Biological Control of Pests in Forests of Eastern United States

 

 

Euonymus Scale (Unaspis euonymi)

Roy Van Driesche and Amber O'Reilly

University of Massachusetts, Amherst

vandries@nre.umass.edu

Range in North America

Euonymus scale, Unaspis euonymi (Comstock), is a diaspidid scale of Asian origin (China or Japan) that is found throughout the temperate parts of the United States as a pest of landscape plants in the genus Euonymus. It is not generally a pest of natural areas, even though there are some native plants in this genus.

Damage

Landscape plants in the genus Euonymus, especially Euonymus fortunei (L.) are damaged by high densities of this scale, which shorten the life in the landscape of heavily infested plants . In Massachusetts, plants with heavy scale populations died at an annual rate of 12%, versus only 3% for non-infested or lightly infested plants (Van Driesche et al., 1998a).  Heavily infested plants are unsightly, and have reduced growth and vigor.

Resident Natural Enemies

Only one natural enemy, Encarsia (formely Aspidiotiphagus) citrina (Crawford), was commonly associated with euonymus scale in the eastern United States before biological control introductions were begun. This parasitoid was detected at 44% of 79 locations sampled in southern New England by Van Driesche et al. (1998b) and caused 13-34% parasitism of adult female scales, depending on the generation. Parasitism levels, however, did not show any correlation to scale density and did not preclude the scale from reaching damaging levels.  The identity of this parasitoid is now uncertain, as recent evidence shows that E. citrina is not a single species, but a group of cryptic species grouped erroneously under the same name (Abell, unpublished).  The native coccinellid, Chilocorus stigma (Say), is occasionally found feeding on euonymus scale as well, but is not common and has no impact on scale density.

Biological Control Efforts Against the Pest

A classical biological control program against euonymus scale was initiated by the United States Department of Agriculture (USDA-ARS) in the early 1980s, with the introduction from Korea of the coccinellid Chilocorus kuwanae (Silvestri) and the nitidulid Cybocephalus nr. nipponicus Enrody-Younga (Drea and Carlson, 1987, 1988). Further work was done by USDA-APHIS in the 1990s in cooperation with various university-based biological control scientists, including the University of Massachusetts.  During this period, predators and parasitoids were collected from euonymus scale in China in the area near Beijing, which was selected as a climatic match to southern New England.  This work resulted in the same two predators being reimported (as strains better adapted to colder areas), as well as the three aphelinid parasitoids Coccobius sp. nr. fulvus (Compere et Annecke), Encarsia sp. nr. diaspidicola (Silvestri) and Aphytis sp. (Van Driesche et al., 1998b). Under APHIS auspices, in cooperation with mass rearing facilities in various states, especially in New Jersey, releases of these natural enemies were made throughout the United States. In Southern New England, both predators established and C. kuwanae became widespread and sufficiently abundant that it reduced the proportion of landscape euonymus plants with high density scale infestations (in Massachusetts) from 19.2 to 11.6% (Van Driesche et al., 1998c; Van Driesche and Nunn, 2003). Cybocephalus nr. nipponicus established in Massachusetts, but its current status is not clear and needs to be resurveyed. The biology of this species (Alvarez and Van Driesche, 1998a,b) suggests this predator may be important in regulating low density populations of the scale, since few scales are needed for complete development per beetle larva.  In New Jersey, this predator has become wide spread (Matadha et al., 2003).  In Massachusetts, two of the three parasitoids (C. nr fulvus and E. nr. diaspidicoloa) were recovered at release sites in several years immediately following their release (Van Driesche et al., 1998b). 

Up to the Minute Status

In 2006 and 2007, surveys in western Massachusetts (O'Reilly and Van Driesche, unpub.) detected widespread establishment of C. nr. fulvus, one of the three parasitoids released ca 15 years ealier.

Photos

Upper left: close up of euonymus scale showing adult females (brown) and second stage males (white) (photo credit: US National Collection of Scale Insects Photographs, Forestryimages.org)

upper right: infested euonymus foliage (photo credit: John A. Weidhass, Forestryimages.org).

References Cited

Alvarez, J.M. and R.G. Van Driesche. 1998a. Biology of Cybocephalus sp. nr. nipponicus (Coleoptera: Cybocephalidae), a natural enemy of euonymus scale (Homoptera: Diaspididae). Environmental Entomology 27: 130-136..

Alvarez, J.M. and R. G. Van Driesche. 1998b. Effect of prey sex, density, and age on oviposition of Cybocephalus sp. nr. nipponicus (Coleoptera: Cybocephalidae), a natural enemy of euonymus scale (Homoptera: Diaspididae). Florida Entomologist 81: 429-436.

Drea, J. J. and R. W. Carlson. 1987. The establishment of Chilocorus kuwanae (Coleoptera: Coccinellidae) in eastern United States. Proceedings of the Entomological Society of Washington 89: 821-824.

Drea, J. J. and R. W. Carlson. 1988. The establishment of Cybocephalus sp. (Coleoptera: Nitidulidae) from Korea on Unaspis euonymi (Homoptera: Diapididae) in eastern United States. Proceedings of the Entomological Society of Washington 90: 307-309.

Matadha, D., G. C. Hamilton, M. G. Hughes, and J. H. Lashomb. 2003. Distribution of natural enemies of euonymus scale, Unaspis euonymi (Comstock) (Homoptera: Diaspididae), in New Jersey. Environmental Entomology 32: 602-607.

Van Driesche, R. G., P. Kingsley, M. Rose, and M. Bryan. 1998a. Effect of euonymus scale (Homoptera: Diaspididae) on Euonymus spp. survival in New England, with estimates of economic costs of pest damage. Environmental Entomology 27: 217-220.

Van Driesche, R.G., K. Idoine, M. Rose, and M. Bryan. 1998b. Release, establishment and spread of Asian natural enemies of euonymus scale (Homoptera: Diaspididae) in New England. Florida Entomologist 81: 1-9.

Van Driesche, R. G., K. Idoine, M. Rose, and M. Bryan. 1998c. Evaluation of the effectiveness of Chilocorus kuwanae (Coleoptera: Coccinellidae) in suppressing euonymus scale (Homoptera: Diaspididae). Biological Control 12: 56-65.

Van Driesche, R. G. and C. Nunn. 2003. Status of euonymus scale in Massachusetts fourteen years after release of Chilocorus kuwanae (Coleoptera: Coccinellidae). Florida Entomologist 86: 384-385.