Defoliation and dieback of Sitka spruce in Reykjavík, Iceland

The green spruce aphid Elatobium abietinum is an important defoliating pest of Sitka spruce (Picea sitchensis) in Iceland. A comparison of two urban Sitka stands in Reykjavík, from 2013-2017, reveals a distinct defoliation difference between trees located near a main road (94% defoliated) and several hundred meters away from heavy traffic (47%). Chemical analyses of the spruce needles demonstrate substantially higher nitrogen ratios in trees near traffic. Furthermore, the recently warming winter temperatures promoted larger overwintering aphid populations since 2003, as well as a shift of mass outbreaks from autumn to spring, accompanied by distinct growth suppressions one year after an aphid population spike in the post-2003 tree-ring data. The results of this study indicate that the mechanisms triggering Sitka spruce dieback in Reykjavík include a combination of increasing winter temperatures, more frequent and severe green spruce aphid outbreaks, as well as elevated N values in the needles of urban trees.

Stylostome formation by parasitic larvae of Allothrombium fuliginosum (Trombidiformes: Trombidiidae): morphology of feeding tubes and factors affecting their size

The morphology and formation of stylostomes (feeding tubes) in hosts’ body during the parasitic phase of Allothrombium fuliginosum (Hermann) larvae were studied for the first time with light microscopy (LM) and transmission electron microscopy (TEM). The stylostomes were observed in three aphids species—Acyrthosiphon pisum (Harris), Elatobium abietinum (Walker), and Macrosiphum rosae (L.)—parasitized by mites under laboratory conditions. They consisted of 2–6 main branches, preliminarily unbranched, then producing secondary and sometimes also tertiary branches as finally formed structures. Their walls were uniformly electron-dense, without any longitudinal and transverse stratifications and showed rather irregular outlines. Distally, the stylostome branches revealed transparent pores and cavities in their walls, connecting the stylostome canal with surrounding haemocoelic space. The total length of stylostomes at the end of the parasitic phase was on average 16× greater than that recorded in the youngest stylostomes. No differences in the overall shape of feeding tubes between host species were stated. The stylostomes formed in different host species did not differ significantly, except their total length, which attained the highest value in tissues of Ac. pisum.

Will warmer winters induce more forest and crop pests in Switzerland?

<p>Will warmer winters induce more forest and crop pests in Switzerland?</p><p>Léonard Schneider*,**</p><p>*Institute of Geography, University of Neuchatel, Espace Tilo-Frey 1, 2000 Neuchatel ([email protected])</p><p>**Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf</p><p> </p><p>With current global warming, recent winters have often been milder in Switzerland than they were in previous decades and should still become more so in the coming decades. Some insect species sensitive to winter extreme cold events could increase their survival rates during the cold season. Forest pests, such as pine processionary moth (Thaumetopoea pityocampa), green spruce aphid (Elatobium abietinum), and some crop pests, such as southern green stink bug (Nezara viridula), could overwinter more easily in Switzerland. These species are affected by temperatures below -12°C (Thaumetopoea pityocampa, Elatobium abietinum) to below -8°C (Nezara viridula).</p><p>This research aims to determine to what extent the evolution of winter minimum temperatures could increase the winter survival rate of some pest species in various places in Switzerland. We examine the trends for winter temperatures, with a special focus on cold events (days with minimal air temperature below -8°C and -12°C). We first analyse daily air temperature between 1980 and 2019 using 67 meteorological stations located all over Switzerland. Then, we use available data from CH2018 climatic scenarios to estimate possible trends along the coming century.</p><p>Preliminary results showed that the frequency of cold days has been decreasing in Switzerland over the last 40 years even though winter minimum temperatures have been increasing less than yearly minimum temperatures. By the end of the 21st Century, occurrences of temperatures below -12°C could become irregular up to 1700 m and winters with temperatures below -8°C could become rare at lower elevations in Switzerland. As a consequence, some crop pests such as southern green stin bug could overwinter more easily on the Swiss Plateau, and some forest pests such as green spruce aphid and pine processionary moth could reach higher elevations in mountain areas by the end of the century.</p>