Report on the Adelgids and Ladybugs in Hemlock Gorge

Final Report

Pseudoscymnus tsugae Release

Hemlock Gorge 2001-2005


The Department of Conservation and Recreation (DCR) (formerly the Department of Environmental Management) was approached by the Friends of Hemlock Gorge regarding the possible release of the predatory ladybird beetle (Pseudoscymnus tsugae) for the control of an infestation of Hemlock Woolly Adelgid (HWA) (Adelges tsugae) at the Hemlock Gorge in Newton.  A site visit was conducted with the USDA Forest Service to determine if the site met the federal release criteria. It was determined that the site did not meet these criteria because of extremely high HWA populations. Through the efforts of The Friends of Hemlock Gorge a $60,000 earmark was included in the Metropolitan District Commission’s (MDC) state budget to purchase the predatory beetles. This money was transferred to the Department of Conservation and Recreation’s budget because the MDC lacked the necessary resources to release and monitor the beetle release. Three releases were conducted in 2001 and 2002 as indicated in the chart below. 

Release DateQuantitySource
May 2, 20015000 AdultNJ Dept of Agriculture
June 6, 20015000 Adult and LarvaeEcoscientific Solutions
May 16, 20025011 AdultEcoscientific Solutions

Procedure and Data

The DCR determined that the most efficient way to monitor these release was to follow the federal guidelines even though no federal money was involved in the release.

The results of three years of monitoring are presented below.

DateHWA DensityHemlock HealthNo. AdultsNo. Larvae
June 6, 2001HighFair150
July 25, 2001HighFair231
August 16, 2001HighFair30 Plus0
Sept. 18, 2001HighFair10
May 17, 2002HighFair32
June 27, 2002HighFair121
July 25, 2002HighFair70
August 23, 2002HighFair40
June 27, 2003LightFair00
July 31, 2003LightFair00
August 14, 2003LightFair00
June 17, 2004LightGood00
Sept.21, 2004LightGood00
Sept 28, 2005LightGood00


The predatory ladybird beetle Pseudoscymnus tsugae in considered to be established at the Hemlock Gorge in Newton. This conclusion was reached because the beetles were recovered in the year following a release and immature beetles were also collected, which indicates the presence of a breeding population. Several adults were collected 75 feet from the original release site. I firmly believe the beetles are still present at the Hemlock Gorge, but because of the reduction of the HWA population the beetles were forced to disperse greatly in search of food. The other factor that has hindered our ability to locate them is the fact that there are a limited number of live hemlock branches reachable from the ground to sample.

The health of the hemlocks appears to be improving as indicated by an improvement in the color of the foliage and the presence of new growth. A combination of several factors is responsible for this improvement:

  • Extremely low temperatures during the winter of 2002-03 resulted in as much as 90% mortality of the adelgid population.
  • The large amount of moisture we received during the 2003 growing season.
  • The presence of the ladybird beetles.

During this past fall I spent considerable time at the Gorge attempting to recover beetles.  These efforts were not productive.  I am however convinced that the beetles are still present.  I also noted that many of the trees were producing new growth and that on some of this new growth immature HWA was observed. 

I will continue to make yearly visits to the Gorge of observe the condition of the hemlocks and hopefully recover the predatory ladybird beetles.

Charlie Burnham