The ecology and conservation of endangered saproxylic hoverflies (Diptera, Syrphidae) in Scotland

Hoverflies are important for their roles in ecological and environmental services, and are also charismatic species of conservation interest in their own right. Almost half of all hoverflies are saprophages, which are organisms that feed on dead or decaying organic matter, and these include saproxylic species that depend on deadwood. Deadwood and its associated community are a rich source of forest biodiversity and are fundamental to forest function, but due to poor management, many saproxylics are threatened or endangered, and techniques for conserving saproxylic species are poorly developed. In this thesis I study the ecology and conservation management of an endangered UK saproxylic fly, the Pine hoverfly, Blera fallax (Linnaeus) (Diptera, Syrphidae) and the dispersal ability of the similarly endangered Aspen hoverfly, Hammerschmidtia ferruginea (Fallén) (Diptera, Syrphidae). My main goals were to clarify methods to support their recovery in active programmes of species conservation in Scotland, UK. For B. fallax, this included experimenting with habitat creation techniques, investigating the best conditions for larval growth and assessing competition effects. In addition, I evaluated the genetic variability of the remaining population in Scotland by comparing it with one in Europe to determine whether genetic constraints may limit recovery. For H. ferruginea, I determined dispersal ability with field experiments involving mark and recapture techniques. By cutting holes at the surface of stumps of Pinus sylvestris, breeding habitat was created artificially for B. fallax at the remaining known locality for this species in the UK. Over 4 years, 81 % of holes were colonized by B. fallax, and by up to six other saproxylic syrphid species. The most successful holes were those cut into the heartwood, seeded with pine chips and sawdust and partially covered, as indicated by a combination of field occupancy monitoring and lab growth experiments. Observations of larval morphology and behaviour within rot holes revealed specializations that largely segregate the species in both time and space, and may mitigate interspecific competition between B. fallax and three more common syrphid species. I further demonstrated that B. fallax has a life history that features facultative semivoltine development, which may be a bet-hedging strategy to cope with fluctuating levels of larval food. Fifty B. fallax larvae were successfully reared and bred in captivity and from these, 430 descendent laboratory reared larvae and adults were released across three relocation sites. After initial success at the first re-location site when a new generation of larvae appeared in holes in 2010, a population crash at all sites occurred in the following year, possibly caused by adverse weather conditions. This disappointing result highlights the vulnerability of small populations to stochastic events, and means that survival of B. fallax may now depend on those larvae that are semivoltine, supplemented by animals currently being reared in captivity. My genetic analyses revealed similarly troubling information that highlights the precarious existence of B. fallax in Scotland: compared with a population in Sweden, Scottish B. fallax had significant less neutral genetic variation, and showed signs of a recent and severe bottleneck that reduced the effective population size to just 12 (CI: 0 - 266) individuals at some point in the last 200 years. Mindful of these challenges, I exploit my new data on the ecology and life history of B. fallax and combine it with techniques for captive rearing and for monitoring the genetic health of B. fallax into specific protocols and general prescriptions for the on-going recovery and management of this species. In order to assess the dispersal ability of H. ferruginea (and therefore its potential for recolonizing newly created habitat), in May to July over two years, adults were marked and released from a central point and subsequently monitored at the breeding site, decaying aspen wood Populus tremula, where adults tend to assemble for mating and oviposition. Adults were resighted visiting logs of decaying aspen set out at 1 km intervals along transects up to 7 km away. Up to 10 % of released individuals were resighted up to 5 km from the central release point. Most dispersing individuals (68 %) were resighted at 1 km, which I propose as the optimal distance for managing aspen for this species. Both of these hoverflies are case studies of techniques for recovering endangered saproxylic flies. Overall, my findings greatly increase fundamental knowledge of the ecology and natural history of these flies, and clarify some of the practical approaches that will be required in their conservation

Combined stress from parasites, pesticides and lack of flowers drives bee declines

Bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future

Investigating the foraging, guarding and drifting behaviors of commercial Bombus terrestris

Social insects have high levels of cooperation and division of labor. In bumble bees this is partly size-based, with larger bees performing tasks outside the nest and smaller bees remaining inside, although bumble bees still display considerable behavioral plasticity. The level of specialization in tasks outside the colony, including foraging, guarding and drifting (entering a foreign colony), is currently unknown for bumble bees. This study aimed to assess division of labor between outside tasks and the degree of specialization in foraging, guarding, and switching colonies in commercially reared bumble bees placed in the field. Nine factory-bought Bombus terrestris colonies were placed on three farms in Sussex, UK, between June and August 2015. Forty workers from each colony were radio-tagged and a reader on the colony entrance recorded the date, time and bee ID as they passed. The length and frequency of foraging trips and guarding behavior were calculated, and drifting recorded. The mean (±SD) length of foraging trips was 45 ± 36 min, and the mean number of foraging trips per day was 7.75 ± 7.71. Low levels of specialization in guarding or foraging behavior were found; however, some bees appeared to guard more frequently than others, and twenty bees were categorized as guards. Five bees appeared to exhibit repeated “stealing” behavior, which may have been a specialist task. The division of labor between tasks was not size-based. It is concluded that commercial bumble bees are flexible in performing outside nest tasks and may have diverse foraging strategies including intra-specific nest robbing

Monitoring neonicotinoid exposure for bees in rural and peri-urban areas of the UK during the transition from pre- to post-moratorium

Concerns regarding the impact of neonicotinoid exposure on bee populations recently led to an EU-wide moratorium on the use of certain neonicotinoids on flowering crops. Currently evidence regarding the impact, if any, the moratorium has had on bees’ exposure is limited. We sampled pollen and nectar from bumblebee colonies in rural and peri-urban habitats in three UK regions; Stirlingshire, Hertfordshire and Sussex. Colonies were sampled over three years; prior to the ban (2013), during the initial implementation when some seed-treated winter-sown oilseed rape was still grown (2014), and following the ban (2015). To compare species-level differences, in 2014 only, honeybee colonies in rural habitats were also sampled. Over half of all samples were found to be contaminated (n=408), with thiamethoxam being the compound detected at the highest concentrations in honeybee- (up to 2.29 ng/g in nectar in 2014, median≤0.1 ng/g, n=79) and bumblebee-collected pollen and nectar (up to 38.77 ng/g in pollen in 2013, median ≤0.12 ng/g, n=76). Honeybees were exposed to higher concentrations of neonicotinoids than bumblebees in 2014. While neonicotinoid exposure for rural bumblebees declined post-ban (2015), suggesting a positive impact of the moratorium, the risk of neonicotinoid exposure for bumblebees in peri-urban habitats remained largely the same between 2013 and 2015

Pollinator-flower interactions in gardens during the covid 19 pandemic lockdown of 2020

During the main COVID-19 global pandemic lockdown period of 2020 an impromptu set of pollination ecologists came together via social media and personal contacts to carry out standardised surveys of the flower visits and plants in gardens. The surveys involved 67 rural, suburban and urban gardens, of various sizes, ranging from 61.18° North in Norway to 37.96° South in Australia, resulting in a data set of 25,174 rows, with each row being a unique interaction record for that date/site/plant species, and comprising almost 47,000 visits to flowers, as well as records of flowers that were not visited by pollinators, for over 1,000 species and varieties belonging to more than 460 genera and 96 plant families. The more than 650 species of flower visitors belong to 12 orders of invertebrates and four of vertebrates. In this first publication from the project, we present a brief description of the data and make it freely available for any researchers to use in the future, the only restriction being that they cite this paper in the first instance. The data generated from these global surveys will provide scientific evidence to help us understand the role that private gardens (in urban, rural and suburban areas) can play in conserving insect pollinators and identify management actions to enhance their potential

The puparium and development site of Rhingia rostrata (Linnaeus) and comparison with R. campestris Meigen (Diptera, Syrphidae)

The puparium of Rhingia rostrata (Linnaeus) is described and compared with that of Rhingia campestris Meigen (Diptera, Syrphidae). Distinguishing characters for each species are recognised. A set of shared early stage characters that define the genus are proposed. Rhingia rostrata was reared from a hoverfly lagoon, an artificial development site, from which key features of natural development sites are suggested

Marvellous moths! pollen deposition rate of bramble (Rubus futicosus L. agg.) is greater at night than day

Widespread concerns about declines of wild pollinating insects has attracted considerable research interest, largely directed towards identifying key nectar sources and assessing the contribution of pollinators towards ecosystem services. However, previous work has almost exclusively focussed on bees and other diurnal invertebrate taxa. This study aimed to assess the relative contribution of diurnal and nocturnal insects to the pollination of bramble (Rubus fruticosus agg.), a common and widespread species aggregate across Europe, which has been identified as a key source of pollen and nectar for diurnal pollinators. Bramble flower visitation rates by diurnal and nocturnal insects were quantified by analysing over 380,000 interval photographs taken over a 3-day period across 10 sites. A pollinator exclusion experiment was also undertaken to assess the importance of diurnal and nocturnal insects for pollination by analysing pollen deposition on 480 bramble stigmas of nocturnally exposed, diurnally exposed and unvisited control flowers across all sites. Flower visitation was significantly higher during the day, comprising 83% of all visits made by a range of taxa. Nocturnal visitation was almost exclusively by moths. Crucially, pollen deposition rates of bramble were significantly higher during the night compared with the day. No relationship was detected between pollen counts and flower visitation rates, suggesting that moths are more efficient pollinators of bramble compared with diurnal insects. Overall, this work provides further evidence of the value of bramble as a resource for pollinators and demonstrates that moths likely play an important role in bramble pollination.</p

The aluminium content of each pupa from each colony.

<p>The aluminium content of each pupa from each colony.</p