Adult female gloomy scale with dorsal test removed and crawler emerging (10 units equal 1 mm). Photograph by Adam Dale.

Adult female gloomy scale with dorsal test removed and crawler emerging (10 units equal 1 mm). Photograph by Adam Dale.

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Gloomy scale, Melanaspis tenebricosa (Comstock), is native to the eastern United States and feeds on deciduous trees. In natural areas, it is a background herbivore that typically remains at low densities. Gloomy scale generally responds positively to warming with greater egg production, size, survival, and abundance. In urban areas, which are warm...

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... scale insect postembryonic development includes three instars for females and five for males (Beardsley andGonzalez 1975, Gullan andKosztarab 1997). Female and male first-instar gloomy scales (Fig. 4) are free moving with three pairs of legs, a pair of antennae, and a pair of eyes ( Metcalf 1922, Beardsley andGonzalez 1975). Crawlers are oval, cream to pale orange, and have an average length of 0.24 mm and width of 0.17 (Metcalf 1922). Upon settling on the host plant, gloomy scales tuck in their legs and antennae and begin ...

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... Research is needed to understand the correlation between elevation and OSS infestation, but temperature is a likely explanation. Fitness and abundance of other scale insect pests has been linked to climate (Frank 2020;Just et al. 2020), and low temperatures are known to reduce survival of overwintering OSS eggs (Tothill 1919). Therefore, colder temperatures at higher elevations might directly limit OSS. ...
... On the other hand, a warmer climate may have directly improved conditions for OSS population growth by increasing the species' fitness and abundance (Frank 2020;Frank and Just 2020). Because OSS appears to be limited to aspen stands below 2500 m (Table 1), cold temperatures may be a limiting factor for its spread, which is consistent with other scale insect pests (Frank 2020;Just et al. 2020) and OSS in other locations (Furniss and Carolin 1977). Temperature changes that have already occurred may have enabled OSS's spread outside urban areas Just et al. 2020), and in the future, warmer temperatures at higher elevations and latitudes may promote further spread of OSS (Frank 2020). ...
... Because OSS appears to be limited to aspen stands below 2500 m (Table 1), cold temperatures may be a limiting factor for its spread, which is consistent with other scale insect pests (Frank 2020;Just et al. 2020) and OSS in other locations (Furniss and Carolin 1977). Temperature changes that have already occurred may have enabled OSS's spread outside urban areas Just et al. 2020), and in the future, warmer temperatures at higher elevations and latitudes may promote further spread of OSS (Frank 2020). The former would threaten the largest, healthiest aspen stands in northern Arizona, which occur at higher elevations, and the latter would threaten the rest of aspen's range in the western US because Arizona is situated on the southwestern edge of the tree's range. ...
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Oystershell scale (OSS; Lepidosaphes ulmi) is an emerging invasive insect that poses a serious threat to conservation of quaking aspen (Populus tremuloides) in the southwestern US. Although OSS has been an urban pest in the US since the 1700s, it has recently spread into natural aspen stands in northern Arizona, where outbreaks are causing dieback and mortality. We quantified the ongoing outbreak of OSS at two scales: (1) local severity at two sites and (2) regional distribution across northern Arizona. Our regional survey indicated that OSS is widespread in lower elevation aspen stands and is particularly pervasive in ungulate exclosures. Advanced regeneration had the highest levels of infestation and mortality, which is concerning because this size class is an underrepresented component of aspen stands in northern Arizona. If OSS continues to spread and outbreaks result in dieback and mortality like we observed, then aspen in the southwestern US, and perhaps beyond, will be threatened. Three interacting factors contribute to OSS’s potential as a high-impact invasive insect that could spread rapidly: (1) its hypothesized role as a sleeper species, (2) potential interactions between OSS and climate change, and (3) the species’ polyphagous nature. Invasive pests like OSS pose an imminent threat to native tree species and, therefore, represent an immediate research and monitoring priority. We conclude with recommendations for future research and monitoring in order to understand OSS’s biology in natural aspen stands, quantify impacts, limit future spread, and mitigate mortality and loss of aspen and other host species.
Article
Warmer temperatures and frequent drought directly affect urban tree health. Both abiotic conditions also affect tree health via increased density of some insect pests. Warming is predicted to benefit urban trees by increasing carbon sequestration and allocation to biomass. However, increased drought and pests are rarely considered despite often co-occurring with heat. To determine the combined effects of these abiotic and biotic factors, we manipulated water availability for established urban red maple trees across a gradient of warming and pest density and measured leaf-level processes and tree growth over two years. We find that water availability is a major determinant of tree growth, physiological processes, and resilience to urban stress factors. Maples performed better with more water, which also made them resistant to effects of temperature and pest density. However, when drought became too severe, leaf-level processes declined with warming. Tree basal area growth was unaffected after two years, but stem elongation increased with increasing water, temperature, and pest density. We discuss potential mechanisms driving these responses and the implications in the context of urban forest management. Urban forest designs that reduce drought and align species adaptations to local conditions are critical for designing more resilient and productive urban forests.