Chris R. Shortall

Long-term phenological trends, species accumulation rates, aphid traits and climate: five decades of change in migrating aphids

1. Aphids represent a significant challenge to food production. The Rothamsted Insect Survey (RIS) runs a network of 12·2-m suction-traps throughout the year to collect migrating aphids. In 2014, the RIS celebrated its 50th anniversary. This paper marks that achievement with an extensive spatiotemporal analysis and the provision of the first British annotated checklist of aphids since 1964. 2. Our main aim was to elucidate mechanisms that advance aphid phenology under climate change and explain these using life-history traits. We then highlight emerging pests using accumulation patterns. 3. Linear and nonlinear mixed-effect models estimated the average rate of change per annum and effects of climate on annual counts, first and last flights and length of flight season since 1965. Two climate drivers were used: the accumulated day degrees above 16 °C (ADD16) indicated the potential for migration during the aphid season; the North Atlantic Oscillation (NAO) signalled the severity of the winter before migration took place. 4. All 55 species studied had earlier first flight trends at rate of β = −0·611 ± SE 0·015 days year−1. Of these species, 49% had earlier last flights, but the average species effect appeared relatively stationary (β = −0·010 ± SE 0·022 days year−1). Most species (85%) showed increasing duration of their flight season (β = 0·336 ± SE 0·026 days year−1), even though only 54% increased their log annual count (β = 0·002 ± SE <0·001 year−1). 5. The ADD16 and NAO were shown to drive patterns in aphid phenology in a spatiotemporal context. Early in the year when the first aphids were migrating, the effect of the winter NAO was highly significant. Further into the year, ADD16 was a strong predictor. Latitude had a near linear effect on first flights, whereas longitude produced a generally less-clear effect on all responses. Aphids that are anholocyclic (permanently parthenogenetic) or are monoecious (non-host-alternating) were advancing their phenology faster than those that were not. 6. Climate drives phenology and traits help explain how this takes place biologically. Phenology and trait ecology are critical to understanding the threat posed by emerging pests such as Myzus persicae nicotianae and Aphis fabae cirsiiacanthoidis, as revealed by the species accumulation analysis.

Developing and enhancing biodiversity monitoring programmes: a collaborative assessment of priorities

Summary Biodiversity is changing at unprecedented rates, and it is increasingly important that these changes are quantified through monitoring programmes. Previous recommendations for developing or enhancing these programmes focus either on the end goals, that is the intended use of the data, or on how these goals are achieved, for example through volunteer involvement in citizen science, but not both. These recommendations are rarely prioritized. We used a collaborative approach, involving 52 experts in biodiversity monitoring in the UK, to develop a list of attributes of relevance to any biodiversity monitoring programme and to order these attributes by their priority. We also ranked the attributes according to their importance in monitoring biodiversity in the UK. Experts involved included data users, funders, programme organizers and participants in data collection. They covered expertise in a wide range of taxa. We developed a final list of 25 attributes of biodiversity monitoring schemes, ordered from the most elemental (those essential for monitoring schemes; e.g. articulate the objectives and gain sufficient participants) to the most aspirational (e.g. electronic data capture in the field, reporting change annually). This ordered list is a practical framework which can be used to support the development of monitoring programmes. Peoples ranking of attributes revealed a difference between those who considered attributes with benefits to end users to be most important (e.g. people from governmental organizations) and those who considered attributes with greatest benefit to participants to be most important (e.g. people involved with volunteer biological recording schemes). This reveals a distinction between focussing on aims and the pragmatism in achieving those aims. Synthesis and applications. The ordered list of attributes developed in this study will assist in prioritizing resources to develop biodiversity monitoring programmes (including citizen science). The potential conflict between end users of data and participants in data collection that we discovered should be addressed by involving the diversity of stakeholders at all stages of programme development. This will maximize the chance of successfully achieving the goals of biodiversity monitoring programmes.

Long-term changes in the abundance of flying insects.

Abstract.  1. For the first time, long‐term changes in total aerial insect biomass have been estimated for a wide area of Southern Britain.

Escape from parasitism by the invasive alien ladybird, Harmonia axyridis

Alien species are often reported to perform better than functionally similar species native to the invaded range, resulting in high population densities, and a tendency to become invasive. The enemy release hypothesis (ERH) explains the success of invasive alien species (IAS) as a consequence of reduced mortality from natural enemies (predators, parasites and pathogens) compared with native species. The harlequin ladybird, Harmonia axyridis, a species alien to Britain, provides a model system for testing the ERH. Pupae of H. axyridis and the native ladybird Coccinella septempunctata were monitored for parasitism between 2008 and 2011, from populations across southern England in areas first invaded by H. axyridis between 2004 and 2009. In addition, a semi‐field experiment was established to investigate the incidence of parasitism of adult H. axyridis and C. septempunctata by Dinocampus coccinellae. Harmonia axyridis pupae were parasitised at a much lower rate than conspecifics in the native range, and both pupae and adults were parasitised at a considerably lower rate than C. septempunctata populations from the same place and time (H. axyridis: 1.67%; C. septempunctata: 18.02%) or in previous studies on Asian H. axyridis (2–7%). We found no evidence that the presence of H. axyridis affected the parasitism rate of C. septempunctata by D. coccinellae. Our results are consistent with the general prediction that the prevalence of natural enemies is lower for introduced species than for native species at early stages of invasion. This may partly explain why H. axyridis is such a successful IAS.

Ecological correlates of local extinction and colonisation in the British ladybird beetles (Coleoptera: Coccinellidae).

AbstractFive main drivers of population declines have been identified: climate change, habitat degradation, invasive alien species (IAS), overexploitation and pollution. Each of these drivers interacts with the others, and also with the intrinsic traits of individual species, to determine species’ distribution and range dynamics. We explored the relative importance of life-history and resource-use traits, climate, habitat, and the IAS Harmonia axyridis in driving local extinction and colonisation dynamics across 25 ladybird species (Coleoptera: Coccinellidae).Species were classified as continually present, continually absent, extinct, or colonising in each of 4,642 1-km2 grid squares. The spatial distribution of local extinction and colonisation events (in the grid squares) across all species’ ranges were related to ecological traits, overlap with H. axyridis, climate, and habitat factors within generalised linear models (GLMs). GLMs were also used to relate species’ traits, range characteristics, and niche overlap with H. axyridis to extinction and colonisation rates summarised at the species level. Bayesian model averaging was used to account for model uncertainty, and produce reduced sets of models which were well-supported by data. Species with a high degree of niche overlap with H. axyridis suffered higher extinction rates in both analyses, while at the spatial scale extinctions were more likely and colonisations less likely in areas with a high proportion of urban land cover. In the spatial analysis, polymorphic species with large range sizes were more likely to colonise and less likely to go extinct, and sunny grid squares were more likely to be colonised. Large, multivoltine species and rainy grid squares were less likely to colonise or be colonised. In conclusion for ladybirds, extinction and colonisation dynamics are influenced by several factors. The only factor that both increased the local extinction likelihood and reduced colonisation likelihood was urban land cover, while ecological overlap with H. axyridis greatly increased extinction rates. Continued spread of H. axyridis is likely to adversely affect native species and urban areas may be particularly vulnerable.

Large-scale migration synchrony between parasitoids and their host

1. Parasitoids are a valuable group for conservation biological control. In their role as regulators of aphid pests, it is critical that their lifecycle is synchronised with their hosts in both space and time. This is because a synchronised parasitoid community is more likely to strengthen the overall conservation biological control effect, thus damping aphid numbers and preventing potential outbreaks. One component of this host–parasitoid system was examined, that of migration, and the hypothesis that peak summer parasitoid and host migrations are synchronised in time was tested.

Mechanistic model for predicting the seasonal abundance of Culicoides biting midges and the impacts of insecticide control

BackgroundUnderstanding seasonal patterns of abundance of insect vectors is important for optimisation of control strategies of vector-borne diseases. Environmental drivers such as temperature, humidity and photoperiod influence vector abundance, but it is not generally known how these drivers combine to affect seasonal population dynamics.MethodsIn this paper, we derive and analyse a novel mechanistic stage-structured simulation model for Culicoides biting midges-the principle vectors of bluetongue and Schmallenberg viruses which cause mortality and morbidity in livestock and impact trade. We model variable life-history traits as functional forms that are dependent on environmental drivers, including air temperature, soil temperature and photoperiod. The model is fitted to Obsoletus group adult suction-trap data sampled daily at five locations throughout the UK for 2008.ResultsThe model predicts population dynamics that closely resemble UK field observations, including the characteristic biannual peaks of adult abundance. Using the model, we then investigate the effects of insecticide control, showing that control strategies focussing on the autumn peak of adult midge abundance have the highest impact in terms of population reduction in the autumn and averaged over the year. Conversely, control during the spring peak of adult abundance leads to adverse increases in adult abundance in the autumn peak.ConclusionsThe mechanisms of the biannual peaks of adult abundance, which are important features of midge seasonality in northern Europe and are key determinants of the risk of establishment and spread of midge-borne diseases, have been hypothesised over for many years. Our model suggests that the peaks correspond to two generations per year (bivoltine) are largely determined by pre-adult development. Furthermore, control strategies should focus on reducing the autumn peak since the immature stages are released from density-dependence regulation. We conclude that more extensive modelling of Culicoides biting midge populations in different geographical contexts will help to optimise control strategies and predictions of disease outbreaks.

The origins of global invasions of the German wasp (Vespula germanica) and its infection with four honey bee viruses

A successful control or eradication programme using biological control or genetically-mediated methods requires knowledge of the origin and the extent of wasp genetic diversity. Mitochondrial DNA variation in the native and invaded range of the social wasp Vespula germanica was used to examine intra-specific genetic variation and invasive source populations. We also examined wasps for the presence of four viruses found in honey bees: Acute bee paralysis virus, Deformed wing virus, Israeli acute paralysis virus and Kashmir bee virus. German wasps showed reduced genetic diversity in the invaded range compared to that of their native range. Populations in the introduced range are likely to have arrived from different source populations. All four viral honey bee pathogens were found in V. germanica, although they varied in their distribution and strain. Multiple introductions of German wasps have occurred for most invaded regions, though some populations are genetically homogenous. The differing locations of origin will guide researchers searching for biocontrol agents and the reduced genetic diversity may make these wasps a potentially viable target for control via gene drives.