Scale Insects

Scale insects belong to the family Coccidae, which is a large and diverse group about 8,000 insects. The family Coccidae is part of the order Hemiptera, which also includes other pests such as aphids, whiteflies, and stink bugs.

Host Plants

Scale insects can infest a wide range of plants, including both woody and herbaceous species. Some common host plants include:

• Fruit trees: They are a common problem on citrus trees, as well as other fruit trees such as apples, peaches, and pears.
• Ornamental trees and shrubs: They can infest popular ornamental trees and shrubs such as camellias, hollies, magnolias, and oleanders.
• Houseplants: Many common houseplants, including ficus, jade plants, and hibiscus.
• Vines: They can infest climbing plants such as grapes and English ivy.
• Agricultural crops: They can cause damage to a wide range of crops, including cotton, soybeans, and sugarcane.

It’s important to note that the specific types of scale insects that infest a particular host plant can vary depending on the location and climate. In addition, different species may have different preferences for certain types of plants, so it’s important to correctly identify the species of scale insect present to determine the most appropriate control measures.

Regions impacted

Scale insects are found throughout the world.

Different species are native to different regions, and some species have been introduced to new areas through human activities such as trade and agriculture.

In general, scale insects thrive in warm, moist climates but can also be found in more temperate regions. The specific types of scale insects found in a particular region can vary depending on the local climate, host plants, and the presence of natural enemies such as predators and parasites.

Description

Scale insects are small, sap-sucking insects characterized by a protective covering, or “scale,” on their body, ranging from a hard, shell-like covering to a soft, wax-like covering.

The scale covering protects the insect and can make it difficult to control with insecticides.

There are several types of scale insects, including armored scales, soft scales, and mealybugs. Each type is characterized by a different type of protective covering, and different species may have different preferences for host plants.

• Armored scale insects: They have a hard, protective covering that protects them from predators and insecticides. This type of scale insect does not produce honeydew and is often more difficult to control. Examples include the San Jose scale and the oyster shell scale.
• Soft scale insects: They have a soft, waxy covering that protects them from predators and insecticides. This type of scale insect produces honeydew, which can attract ants and promote the growth of sooty mold on the plant’s leaves and branches. Examples include the cottony cushion scale and the giant whitefly.
• Mealybugs: Mealybugs are a type of scale insect that have a soft, waxy covering and produce honeydew. They are often found in clusters on the plant and can cause significant damage to the plant if not controlled. Examples of mealybugs include the citrus mealybug and the long-tailed mealybug.

Life Cycle

The life cycle consists of several stages, including egg, nymph, and adult. The specific details of the life cycle can vary depending on the species of scale insect, but the general pattern is as follows:

• Egg: Females lay their eggs under their protective covering or “scale.” The eggs are usually small and white and can be laid in large numbers.
• Nymph: The eggs hatch into nymphs, also called “crawlers.” The nymphs are the active stage of the insect, and they move around in search of a suitable feeding site. Once they find a suitable location, they insert their mouthparts into the plant and feed on plant fluids.
• Adult: After feeding for some time, the nymphs molt into the adult stage, usually characterized by a hard, protective covering. Male insects usually have wings and can fly, while females are usually flightless. Males mate with females, and females lay eggs to begin the cycle anew.

The life cycle can take a few weeks to several months, depending on the species and the environmental conditions. The life cycle may occur more quickly in warmer climates, allowing multiple generations of scale insects to occur in a single growing season.

Damage and Detection

Scale insects can cause significant damage to crops, ornamental plants, and trees. They feed on plant fluids, causing leaf yellowing, stunted growth, wilting, and, in severe infestations, plant death. Scale insects can also secrete a sticky, sugary substance known as honeydew, which can attract ants and promote the growth of sooty mold on the plant’s leaves and branches.

Detecting scale insects can be challenging, as their protective covering can make them difficult to see. However, several signs can indicate their presence:

• Sticky residue: The presence of honeydew and sooty mold on the plant’s leaves and branches is a sign that these insects may be present.
• Yellowing leaves: They can cause the yellowing of leaves, which may be a sign of damage.
• Stunted growth: Scale insects can cause stunted growth, which may indicate that the plant is not getting enough nutrients.
• Wilting: These insects can cause wilting, which may indicate that the plant is not getting enough water.
• Presence of scales: The protective covering, or “scale,” on the plant is a sign that these insects may be present.

Prevention and Control

There are several methods for controlling scale insects, including chemical control, biological control, and cultural control. The most appropriate control measures will depend on the type of scale insect present and the severity of the infestation. Here are some common methods for controlling them:

• Biological control: Introducing natural predators, such as ladybugs, lacewings, soldier beetles, and parasitic wasps, can help to control scale insects. These predators feed on these insects, helping to reduce their populations.
• Cultural control: Maintaining plant health and promoting natural predators can also effectively control scale insects. This can be achieved by providing adequate water and nutrients, avoiding stress on the plant, and promoting good air circulation.
• Physical control: For small infestations, physically removing these insects by hand can be effective. For example, you can scrape the insects off the plant with a fingernail or a soft brush.

Horticultural oils and soaps: Horticultural oils and soaps can help to control these insects by smothering them or disrupting their ability to feed. These products are generally safe for plants and beneficial insects and can be applied directly to the plant.

• Neem oil: Neem oil is a natural, plant-based insecticide that can effectively control these insects. It disrupts insects’ feeding and reproduction and is generally safe for plants and beneficial insects.
• Chemical control: Chemical insecticides can effectively control these insects. However, it’s important to choose the right product for the type of scale insect present and to follow the label instructions carefully. Chemical control should be used as a last resort, as it can also harm beneficial insects such as ladybugs, lacewings, and parasitic wasps.

It’s important to monitor plants for the presence of scale insects and to control infestations as soon as possible to prevent significant damage to the plant. If you have questions or concerns about these insects on your plants, it is best to consult with a local horticulturist or agricultural extension office for specific recommendations for your area.