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Hemlock Woolly Adelgid

Release and Evaluation of Scymnus ningshanensis

Research Issue

[photo:] Scymnus ningshanensis, a lady beetle from ChinaScymnus ningshanensis Yu et Yao is the third in a series of lady beetles (Coccinellidae) in the subgenus Neopullus imported from China as a potential biological control for the hemlock woolly adelgid, Adelges tsugae Annand (HWA). Its biology and host specificity was first studied in the U.S. Forest Service Quarantine Laboratory in Ansonia, CT. After it was documented to have good potential as a predator specifically of adelgids (Montgomery 2002, Butin et al. 2004), it was approved for release from quarantine. Research was then initiated on methods to mass rear it and establish it in forested environments.

Research Results

Rearing the large numbers of Scymnus ningshanensis needed for field releases was done only by the Forest Service research group in Hamden, CT. In the lab, the beetles normally start laying eggs in February at 10-15°C when provided foliage with the adelgid in the egg stage. The beetles will continue to lay eggs until July, if they continue to receive HWA eggs as food. A bottleneck in mass rearing is that the new beetles must be held until the next year and many die in the late summer, when they have only diapausing adelgid nymphs for food.

The impact of S. ningshanensis on the population biology of HWA was evaluated in sleeve cages. Branch tips infested with 100-400 adelgid ovisacs were selected in early April, when the overwintering generation of HWA had just started to lay eggs. The adelgid woolly masses on a hemlock branch were counted, and the treatments (cages with or without beetles) were randomly assigned. Mesh bags were used to cover both the control branches without beetles and treatment branches with either a single female beetle or a male/female pair.  In late June, when the spring generation of the adelgid was mature, the bagged branches were brought to the laboratory where the adelgids and lady beetles were counted and compared to thex original counts.

As expected, HWA populations declined more in the bags containing Scymnus beetles than in the control bags.  However, the extent of the lady beetle’s impact appears to be affected by the condition of the adelgid population before being bagged.  If the control adelgid population was low and rapidly increasing, the beetles dramatically reduced the HWA increase; if the control population was declining because of a reduction in host nutritional value, the lady beetle impact on HWA was relatively small. Preconditioning the beetles for several weeks at simulated winter conditions before placement in the field also influences their effectiveness.

Limited releases of a few hundred adult S. ningshanensis were made in Connecticut, Massachusetts and North Carolina in 2007-2009, but there is no evidence of establishment.

Montgomery, M. E.; Keena, M. 2011. Scymnus (Neopullus) lady beetles from China. In: Onken, B.; Reardon, R. eds. Implementation and status of biological control of the hemlock woolly adelgid. FHTET-2011-04. Morgantown, WV: U.S. Department of Agriculture, Forest Service Forest Health Technology Enterprise Team: 53-76. Chapter 5.

Butin, E.; E.; Havill, N. P.; Elkinton, J. S.; Montgomery, M. E. 2004. Feeding preference of three lady beetle predators of the hemlock woolly adelgid (Homoptera: Adelgidae). Journal of Economic Entomology. 97: 1635-1641.

Butin, E.; Elkinton, J.; Havill, N.; Montgomery, M. . 2003. Comparison of numerical response and predation effects of two coccinellid species on hemlock woolly adelgid (Homoptera: Adelgidae). Journal of Economic Entomology. 96: 763.

Montgomery, M. E.; Wang, H.; Yao, D.; Lu, W.; Havill, N.; Li, G. 2002. Biology of Scymnus ningshanensis (Coleoptera: Coccinellidae): a predator of Adelges tsugae (Homoptera: Adelgidae), In: Onken, B.; Reardon, R.; Lashomb, J., eds., East Brunswick, NJ. Proceedings: hemlock woolly adelgid in the eastern United States symposium. Rutgers University:181-188.

Yu, G.; Montgomery, M. E.; Yao, D. 2000. Lady beetles (Coleoptera: Coccinellidae) from Chinese hemlocks infested with the hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae). Coleopterists Bulletin. 54: 154-199.

Research Participants

Principal Investigator

  • Michael Montgomery, Research Entomologist, U.S. Forest Service, Northern Research Station
  • Melody Keena, Research Entomologist, U.S. Forest Service, Northern Research Station
  • Elizabeth Butin and Joseph Elkinton, University of Massachusetts, Amherst

Last Modified: 05/08/2015

About this Research Area

Science theme: Forest Disturbance Processes

Science Topic: Invasive Species

About Hemlock Woolly Adelgid
Biological Control
Featured Publication

Butin, E.; Elkinton, J.; Havill, N.; Montgomery, M. 2003. Comparative impact of Scymnus ningshanensis and Pseudoscymnus tsugae (Coleoptera: Coccinellidae) on the hemlock woolly adelgid. In: Fosbroke, Sandra L.C.; Gottschalk, Kurt W., eds. Proceedings, U.S. Department of Agriculture interagency research forum on gypsy moth and other invasive species 2002. Gen. Tech. Rep. NE-300. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station.