Hamish A. Symington

Cuckoo bumblebees must successfully locate and invade a colony of their host bumblebee species to achieve reproductive success. Past work has established the role of non‐visual cues in guiding cuckoo bumblebee host‐finding behaviour. However, a majority of these studies have used chemical extracts from host bumblebees rather than colonies that resemble what the cuckoo bumblebee would encounter in natural conditions. To further understand the role of non‐visual cues guiding cuckoo bumblebees and to quantify the accuracy with which cuckoo bumblebees find their hosts, we conducted a series of choice experiments with wild‐caught cuckoo bumblebees Bombus vestalis Geoffroy, 1785 and small lab‐reared colonies of their host, Bombus terrestris Linnaeus, 1758. Wild‐caught female cuckoo bumblebees were introduced to a flight arena containing four identical opaque boxes, each of which featured slits to release volatiles from bumblebees placed within. When only one box contained a small host colony, the cuckoo bumblebees were able to locate their hosts among the four boxes with 66.2% accuracy. When B. terrestris brood, workers and the queen were placed in separate opaque boxes, the cuckoo bumblebees did not show a clear preference among them but still avoided an empty control box. This is an initial step in understanding the accuracy of host detection in cuckoo bumblebees and the components of a colony attracting invasion.

Analysis of floral nectar reward often involves converting nectar volume to sugar mass. Nectar density depends on nectar sugar concentration, and has been empirically measured. A quadratic equation which accurately models sucrose density over a range of concentrations was published in a book in 1987. This equation was restated in a publication in 2001, but with a typographical error transposing two digits in the coefficient of the linear term. The incorrect equation has been used in numerous studies since its publication, including in the generation of large datasets. However, the error in density introduced by the incorrect equation is never more than 0.5%, which is greatly smaller than the standard deviation in published floral measurements of nectar volumes and concentrations. The error is therefore likely to have limited consequences, but we recommend using the more accurate equation for future studies. While exploring this error we found several others, some of which affect reported data and some of which are simple typographical errors introduced while preparing a manuscript. We caution authors to be scrupulous in reporting units and equations relating to nectar measurement.

A rising global population will need more food, increasing demand for insect pollination services. However, general insect declines conflict with this demand. One way to mitigate this conflict is to grow crop flowers that are easier for insects to find and more rewarding to those that visit them. This study quantifies variation in the pollinator‐relevant traits of nectar and pollen production, flower size and flower shape in commercial strawberry, finding significant variation between varieties in all traits. Bumblebees could learn to distinguish between the extremes of variation in flower shape, but this learning is very slow, indicating that this variation is at the limit of that which can be detected by bumblebees. Bee preferences for nectar of differing sugar concentrations at field‐realistic volumes were consistent with previous observations at larger volumes, suggesting that it is valid to translate lab findings to the field. This study builds on our knowledge of the range of pollinator reward present in a single cultivated species and of the impact of field‐realistic levels of variation in floral traits on bumblebee preferences.

Nectar is a common reward provided by plants for pollinators. More concentrated nectar is more rewarding, but also more viscous, and hence more time-consuming to drink. Consequently, theory predicts an optimum concentration for maximizing energy uptake rate, dependent on the mechanics of feeding. For social pollinators such as bumblebees, another important but little-studied aspect of foraging is nectar offloading upon return to the nest. Studying the bumblebeeBombus terrestris, we found that the relationship between viscosity (µ) and volumetric transfer rates (Q) of sucrose solutions differed between drinking and offloading. For drinking,Q∝µ^−0.180, in good agreement with previous work. Although offloading was quicker than drinking, offloading rate decreased faster with viscosity, withQ∝µ^−0.502, consistent with constraints imposed by fluid flow through a tube. The difference in mechanics between drinking and offloading nectar leads to a conflict in the optimum concentration for maximizing energy transfer rates. Building a model of foraging energetics, we show that including offloading lowers the maximum rate of energy return to the nest and reduces the concentration which maximizes this rate by around 3%. Using our model, we show that published values of preferred nectar sugar concentrations suggest that bumblebees maximize the overall energy return rather than the instantaneous energy uptake during drinking.

We discuss the suggestion that differences in the nucleotide composition between plastid and nuclear genomes may provide a selective advantage in the transposition of genes from plastid to nucleus. We show that in the adenine, thymine (AT)–rich genome of Borrelia burgdorferi several genes have an AT–content lower than the average for the genome as a whole. However, genes whose plant homologues have moved from plastid to nucleus are no less AT–rich than genes whose plant homologues have remained in the plastid, indicating that both classes of gene are able to support a high AT–content. We describe the anomalous organization of dinoflagellate plastid genes. These are located on small circles of 2–3 kbp, in contrast to the usual plastid genome organization of a single large circle of 100–200 kbp. Most circles contain a single gene. Some circles contain two genes and some contain none. Dinoflagellate plastids have retained far fewer genes than other plastids. We discuss a similarity between the dinoflagellate minicircles and the bacterial integron system.

We show using PCR that psbC, atpA and petB genes are present in the plastid DNA minicircles from the dinoflagellate Amphidinium operculatum, extending the set of plastid genes identified from this organism. Unusually, the petB and atpA genes are located on the same minicircle. PCR using primers based on the "core" region found on all coding minicircles revealed the existence of a number of DNA minicircles with no apparent coding function. Northern analysis of total RNA from A. operculatum showed that the petB and atpA genes are represented on separate transcripts, despite being encoded in close proximity on the same minicircle. The possibility of transcript editing was investigated by RT-PCR, but psaA, psbA, psbB and atpB transcripts showed no evidence of editing, indicating that GUA can be used as an initiation codon in A. operculatum.