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Order: Hempitera
Family: Diaspididae<\/p>\n
Unlike most insects, adult oystershell scales do not have legs, eyes, or antennae. Their appearance resembles a brown or grey oyster shell that is about 0.125 mm (1\/8 inch) long. When adult females die, they leave behind the waxy covering as a protective overwintering site for eggs. Newly hatched nymphs, called crawlers, are small, light yellow insects with functional legs for moving around bark. The crawlers are mobile for a short period of time before settling on bark to feed, at which point they begin secreting a waxy coating for protection. After molting, crawlers lose their legs, become immobile, and gradually increase in size over the following months. Adult females remain sessile for the rest of their life and as the insect matures, their armor increasingly resembles an oyster shell.<\/p>\n
[\/et_pb_text][et_pb_blurb title=”Quick Facts” use_icon=”on” font_icon=”||fa||900″ icon_color=”#F15625″ image_icon_width=”36px” _builder_version=”4.23.4″ _module_preset=”default” header_level=”h3″ header_font=”|||on|||||” header_text_align=”center” header_font_size=”26px” background_color=”#FEBD3B” custom_padding=”4%|4%|4%|4%|true|true” global_colors_info=”{}”]<\/p>\n
\u2022 The oystershell scale\u00a0is a scale insect that can be managed effectively with cultural and chemical controls.
\u2022 Of the scale insects in Colorado, the oystershell scale is the most damaging. It can attack a variety of trees and shrubs such as aspen, ash, cotoneaster, poplar, willow and lilac.
\u2022 Heavy scale infestations can increase plant susceptibility to pathogens. For example, cytospora fungi are frequently observed developing in areas previously infested with oystershell scales.<\/p>\n
[\/et_pb_blurb][et_pb_blurb image=”https:\/\/agsci.colostate.edu\/agbio\/wp-content\/uploads\/sites\/127\/2022\/08\/oystershell-scale-on-quaking-aspen.jpg” alt=”oystershell scale” _builder_version=”4.23.4″ _module_preset=”default” body_line_height=”1.4em” image_icon_custom_margin=”||-22px||false|false” custom_padding=”4%|4%|4%|4%|true|true” border_width_all=”4px” border_color_all=”#F15625″ global_colors_info=”{}”]<\/p>\n
Oystershell scale on quaking aspen. The oystershell scale is the most destructive scale insect in Colorado. Oystershell scales belong to a family of insects known commonly as armored scales and do not secrete honeydew. Oystershell scale infestations weaken plant defenses and make them more susceptible to pathogens. Outbreaks can be managed with a combination of biological, cultural, and chemical controls. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org<\/em><\/p>\n [\/et_pb_blurb][et_pb_blurb image=”https:\/\/agsci.colostate.edu\/agbio\/wp-content\/uploads\/sites\/127\/2022\/08\/oystershell-scale-flipped-eggs-exposed.jpg” alt=”oystershell scale eggs” _builder_version=”4.23.4″ _module_preset=”default” body_line_height=”1.4em” image_icon_custom_margin=”||-22px||false|false” global_colors_info=”{}”]<\/p>\n Oystershell scale flipped to expose the eggs. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org<\/em><\/p>\n [\/et_pb_blurb][\/et_pb_column][et_pb_column type=”1_2″ _builder_version=”4.16″ custom_padding=”|||” global_colors_info=”{}” custom_padding__hover=”|||”][et_pb_blurb image=”https:\/\/agsci.colostate.edu\/agbio\/wp-content\/uploads\/sites\/127\/2022\/08\/oystershell-scale-infestation.jpg” alt=”oystershell scale infestation” _builder_version=”4.23.4″ _module_preset=”default” body_line_height=”1.4em” image_icon_custom_margin=”||-22px||false|false” global_colors_info=”{}”]<\/p>\n Oystershell scale infestation. Infestations are generally confined to smaller portions of the tree. Image credit: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Bugwood.org<\/em><\/p>\n [\/et_pb_blurb][et_pb_blurb image=”https:\/\/agsci.colostate.edu\/agbio\/wp-content\/uploads\/sites\/127\/2022\/08\/bark-cracking-cause-oystershell-scale.jpg” alt=”bark cracking” _builder_version=”4.23.4″ _module_preset=”default” body_line_height=”1.4em” image_icon_custom_margin=”||-22px||false|false” global_colors_info=”{}”]<\/p>\n Bark cracking on aspen due to a previous oystershell scale infestation. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org<\/em><\/p>\n [\/et_pb_blurb][et_pb_blurb image=”https:\/\/agsci.colostate.edu\/agbio\/wp-content\/uploads\/sites\/127\/2022\/08\/cytospora-fruiting-bodies-oystershell-scale.jpg” alt=”cytospora fruiting bodies” _builder_version=”4.21.0″ _module_preset=”default” body_line_height=”1.4em” image_icon_custom_margin=”||-22px||false|false” global_colors_info=”{}”]<\/p>\n Cytospora fruiting bodies growing in areas previously damaged by ostershell scales. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org<\/em><\/p>\n [\/et_pb_blurb][et_pb_blurb image=”https:\/\/agsci.colostate.edu\/agbio\/wp-content\/uploads\/sites\/127\/2022\/08\/removing-oystershell-scale.jpg” alt=”removing oystershell scale” _builder_version=”4.23.4″ _module_preset=”default” body_line_height=”1.4em” image_icon_custom_margin=”||-22px||false|false” global_colors_info=”{}”]<\/p>\n Removing oystershell scale from tree trunk using a scrub brush. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org<\/em><\/p>\n [\/et_pb_blurb][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.17.4″ _module_preset=”default” background_color=”#F1F1F1″ global_colors_info=”{}”][et_pb_row _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text admin_label=”Squiggle” _builder_version=”4.17.4″ _module_preset=”default” header_font=”||||||||” header_text_align=”left” header_font_size=”22px” custom_padding=”||||false|false” saved_tabs=”all” global_colors_info=”{}”]<\/p>\n\t\t [\/et_pb_text][et_pb_text _builder_version=”4.23.4″ _module_preset=”default” header_2_font_size=”36px” header_3_font_size=”26px” global_colors_info=”{}”]<\/p>\n All scale insects undergo incomplete metamorphosis and have three life stages: egg, nymph, adult. Scale insects can be divided into two categories, the armored scales (family: Diaspididae), that produce armor that is not attached to the insect\u2019s body, and soft scales (family: Coccidae), that produce armor that remains attached to the body of the insect. This pest is classified as an armored scale. Females lay eggs in late summer and early fall and die at the end of the season. Eggs overwinter under the mother scale\u2019s old armor (see image) and hatch over a period of 2-3 weeks in late May or early June. Crawlers are highly susceptible to certain controls because they are small and do not have a waxy protective cover like adults. Crawlers can also disperse by wind or tree dwelling animals like birds and squirrels as they move from one tree to another, and those that do not successfully find a feeding site within a few days after hatching will die. By midsummer they are fully mature adults. So far, no male oystershell scales had been observed in Colorado; regional oystershell populations are believed to reproduce asexually with one generation produced per year.<\/p>\n Surveys have indicated that this pest is widespread in aspen stands at lower elevations, and outbreaks of oystershell scale pose a significant threat to quaking aspen (Populus tremuloides<\/em>) in northern Arizona, which is a widely distributed keystone species in the conifer-dominated forests of the western United States. This polyphagous scale insect has also significantly impacted stands of American beech (Fagus grandifolia<\/em>) and ash (Fraxinus spp<\/em>.) in the eastern United States.<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_row _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_text admin_label=”Squiggle” _builder_version=”4.17.4″ _module_preset=”default” header_font=”||||||||” header_text_align=”left” header_font_size=”22px” custom_padding=”||||false|false” saved_tabs=”all” locked=”off” global_colors_info=”{}”]<\/p>\n\t\t [\/et_pb_text][et_pb_text _builder_version=”4.24.2″ _module_preset=”default” header_3_font_size=”26px” global_colors_info=”{}”]<\/p>\n All scale insects have piercing-sucking mouthparts that extract fluids from the plant. It is common to observe dieback of twigs or branches on trees infested with oystershell scales. Reduced leaf size and chlorosis (yellowing) of leaves is another commonly observed symptom. Without effective management, severe infestations can kill trees or shrubs.<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.18.0″ _module_preset=”default” background_color=”#F1F1F1″ global_colors_info=”{}”][et_pb_row _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_text admin_label=”Squiggle” _builder_version=”4.17.4″ _module_preset=”default” header_font=”||||||||” header_text_align=”left” header_font_size=”22px” custom_padding=”||||false|false” saved_tabs=”all” locked=”off” global_colors_info=”{}”]<\/p>\n\t\t [\/et_pb_text][et_pb_text _builder_version=”4.24.2″ _module_preset=”default” header_3_font_size=”26px” global_colors_info=”{}”]<\/p>\n Crawlers are the most vulnerable life stage of oystershell scale because they are small and do not have a waxy protective cover. There are many insecticides that can be used to control this pest when applied during the egg hatch\/crawler migration period. However, timing is important because these insects become much less susceptible to most insecticides after the waxy cover begins to develop.<\/p>\n Monitoring for crawler activity can be done in two ways. The first involves wrapping double sided sticky tape around infested twigs in mid-May. Use a magnifying lens to check the tape every other day for crawlers. The other monitoring strategy involves gently shaking or tapping branches over a piece of white paper or a white tray. The fallen debris can then be examined for crawlers with a magnifying lens.<\/p>\n It is important to note that old scales can remain in place several years even after death. Clear old scales from the branch to allow for detection of new infestations. Old dead scales will be dry and flaky, while scales containing eggs will be moist when crushed.<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.23.4″ _module_preset=”default” background_color=”#FFFFFF” global_colors_info=”{}”][et_pb_row _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_text admin_label=”Squiggle” _builder_version=”4.17.4″ _module_preset=”default” header_font=”||||||||” header_text_align=”left” header_font_size=”22px” custom_padding=”||||false|false” saved_tabs=”all” locked=”off” global_colors_info=”{}”]<\/p>\n\t\t [\/et_pb_text][et_pb_text _builder_version=”4.24.2″ _module_preset=”default” header_3_font_size=”26px” global_colors_info=”{}”]<\/p>\n In small aspen enclosures with short trees, a strong jet of water can be used to dislodge crawlers. Eggs and old scale coverings can be removed and destroyed by using a soft plastic brush to scrub the bark, although branches that are heavily infested may need to be pruned. In large aspen enclosures with encroaching coniferous trees, removing competing vegetation and sanitizing infested materials is recommended. Sanitation can be accomplished by piling and burning infested materials collected from aspen in the spring when soils are moist. Piles of infested materials should be placed a minimum of 61 m (200 feet) downwind of the aspen stand to help prevent infestations from wind-dispersed crawlers.<\/p>\n The presence of very few non-infested stems indicates that a severe infestation is present. In this instance, sanitation can help trees recover from infestation. It is recommended that such measures be followed with insecticide applications to target crawlers.<\/p>\n There are few natural enemies of oystershell scale in Colorado. Predatory mites have been observed feeding on overwintering oystershell scale eggs. While there are parasitic wasps in Colorado, they are not typically associated with oystershell scales.<\/p>\n Horticultural oils display low toxicity toward non-target organisms and work by smothering insects or mites on plants, making them effective tools in oystershell scale management. Those applied during the plant\u2019s dormant period are called dormant oils and target overwintering oystershell scale eggs. It is important to note that other controls may also be necessary to treat heavy outbreaks. More information on horticultural oils is available here<\/a>.<\/p>\n Insecticidal soaps use potassium salts to control armored scales and a wide variety of other insect pests. The active ingredient rapidly breaks down and does not persist in the environment after being sprayed directly on bark, limbs, and stems. However, insecticidal soaps should not be applied to drought-stressed plants, and several applications may be required and supplemented with other control measures. It is important to note that insecticidal soaps are hazardous to humans and domestic animals when misused. These products should not be used near water bodies as they are also toxic toward aquatic invertebrates.<\/p>\n Insecticide applications are most effective against the crawler stage before they settle down and form a waxy coating. Using the monitoring methods described above, plants should be examined to determine the crawler period before applying insecticides since seasonal timing varies due to spring weather conditions. Some effective insecticides against the oystershell scale include insect growth regulators like buprofezin or pyriproxifen, or systemic insecticides such as dinotefuran applied as soil drench or bole\/stem sprays. In addition, a single application of carbaryl can protect susceptible trees throughout the emergence period. Monitoring should continue after the insecticide application to evaluate its efficacy. While crawlers can be killed with most insecticides, the most effective chemical controls are those with persistent activity since eggs hatch over time. For more information on chemical control options for oystershell scale, visit the full factsheet<\/a>.<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.23.4″ _module_preset=”default” background_color=”#F1F1F1″ global_colors_info=”{}”][et_pb_row _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.17.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_blurb title=”CSU Extension Fact Sheet” url=”https:\/\/extension.colostate.edu\/topic-areas\/insects\/oystershell-scale-5-513\/#:~:text=The%20oystershell%20scale%2C%20Lepidosaphes%20ulmi,%2C%20poplars%2C%20willow%20and%20lilac.” use_icon=”on” font_icon=”||fa||900″ icon_color=”#F15625″ image_icon_width=”36px” _builder_version=”4.18.0″ _module_preset=”default” header_level=”h2″ header_font_size=”36px” locked=”off” global_colors_info=”{}”]<\/p>\n Download or view the CSU Extension’s PDF fact sheet for your reference.<\/p>\n [\/et_pb_blurb][et_pb_text admin_label=”Squiggle” _builder_version=”4.17.4″ _module_preset=”default” header_font=”||||||||” header_text_align=”left” header_font_size=”22px” custom_padding=”||||false|false” saved_tabs=”all” locked=”off” global_colors_info=”{}”]<\/p>\n\t\t [\/et_pb_text][et_pb_text _builder_version=”4.24.2″ _module_preset=”default” header_3_font_size=”26px” hover_enabled=”0″ global_colors_info=”{}” sticky_enabled=”0″]<\/p>\n Connor, C. et al. 2021.<\/strong> Oystershell scale: an emerging invasive threat to aspen in the southwestern US. Biological Invasions. 23(9): 2893-2912. Available https:\/\/link.springer.com\/content\/pdf\/10.1007\/s10530-021-02545-0.pdf<\/a><\/p>\n Grady, A. 2017.<\/strong> Oystershell Scale Impacts and Mitigation Options on the Kaibab and Coconino NF\u2019s. United States Forest Service \u2013 Department of Agriculture. Forest Health Protection Report. Available https:\/\/digitalcommons.usu.edu\/cgi\/viewcontent.cgi?article=8652&context=aspen_bib<\/a><\/p>\n Held, D. 2019.<\/strong> Controlling Scale Insects and Mealybugs. Alabama A & M and Auburn Universities: Cooperative Extension. Available https:\/\/www.aces.edu\/blog\/topics\/lawn-garden\/controlling-scale-insects-and-mealybugs\/<\/a><\/p>\n Hoover, G. 2003.<\/strong> Oystershell Scale. Penn State: Extension. Available https:\/\/extension.psu.edu\/oystershell-scale#:~:text=Damage,infestation%20of%20this%20insect%20occurs.<\/a><\/p>\n Karren, J., and A. Roe. 2019.<\/strong> Oystershell (Mussel) Scale (Lepidosaphes ulmi). Utah State University \u2013 Extension. Available https:\/\/digitalcommons.usu.edu\/cgi\/viewcontent.cgi?article=2358&context=extension_curall<\/a><\/p>\nLife history and habits<\/h2>\n
Injury<\/h2>\n
Monitoring<\/h2>\n
Cultural control<\/h2>\n
Biological control<\/h2>\n
Chemical control<\/h2>\n
References<\/h2>\n