http://www.sussex.ac.uk/lifesci/goulsonlab/documents/goulson-et-al-biological-conservation-2005.pdf

Causes of rarity in bumblebees

Planted meadows are increasingly used to improve the biodiversity and aesthetic amenity value of urban areas. Although many ‘pollinator-friendly’ seed mixes are available, the floral resources these provide to flower-visiting insects, and how these change through time, are largely unknown. Such data are necessary to compare the resources provided by alternative meadow seed mixes to each other and to other flowering habitats. We used quantitative surveys of over 2 million flowers to estimate the nectar and pollen resources offered by two exemplar commercial seed mixes (one annual, one perennial) and associated weeds grown as 300m2 meadows across four UK cities, sampled at six time points between May and September 2013. Nectar sugar and pollen rewards per flower varied widely across 65 species surveyed, with native British weed species (including dandelion, Taraxacum agg.) contributing the top five nectar producers and two of the top ten pollen producers. Seed mix species yielding the highest rewards per flower included Leontodon hispidus, Centaurea cyanus and C. nigra for nectar, and Papaver rhoeas, Eschscholzia californica and Malva moschata for pollen. Perennial meadows produced up to 20x more nectar and up to 6x more pollen than annual meadows, which in turn produced far more than amenity grassland controls. Perennial meadows produced resources earlier in the year than annual meadows, but both seed mixes delivered very low resource levels early in the year and these were provided almost entirely by native weeds. Pollen volume per flower is well predicted statistically by floral morphology, and nectar sugar mass and pollen volume per unit area are correlated with flower counts, raising the possibility that resource levels can be estimated for species or habitats where they cannot be measured directly. Our approach does not incorporate resource quality information (for example, pollen protein or essential amino acid content), but can easily do so when suitable data exist. Our approach should inform the design of new seed mixes to ensure continuity in floral resource availability throughout the year, and to identify suitable species to fill resource gaps in established mixes.

/pdf/food-for-pollinators-quantifying-the-nectar-and-pollen-qbdrifcoid.pdf

Food for Pollinators: Quantifying the Nectar and Pollen Resources of Urban Flower Meadows

The ecology of all bumblebees (Bombus spp.) is similar, yet some species have declined greatly while others remain abundant. We examine whether abundance is related to diet breadth. The floral visits of bumblebees were examined on Salisbury Plain, UK. All of the species examined gathered pollen mostly from Fabaceae. All species gathered nectar from a broader range of flowers than they did pollen, and longer-tongued bees had a narrower diet breadth when collecting nectar. B. hortorum (the species with the longest tongue) specialized on Trifolium pratense. As predicted, abundant species had a broader diet than rare species. Species with similar-length tongues visiting similar flowers. However, interspecific competition did not appear to be important since species with similar tongue lengths and high niche overlap co-occurred at high abundance. We suggest that the rare species may be those with short colony cycles, in which dependence on high quality food to rear larvae quickly forces specialization.

/pdf/niche-overlap-and-diet-breadth-in-bumblebees-are-rare-2tpv02qovr.pdf

Niche overlap and diet breadth in bumblebees; are rare species more specialized in their choice of flowers?

Many of the reported pesticide incidents involving honeybees probably also result in mortality of bumblebees and, together with a reduction in suitable habitat, these have resulted in the decline in bumblebees in the UK over the last 20 years. Applications of sprays, e.g. pyrethroids, to flowering crops or weeds at times when honeybees are less active are likely to result in unre- ported bumblebee deaths. There is a need to protect foraging bumblebees from direct overspray dur- ing the early morning and late evening when pesticides which are repellent but highly toxic are applied, i.e. pyrethroids. Of particular concern are those pesticides applied when queens are emerg- ing and establishing colonies, e.g. March/April, when colonies may be significantly impacted by the loss of a small number of workers or the queen. This is a problem which cannot readily be addressed by risk management measures due to differing foraging profiles of honeybees and bum- blebees but does need to be taken into account in risk assessment and the development of more selective compounds. Bombus / pesticides / exposure / toxicity / risk assessment

/pdf/assessing-the-exposure-and-toxicity-of-pesticides-to-2kzuz8tx7w.pdf

Assessing the exposure and toxicity of pesticides to bumblebees (Bombus sp.)

Bumblebees are important pollinators of many crops and wild flowers and there are both conservation and economic reasons for taking action to assess the impact of pesticides on bumblebees. Pesticide risk assessments for honeybees are based on hazard ratios which rely on application rates and toxicity data and are unlikely to be appropriate for bumblebees. Bumblebees are active at different times and on different crop species and are, therefore, likely to have different exposure profiles. Unlike honeybees, deaths of bumblebees due to pesticides are unlikely to be reported, since the bees are not kept domestically and will die in small numbers. This paper highlights the differences in the potential risk posed by pesticides to bumblebees from that of honeybees. This is based on their exposure through use of crops and flowering weeds and on available data on toxicity of pesticides. This information is also intended as a source document for information on the foraging behavior and phenology of bumblebees for use in risk assessment for pesticides.

Extrapolating from Honeybees to Bumblebees in Pesticide Risk Assessment

SUMMARYThe seasonal phenology of six Bombus species and four Psithyrus species is given for a site to the west of London, UK, for five years from 1985 to 1989. The emergence in spring of Bombus spp. queens was linked to periods with air temperatures above 11°C. During the five-year survey a mean maximum temperature of 12.1°C occurred during the week of initial oviposition, an increase of 1.9°C from the week preceding ovipositon. The colonies of Bombus spp. matured at different times: early-season during June, mid-season in early August and late-season in August or early September. The period between the emergence of queens and of their workers and males was on a progressive scale, from species maturing early to those maturing in mid-season. This is consistent with the increasing lengths of their colony cycles. Workers and males of the long-season bumble bees emerged in a shorter period than those of the mid-season species. When profiles for the three groups are shown separately they show a regular outline...

S G Goodwin

Papers

Seasonal phenology and abundance of early-, mid- and long-season bumble bees in southern England, 1985–1989