Verbenone, or Splat Verb, is Not Effective as a Stand-Alone Agent Against the Western Pine Beetle

April 2016

Many homeowners associations and businesses are recommending the use of SPLAT Verb to protect ponderosa pine trees from being attacked by pine bark beetles. For example, this local article states “Verbenone is naturally produced by MPB and by several other species of bark beetle towards the end of a mass attack.”  This text exactly matches the text at the isatech.com website, so it appears not much work was put into researching this.

What the article, or any other local sources, bother to state, and probably do not know, is that SPLAT Verb, alone, is not effective against western pine beetles. The local promoters of the use of SPLAT Verb are confused, and are giving misleading information to the public.

The active ingredient, verbenone, is an anti-aggregation pheromone that works against the MOUNTAIN Pine Beetle (Dendroctonus ponderosae), not the WESTERN Pine Beetle (Dendroctonus brevicomis). These are different species, with different habits and ranges.

The pine bark beetle that is killing our Tuolumne and Calaveras County ponderosa pines is the western pine beetle, D. brevicomis.

The mountain pine beetle prefers sugar pine, lodgepole, knobcone, and smaller diameter ponderosa pines.  Mountain pine beetles are rarely found in ponderosa pines that are greater than 6 inches in diameter.  In California, western pine beetles are by far the most important beetle attacking ponderosa pines, of all sizes, and are the cause of most ponderosa pine mortality.

Verbenone is a naturally occurring substance, and is created by the oxidation of alpha-pinene, a component of pine resin. Mountain pine beetles and Southern Pine Beetles use verbenone as a pheromone, and react to it.

The work goes back to the early least the 1970s. Field Response of the Southern Pine Beetle to Behavioral Chemicals. And even this work showed that verbenone alone was questionable, stating: “Traps with a 1:4 mixture of Endo-brevicomin and verbenone plus an attractant caught significantly fewer beetles than traps with the attractant plus either one of the inhibitors.”

This 1980 paper states “Attempts to use verbenone to protect living trees from D. brevicomis attack were inconclusive.”  Effects of verbenone and trans-verbenol on the response of Dendroctonus brevicomis to natural and synthetic attractant in the field

This 2006 article also says that verbenone is not effective, as a stand-alone agent, against western pine beetles: Efficacy of Verbenone for Protecting Ponderosa Pine Stands From Western Pine Beetle (Coleoptera: Curculionidae: Scolytinae) Attack in California. It states: “No significant differences in levels of D. brevicomis-caused tree mortality or the percentage of unsuccessfully attacked trees were found between verbenone-treated and untreated plots during each year or cumulatively over the 3-yr period.” That means that trees treated with verbenone did no better than untreated trees.

There is also concern within the USDA Forest Service about the use of verbenone. Ken Gibson, of the USDA Forest Service, states, in a position paper on the use of verbenone, that results are inconsistent. There is even concern that low levels of verbenone will attract mountain pine beetles. See Using Verbenone to Protect Host Trees from Mountain Pine Beetle Attack. To quote from the paper: ” This lack of consistency in some verbenone trials has been a source of great frustration to the bark beetle research community.” He goes on to say “if someone were to ask any of us if verbenone protects host trees from MPB (mountain pine beetle) attack, we would have to honestly reply, “Sometimes!”  A “silver bullet” verbenone is not!”

The conclusion is this: Verbenone is not effective as a stand-alone treatment against the Western Pine Beetle. It has been shown to be ineffective against this species of beetle, over a three year period, and its effectiveness against even the mountain pine beetle is inconsistent.

Verbenone, in combination blends, shows some promise, for the Western Pine Beetle, but this research is ongoing, and no product is yet available. And yet again, inconsistent results are reported. Some samples of the papers are:

1. Efficacy of “Verbenone Plus” for Protecting Ponderosa Pine Trees and Stands From Dendroctonus brevicomis (Coleoptera: Curculionidae) Attack in British Columbia and California. 2012. The paper states that verbenone alone had no effect on the density or success of attacks against the pines. But the researchers created a blend of four semiochemicals (natural chemicals released by an organism that affect the behaviors of other individuals): acetophenone, (E)-2-hexen-1-ol + (Z)-2-hexen-1-ol, and (–)-verbenone. They termed this blend “Verbenone Plus”, and it showed potential. The paper states “Verbenone Plus significantly reduced the percentage of trees mass attacked by D. brevicomis in one study, but in a second study no significant treatment effect was observed.”

2. Verbenone Plus Reduces Levels of Tree Mortality Attributed to Mountain Pine Beetle Infestations in Whitebark Pine, a Tree Species of Concern  2012.

 

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