Hawthorn mealybug, Phenacoccus dearnessi
Order: Hemiptera
Family: Pseudococcidae
Description
The hawthorn mealybug is an introduced species in Colorado. It feeds on twigs and small branches of hawthorn (Crataegus spp.), mountain ash (Sorbus spp.), juneberry (Amelanchier spp.), and other plants in the family Rosaceae. This pest produces copious amounts of honeydew and has piercing-sucking mouthparts for piercing plant tissues and extracting plant fluids. Adult females measure about 3.2 mm (1/8 inch) and have globular, red bodies covered with secretions of white wax, while adult males are smaller, have wings, and are typically present during the spring as individuals migrate from overwintering sites to twigs. The red or brown nymphs (crawlers) are generally smaller and more elongated than adult females.
Quick Facts
- Hawthorn mealybug is an introduced species in Colorado that can attack certain plants in the family Rosaceae. Cultivars of hawthorn, including English hawthorn, Arnold hawthorn, and Thornless cockspur hawthorn, are more susceptible to infestations of this pest.
- While heavy infestations can defoliate and weaken plants, this pest does not usually cause significant injury. However, hawthorn mealybug produces copious amounts of honeydew which can facilitate the growth of sooty mold.
- The insect’s waxy covering and tendency to occupy crevices in bark make chemical control challenging. Timing the application correctly to target vulnerable nymphs is necessary for effective chemical control.
Adults and crawlers of hawthorn mealybug. Notice the red bodies of adults covered in wax, while the nymphs are smaller and have a tan or light brown color. Image credits: Whitney Cranshaw, Colorado State University, Bugwood.org
Nymph of hawthorn mealybug on a hawthorn leaf. Note the elongated, oval-shaped body. Image credits: Whitney Cranshaw, Colorado State University, Bugwood.org
Nymphs of hawthorn mealybug overwintering in bark crevices. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
The hawthorn mealybug overwinters as a late-stage nymph within bark crevices on the trunk and larger branches. Females migrate to twigs in the spring and continue developing until reaching maturity in late May or early June. Males remain near their overwintering sites on the trunk until they molt into their final winged form and begin mating. After mating, the adult female swells with hundreds of eggs. The newly emerged nymphs briefly feed on leaves before moving to protected areas on twigs where they remain for much of the summer. The peak abundance of nymphs typically occurs in late May and June, although wet, cool weather tends to delay dispersal of nymphs. After feeding and developing on twigs and within leaf folds through the summer, late-stage nymphs migrate to overwintering sites on trunks and larger branches during September and October.
Populations of hawthorn mealybug tend to be high late in the summer, and trees in landscapes tend to be more susceptible to attack than native stands. It is believed that one generation is produced each growing season in Colorado. However, egg producing females and egg hatch have been observed in late September, which suggests that this pest can either produce a second generation or has an extended egg-laying period.
Injury
Heavy infestations of hawthorn mealybug can lead to severe defoliation, twig dieback, and weakened plants. The production of honeydew can lead to the growth of black sooty mold, which can give the tree an unattractive appearance. The severity of feeding injuries inflicted by hawthorn mealybug differs among hawthorn cultivars, with English hawthorn, Arnold hawthorn, and Thornless cockspur hawthorn appearing to be most susceptible.
Biological control
Green lacewing larvae and certain lady beetles are predators of hawthorn mealybugs. The presence of predators can often limit the density of hawthorn mealybug to acceptable levels, eliminating the need for insecticides.
Chemical control
Chemical control of hawthorn mealybug is challenging due to the insect’s waxy covering and habit of occupying cracks and crevices in bark. Insect growth regulators are relatively safe for beneficial insects and can be applied when crawlers migrate from overwintering sites to twigs in the spring. Late summer or early fall applications can also provide some control against hawthorn mealybug. Dormant oils can be effective when applied to trunks and undersides of branches where hawthorn mealybug overwinters.
While systemic insecticides can control hawthorn mealybug, the toxin can accumulate in nectar and poses a risk to pollinators. Furthermore, hawthorn flowers are attractive to foraging honeybees in Colorado, which further puts these beneficial insects at risk. Given this, systemic insecticides should only be applied after bloom.
References
CSU. (n.d.). Hawthorn Mealybug. Colorado State University – Colorado Insect of Interest. Available https://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/Hawthorn%20Mealybug%20December%202014%20Revision.pdf
CSU. (n.d.). Hawthorn Mealybug. Colorado State University – Plant Talk Colorado. Available https://planttalk.colostate.edu/topics/insects-diseases/1457-hawthorn-mealybug/
UMN. (n.d.). Hawthorn mealybug. University of Minnesota – Extension. Available https://apps.extension.umn.edu/garden/diagnose/insect/trees-shrubs/not-obvious/hawthornmealybug.html
UNL. 2021. A Bug’s Life: Hawthorn mealybug. University of Nebraska-Lincoln. Available https://extension.unl.edu/statewide/douglas-sarpy/pdfs/ce/resources/ce-abl-hawthorn-mealybug.pdf