Research
Green spruce aphid (Elatobium abietinum) research
Research Status:current
This page briefly describes the recent research that Forest Research has conducted on the green spruce aphid (Elatobium abietinum).
Green spruce aphids are an important defoliating pest of Sitka spruce (Picea sitchensis) that may become more damaging in the future as a result of climate change. The severity of defoliation by green spruce aphid within a given year is determined by its maximum population size. These vary widely from year-to-year, in response to winter and spring temperatures and a strong negative feedback response to the aphid population in the previous year. This means that a high population and high defoliation year, will be followed by at least one or two years of recovery as the population will have dipped in response to predator pressure before another peak year can occur.
For more information on the life cycle and symptoms of spruce aphid infestation, please visit our green spruce aphid biology resource page.
2019: Effects of high temperatures on individuals and populations of green spruce aphid.
Mild winters and higher spring temperatures increase green spruce aphid population densities, although this positive response to warmer conditions might be over-ridden if green spruce aphids are adversely affected by exceptionally high summer temperatures. This project aims to compare increasing temperature vs survival of green spruce aphids in both laboratory and field settings.
Specific research objectives are to analyse datasets collected during field studies in Wales and laboratory experiments to:
In laboratory experiments, aphids exposed to temperatures above 25oC became more restless and were more likely to drop from the shoot, and subsequently showed a reduction in mean relative growth rate. In contrast, survival was not reduced significantly unless temperatures exceeded 35oC.
Data was analysed from a field experiment carried out from 1999-2006 at Radnor Forest in mid-Wales. The field data indicated that green spruce aphid populations in the autumn were inversely correlated with mean and maximum summer temperatures, at temperatures below those that had a negative impact in the laboratory. The greater sensitivity of populations in the field to high summer temperatures may reflect higher temperatures at the needle surface compared with the temperature of the surrounding air, or associated increases in natural enemy activity.
The results from the present study indicate that high temperatures during mid-summer have a significant impact on green spruce aphid individuals and populations and, ultimately, may influence how the aphid responds to climate change.
2017: The influence of forest management on the abundance and diversity of hoverflies in commercial plantations of Sitka spruce: the importance of sampling in the canopy.
This project aims to compare abundance, species richness and diversity of hoverflies (Diptera: Syrphidae) inhabiting spruce forests that have been managed using alternative silvicultural systems. The project tests the hypothesis that increasing the structural complexity of forest stands will increase the diversity of aphidophagous predator invertebrate species, and thus reduce the impact of green spruce aphid on Sitka spruce trees.
Specific research objectives are to analyse datasets collected during field studies in Wales, to:
Hoverflies were sampled in 5 shelterwood stands, 6 group selection stands and 13 even-aged stands of Sitka spruce at 4 forest sites in mid and north Wales. Sampling took place at ground level and in the canopy, using yellow pan traps and flight interception traps. 7323 adult hoverflies of 74 species were captured, the majority of these in traps in the canopy.
Total hoverfly abundance and the abundance of aphidophagous species were significantly higher (P < 0.001) in group selection stands. The lowest abundance was recorded in even-aged stands, but patterns in abundance amongst the even-aged stands depended on whether sampling was carried out near the ground or in the canopy.
Traps at ground level caught significantly fewer hoverflies in mid-rotation even-aged stands, whereas traps in the canopy caught similar, if not more, hoverflies in mid-rotation stands compared with young and mature even-aged stands.
Stand species richness was closely related to the total numbers of individuals captured (abundance) and as a result was also highest in group selection stands, but there was no fundamental difference in hoverfly diversity (H’) between stand types or silvicultural systems.
The data indicates that unlike abundance, overall hoverfly diversity was determined at a wider landscape scale. At the plot scale, there was no evidence that structurally complex spruce stands supported more species because they provided a wider range of microhabitats and ecological niches.
2011: Defoliation and growth relationships for mid-rotation Sitka spruce attacked by the green spruce aphid
This project aims to compare populations of the green spruce aphid inhabiting spruce forests that have been managed using alternative silvicultural systems. The project tests the hypothesis that increasing the structural diversity of forest stands can reduce the impact of pest species, in particular by supporting a greater diversity and abundance of invertebrate natural enemies.
Specific research objectives are to analyse datasets collected during field studies in Wales, to:
Green spruce aphids and invertebrate natural enemies were sampled in 24 Sitka spruce stands in Wales from 2007 to 2011, using a variety of techniques at ground level and in the canopy. Preliminary analyses show that green spruce aphid densities increased with tree age in even-aged stands, but on average were higher in group selection and shelterwood stands. Aphid densities above 2.8 aphids per 100 needles reduce volume increment of Sitka spruce by 6% (Straw et al., 2011) and this threshold was exceeded in mid and mature even-aged stands and on trees of all ages in the mixed-age stands.
Invertebrate predators showed a wide range of responses to forest management and stand structure. Amongst the even-aged stands, some taxa, notably lacewings (Hemerobiidae) and smaller soldier beetles (Malthodes, Cantharidae) increased in abundance with stand age and attained their highest densities in mature stands, in a manner similar to the increase in green spruce aphid populations. Other predators however, such as ladybirds (Coccinellidae), hoverfly larvae (Syrphidae) and the larger soldier beetles (Rhagonycha, Cantharidae) decreased in abundance in the oldest stands and attained maximum population densities in mid-rotation stands. Populations of natural enemies in group-selection and shelterwood stands were either similar to or lower than those observed in even-aged stands.
Straw, N. A., Bladon, F. M., Day, K. R., & Fielding, N. J. (2019). The effects of high temperatures on individuals and populations of the green spruce aphid Elatobium abietinum (Walker). Agricultural and Forest Entomology, 21(1), 69-78.
Straw, N. A., Williams, D. T., Fielding, N. J., Jukes, M., Connolly, T., & Forster, J. (2017). The influence of forest management on the abundance and diversity of hoverflies in commercial plantations of Sitka spruce: the importance of sampling in the canopy. Forest Ecology and Management, 406, 95-111.
Straw, N.A., Fielding, N., Green, G., Price, J. & Williams, D. (2011) Defoliation and growth relationships for mid-rotation Sitka spruce attacked by the green spruce aphid, Elatobium abietinum (Walker) (Homoptera: Aphididae). Forest Ecology and Management 262, 1223–1235.
This research is funded by the Forestry Commission under the programme, Advice and Scientific Support for Tree Health.
This research underpins the evidence base for the delivery of healthy and resilient forests and wider ecosystems which is part of the Tree Health and Plant Biosecurity Action Plan.
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