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You are here: NRS Home / Research Programs / Forest Disturbance Processes / Invasive Species / Hemlock Woolly Adelgid / Control and Management / Biological Control / Scymnus coniferarum: A Predator of Hemlock Adelgids in Western North America
Hemlock Woolly Adelgid

Scymnus camptodromus Rearing and Evaluation

Research Issue

[photo:] Newly hatched Scymnus camptodromus larva.Although three predatory beetles (Sasajiscymnus tsugae Laricobius nigrinus and Laricobius osakensis) have been established for biological control of hemlock woolly adelgid (HWA), these are spreading slowly.  Additionally, three lady beetles of the subgenus Scymnus (Neopullus) were imported from China as a potential biological control agent for HWA and have been approved for release from quarantine.  Scymnus camptodromus has a high likelihood of being established in the U.S. as a major natural enemy of adelgid for several reasons. It is a voracious predator on HWA and was the most abundant predator in Yunnan Province in 2006, it has a phenology that is closely matched with that of the adelgid, and it is highly abundant over a broad geographic range in China. An additional advantage is that it has an earlier larval feeding period than other Scymnus spp. being investigated and thus may have greater impacts on adelgid populations.  Work on S. camptodromus has been limited because of an egg diapause.  Given the potential of this species for control of the adelgid, and its ability to thrive in colder climates, studies on this species should be accelerated.

Our Research

  • Determine the conditions needed to break the egg diapause
  • Complete non-target testing of S. camptodromus adults and larvae in the presence and absence of the host plant
  • Assess larval developmental rate and predation
  • Develop mass-rearing procedures for S. camptodromus
  • Conduct bagged release studies of S. camptodromus on adelgid-infested hemlock

Expected Outcomes

Non-target testing results will be used in an environmental assessment for permission to free release S. camptodromus to control the adelgid.  Field rearing methods can be used to increase the numbers of beetles available.  Field testing will provide a measure of the potential effectiveness of this predator.  An environmental assessment will be developed using the data obtained to make free field releases of this beetle possible.

Research Results

Scymnus camptodromus, imported from China, is being reared and evaluated in the Forest Service quarantine laboratory, Ansonia, CT.  This species has a broad geographic range and is consistently present over a wide range of habitats and adelgid densities.  Previously, work on S. camptodromus had been limited because of an egg diapause but now methods to break the diapause and rear the beetles have been worked out.  Eggs chilled at 5 °C for 2 or 3 months results in > 80 percent hatch of the eggs when they are moved to 10 °C (average of 60 and 40 days to hatch, respectively).   Eggs do not hatch as well if held for shorter times at 5°C or if moved to higher temperatures after the chill period

In no-choice adult feeding trials the adults fed on eggs of Adelges cooleyi, A. laricis, and Pineus strobi when they were removed from the egg mass and no host material was present, but they fed very little on them if presented on the host in the egg mass with the female adelgids.  The adults will also feed on the more exposed spring generation of A. laricis adults and nymphs on its host material.  Adults will also feed on first instar Aphis gossypii when presented without a host.  In a choice test adults feed almost exclusively on adelgid eggs or adults and only a couple of adults fed on a few P. strobi eggs. 

Development time and prey consumption of Scymnus camptodromus larvae by instar, strain, and temperature were evaluated. We observed that temperature had significant effects on the predator’s life history. The larvae tended to develop faster and consume more eggs of A. tsugae per day as rearing temperature increased; 23 egg/day at 15°C and 31 eggs/day at 20°C. However, as larvae took longer to develop at the lower temperature, the total number of eggs consumed per instar during larval development did not differ significantly between the two temperatures. A single larva consumed 450-550 HWA eggs to complete development. The lower temperature at which the predator larval could develop was estimated to be 5°C, which closely matches that of HWA progrediens. Accumulated degree-days for 50% of the predator neonates to reach adulthood was estimated to be 424. Although temperature had a significant effect on larval development and predation, it did not impact survival, size, or sex ratio of the predator at 15 and 20°C. Furthermore, no differences were observed among different geographical populations of the predator.

Confined field studies of S. camptodromus adults over the field seasons of 2012 and 2013 showed a significant reduction in HWA populations. In 2012 HWA there were 12% fewer eggs remaining when S. camptodromus adults were present compared to the unbagged branches.  Similarly, there were 27% fewer HWA eggs in bags with the predator compared to those without when the bags were checked biweekly during the 2013field season.  Also in 2013, there was a 35% reduction in the number of HWA settled crawlers when the predator was present compared to the unbagged branches. Under the conditions of our studies, S. camptodromus showed evidence of being an effective predator of HWA with close synchrony to the HWA life cycle.  A request for unconfined release was made to NAPPO and initially declined with a request for more information.  While obtaining the additional information needed the colony was lost and obtaining more from China would be extremely difficult at this time.

Limbu S, Cassidy K, Keena MA, Tobin P, and Hoover K. 2016.  Host range specificity of Scymnus camptodromus (Coleoptera: Coccinellidae), a predator of hemlock woolly adelgid. Environ. Entomol.45(1):94-100

Limbu, Samita; Keena, Melody A.; Long, David; Ostiguy, Nancy; Hoover, Kelli. 2015. Scymnus camptodromus (Coleoptera: Coccinellidae) larval development and predation of hemlock woolly adelgid (Hemiptera: Adelgidae). Environmental Entomology. 44(1): 81-89.

Limbu S, Keena MA, and Hoover K.. 2015. Petition for Unconfined Field Release of the Exotic Predator Scymnus camptodromus for Biological Control of Hemlock Woolly Adelgid (Adelges tsugae), in the Eastern United States.  Submitted to NAPPO

Keena, Melody A.; Trotter III, R. Talbot; Cheah, Carole; Montgomery, Michael E. 2012.Effects of temperature and photoperiod on the aestivo-hibernal egg diapause of Scymnus camptodromus (Coleoptera: Coccinellidae). Environmental Entomology. 41(6): 1662-1671.

Montgomery, ME; Keena, MA. 2011. Chapter 5: Scymnus (Neopullus) Lady Beetles from China. Pp. 53-76  In: Reardon, R. and Onken, B., eds.  Implementation and status of biological control of the hemlock woolly adelgid.  USDA For. Serv. FHTET 2011-04.

Keena, Melody. 2006. Work on third Scymnus beetle progressing, In: Onken, Brad; Souto, Dennis, eds., Hemlock Woolly Adelgid Newsletter, Issue No. 7, U.S. Department of Agriculture, Forest Service, Northeastern Area State and Private Forestry, Forest Health Protection:12.

Research Participants

Principal Investigators

  • Katie Cassidy, Master’s Candidate, Penn State University, Department of Entomology
  • Kelli Hoover, Associate Professor, Penn State University, Department of Entomology
  • Samita Limbu, Doctoral Candidate, Penn State University, Department of Entomology
  • Melody Keena, Research Entomologist, U.S. Forest Service, Northern Research Station

Research Partners

  • Michael Montgomery, U.S. Forest Service, Northern Research Station, Research Entomologist (Retired)


Last Modified: 07/12/2017

About this Research Area

Science theme: Forest Disturbance Processes

Science Topic: Invasive Species

About Hemlock Woolly Adelgid
Biological Control
Featured Publication

Keena, Melody. 2006. Work on third Scymnus beetle progressing, In: Onken, Brad; Souto, Dennis, eds., Hemlock Woolly Adelgid Newsletter, Issue No. 7, U.S. Department of Agriculture, Forest Service, Northeastern Area State and Private Forestry, Forest Health Protection:12.