blennosperma bakeri, is a case in point. As a consequence of vernal pool habitat destruction, many populations of B. bakeri have been transplanted or translocated to various receptor sites. In this study, we examine the incidence of a thrips herbivore, Frankliniella minuta, in natural and translocated populations of B. bakeri in relation to floral patch size and degree of isolation and present implications for B. bakeri restoration and management. At a vernal pool mitigation site in California, U.S.A., thrips were present in both kinds of B. bakeri populations, and the range of thrips densities in both kinds of populations was similar for adults and immatures. Significant negative relationships between patch size, patch isolation, and numbers of flower heads infested with adult or immature thrips were found only among natural patches. Natural patches tended to be smaller in size than translocated patches, but patch isolation distances were similar. Some evidence suggests that B. bakeri is a F. minuta host plant, but the impact of these herbivores on B. bakeri remains unclear. Our findings, although preliminary, suggest that the distribution and abundance of F. minuta varied with floral patchiness, thrips stage, and the natural or translocated status of B. bakeri populations. In addition, our results provide a starting point for understanding the spatial context of plant–herbivore interactions in artificially altered vernal pool landscapes.