Scales are sucking insects that insert their tiny, straw-like mouthparts into bark, fruit, or leaves, mostly on trees and shrubs and other perennial plants. Some scales can seriously damage their host, while other species do no apparent damage to plants even when scales are very abundant. The presence of scales can be easily overlooked, in part because they do not resemble most other insects.
Lecanium scales in the picture above (there are about 12 species) are known as “soft” scales and are common pests on many ornamental plants all over North America. Holly, elm, redbud, walnut, citrus, apricot, pear, persimmon, beech, box elder, grape, pecan, rose, and willow are a sample of the diverse range of hosts that Lecanium scales can parasitize.
As these scales feed, they excrete large quantities of honeydew which serves as a substrate for sooty mold fungi.
Here is a link to a previous post I wrote about this scale on pecan. Scale on Pecan?
- San Jose Bark Scale
- Crape Myrtle Bark Scale
- Mealybugs are prominent now in Greenhouses and Houseplants
- Introduction of Natural Predators or Disease
San Jose Bark Scale
Photo by C. L. Cole.
San Jose Bark Scale is one of the major insect pest of peaches and maybe one that causes the most damage. The first signs of infestation include a decline of tree vigor, leaf drop and appearance of sparse yellow foliage, particularly on the terminal growth. Reddish spots on the underside of bark and around scales on leaves or fruit result from feeding of immature stages. In severe cases, the entire surface of bark can become covered with layers of overlapping grayish scales. Cracking and bleeding of limbs occur and heavily injured trees may die.
Life Cycle: Intermediate. Mature females and immature (second nymphal instar) stages survive the winter. Rather than eggs, female scale insects produce tiny six-legged, mobile, yellow-colored young, called “crawlers.” This stage spreads the infestation to new areas on the host plant, including bark, leaves and fruit, and to new hosts. After inserting their thread-like mouthparts into the plant and feeding for 2 to 3 days, female crawlers secrete their initial scale coverings and never move from that spot. Males develop into 2-winged adults in 2 or 3 weeks and emerge from their scales to seek females to mate. Up to six generations may be produced annually. All stages of development can occur throughout the year except during the winter.
Crape Myrtle Bark Scale
The crape myrtle bark scale, Acanthococcus (Eriococcus) lagerstromiae (Kuwana) was first confirmed in the USA in 2004 in the landscape near Dallas (TX), although it was likely introduced earlier. The scale is a sucking insect that feeds on the phloem (sap) of plants. As it feeds, it excretes a sugary solution known as “honeydew” (similar to aphids, whiteflies, and other sucking insects). Heavy infestations of crape myrtle bark scale produce sufficient honeydew to coat leaves, stems and bark of the tree. This honeydew, in turn, will eventually turn black as it is colonized by a concoction of fungi, called sooty mold. Although crape myrtles rarely die as a result of crape myrtle bark scale infestation, the sticky leaves and black trunks greatly reduce the attractive appearance of the tree.
Photo by Erfan K. Vafaie, Texas A&M AgriLife Extension.
Immature crape myrtle bark scale is hard to see with the naked eye, but adult scale covers, and egg sacs are frequently visible on the upper branches and trunk of the tree. These scales include larger, white, oval (female) and smaller, elongate (male) scales. Both male and female scales of the crape myrtle bark scale are immobile and will “bleed” pink blood when crushed.
Mealybugs are prominent now in Greenhouses and Houseplants
Mealybugs are soft-bodied, wingless insects belonging to the family Pseudococcidae. These pests are known for their damaging effects on a wide range of plants, including crops, ornamentals, and houseplants. Their appearance is distinctive: adults are covered with a white, waxy, cotton-like secretion, making them resemble small tufts of cotton. This protective coating helps conserve moisture and offers some defense against predators and pesticides. Understanding the biology of mealybugs is crucial for developing effective management strategies in agricultural and horticultural systems.
Mealybugs have a complex life cycle that includes egg, nymph (crawler), and adult stages:
- Egg: Female mealybugs lay hundreds of eggs within an ovisac, a protective sac made from waxy secretions. The color and size of the ovisac can vary among species.
- Nymph (Crawler): After hatching, the nymphs, or crawlers, emerge to find feeding sites. This is the most mobile stage of the mealybug life cycle, and it’s when they are most vulnerable to control measures. Crawlers are tiny, yellowish, and lack the waxy coating seen in adults.
- Adult: As they mature, nymphs undergo several molts before reaching adulthood. Adult females are larger than males and retain the waxy coating. Males may develop wings, depending on the species, and do not feed on plant sap as adults.
Mealybugs feed by inserting their long, slender mouthparts into plant tissues and sucking out sap. This feeding behavior can weaken plants, reduce growth, and cause leaf yellowing, wilting, and even death in severe infestations. As they feed, mealybugs excrete honeydew, a sticky substance that can lead to the growth of sooty mold, further impairing photosynthesis and plant health.
Mealybug reproduction can be sexual or asexual, varying by species. Some species are capable of parthenogenesis, where females produce offspring without mating. This ability allows for rapid population increases under favorable conditions.
Mealybugs spread primarily through human activity, such as the movement of infested plant material, and natural means, like crawling to adjacent plants or being carried by wind, animals, or ants. Ants, in particular, are known to farm mealybugs for their honeydew, protecting them from natural enemies and inadvertently aiding in their dispersal.
Introduction of Natural Predators or Disease
Controlling scale or mealybug insects in an organic farming system emphasizes the integration of biological and ecological methods to maintain pest populations below damaging levels. Biological control, one of the cornerstone practices in organic agriculture, involves the use of living organisms—predators, parasitoids, and pathogens—to regulate pest populations. Here are some effective methods to manage these insects through biological or predator-based strategies:
- Lady Beetles (Coccinellidae): Many lady beetle species are voracious predators of scale insects in their larval and adult stages. For instance, the vedalia beetle (Rodolia cardinalis) has been successfully used to control cottony cushion scale in citrus groves.
- Cryptolaemus montrouzieri: Often referred to as the mealybug ladybird, this beetle is a voracious predator of mealybugs in both its larval and adult stages. It has been used successfully in various agricultural systems to control mealybug populations.
- Lacewings (Chrysopidae): Green and brown lacewings consume scale insects during their larval stages. Green lacewing larvae are effective predators of mealybugs, consuming them at various stages of their development. Their larvae are known as “aphid lions” for their predatory efficiency.
- Parasitic Wasps: Tiny wasps, such as Aphytis melinus and Encarsia spp., specialize in parasitizing scale insects. They lay their eggs in or on the scale insect, and the developing larvae consume the scale from the inside. Several species of parasitic wasps, such as Leptomastix dactylopii, target mealybugs specifically. These wasps lay their eggs in or on mealybug larvae, and the hatching wasps consume the mealybugs from the inside.
- Beauveria bassiana and Metarhizium anisopliae are fungi that infect and kill a wide range of insect pests, including scale and mealybug insects. These fungi are particularly useful in humid environments where they can naturally proliferate and infect scale populations.
- Isaria fumosorosea (formerly known as Paecilomyces fumosoroseus) is a naturally occurring entomopathogenic fungus that acts as a biological control agent against a wide range of insect pests, including mealybugs, aphids, whiteflies, thrips, and other soft-bodied insects. It infects its hosts through the cuticle, leading to the pest’s death, and is particularly useful in integrated pest management (IPM) systems in organic agriculture and greenhouse settings.
Below you will see a list of organic products that have scale and/or mealybugs on their labels. These include some of the beneficial fungi listed above as well as botanical oils and the still very popular Azadirachtin extracted from the neem tree. You can just look through this short list or click on the link below to either see it on your computer or download and use as an Excel file.
Texas A&M AgriLife Organic 