by Mattie Vandiver

The hemlock woolly adelgid (HWA) is an insect native to Japan that was first noted in Connecticut in 1985 when a foliage sample was brought to the research station in New Haven. Since then it has been an ongoing issue in Connecticut as well as many other states, although Norfolk has barely been affected until recently because of its cold winter temperatures. HWA dies in temperatures below zero, so fluctuations of the adelgid population are often linked to the severity of  winters. The last two winters in Norfolk have been mild with warmer temperatures, which has caused an increase in the HWA population. Dr. Carole Cheah, a research entomologist at the Connecticut Agricultural Experiment, found an increase of HWA in five locations in Great Mountain Forest just last month. 

What makes HWA even more of a threat to hemlocks is that they are already facing other dangers. Many hemlocks in Connecticut are currently under drought stress. There is also a native insect called the hemlock borer, similar to the emerald ash borer, that lays its eggs in the hemlock and the larvae then ravage through the tree’s bark. “That’s what I fear the most,” said Cheah, “a combination of drought and hemlock borer following the hemlock woolly adelgid is what usually does the trees in.”

Cheah’s main tool for combating HWA is the biocontrol lady beetle Sasajiscymnus tsugae, a beetle that is also native to Japan and that preys on HWA. Because of the recent resurgence of the adelgid in many parts of the state, Cheah is encouraging more people to get involved with lady beetle control. Many people have reservations about using the lady beetle because it is a non-native insect, but Cheah says that she has never seen any negative consequences of the beetle in 26 years of releases in Connecticut and has never had any negative reports from other states where it is in use.

No non-native insect is allowed to be released without going through very strict federal environmental risk assessments, and the beetle fully passed the risk assessment for Connecticut in 1995. Connecticut was the first state to release this beetle and remained the only state doing so until 1999. The U.S. Forest Service became interested in releasing the beetle in other states in 1999, so they did a multistate federal risk assessment. The U.S. Fish and Wildlife subsequently did its own risk assessment and decided the lady beetle was a safe biocontrol agent.

“The reason I have confidence in this beetle,” said Cheah, “is that it is very specific. It is a major predator of the adelgid in Japan, and it is so in sync with the woolly adelgid that it really doesn’t eat anything else.” All stages of the lady beetle feed on all stages of HWA, which makes it a very effective predator. If the adelgid population does decrease and is confined to certain areas, the lady beetle will die because it doesn’t have enough of a food supply. The lady beetle also stays mostly with the hemlock trees, rarely wandering to another species of tree. This particular lady beetle is not the one normally seen around town; it is very small and hard to spot, about the size of a sesame seed. 

Until recently, there hasn’t been another biocontrol insect so readily available to the public. Even though the lady beetle can help in controlling HWA, it is not an immediate solution. Very small amounts of beetles are released in comparison to how many HWA there are. Over the years, research has shown that these beetles do decrease the population of HWA, and according to Cheah, the beetle gives us a chance to control HWA while we can.

Mid to late fall and winter is the best time to spot HWA. They are easiest to spot by turning over the tips of the branches to look underneath. If you spot HWA on trees on your property, there are a few methods of treatment that can be used. Pesticides, like insecticidal soap,  are an effective option, but they also pose environmental problems, especially to water sources by which hemlocks often grow.

Another option is to use a horticultural oil application, but not near water. Unlike pesticides, horticultural oils don’t persist in the environment; they just smother the insect, and the tree does not absorb them. Still, it’s good to be careful when applying the oil: apply in cool weather in either the morning or early evening. This treatment requires yearly reapplication, and it’s important to be thorough in applying because it is a contact type of control. This is the least damaging treatment that can be applied to specific hemlock trees and bushes around a house.