Anyone in the native range of the Eastern Hemlock may find interest in this. Or maybe not.
This is a great reference and I’ll refer to it exclusively for this discussion: https://www.fs.fed.us/foresthealth/technology/pdfs/HWA-FHTET-2014-05.pdf
Please take some time to read the whole document, as it is a really nice source of information on the Hemlock Wooly Adelgid (HWA).
Some states are waging biological warfare on the the Hemlock Wooly Adelgid (Adelges tsugae Annand). Pennsylvania is one of them. From an ecosystem and environmental standpoint, this bio-battle is tricky business.
“The primary objective of biological control is to introduce a group of natural enemies considered important in the native habitat and deemed safe for introduction into the eastern United States,” (Page 13).
Mainly because there are no specialized predators of the adelgid, insects and fungal pathogens are introduced to prey on HWA. The suitability of a pathogen or predator comes from studying natural enemies of the HWA in places like Western North America and Asia where these natural controls already exist in strong populations. The long term effects are yet to be documented, as the the process of synthesis and analysis on this topic is in its infancy.
Fungal Pathogens
“Twenty fungal genera and 79 entomopathogenic fungus isolates were found in association with HWA in the eastern United States and southern China. Of all the isolates, no putative specialists were found. A combination of generalist fungi that included two strains of Beauveria bassiana Balasamo, one of Lecanicillium lecanii Zimmermann, and one of Metarhizium anisopliae Metchnikoff, demonstrated high efficacy against HWA. A commercially available Lecanicillium lecanii formulated with a whey carrier has been tested in small-scale forest trials and has been shown to be effective, especially against early instar HWA before they produce wool. This augmentative approach is still in the early developmental stages” (Page 13).
Predators
There are several types of predatory beetles currently being monitored and researched as effective predators against HWA.
“Predator collection started in Japan in 1992 and field releases occurred in North America in 1995 and included Sasajiscymnus tsugae (Sasaji and McClure) (Coleoptera: Cocinellidae)” (Page 13). This introduction is currently being phased out but monitoring still continues.
We see here a small hint of the complexity of biological controls. Just because something works in it’s native setting doesn’t necessarily mean it proves to be beneficial in a similar environment.
“Three previously unknown lady beetles (Coleoptera: Coccinellidae), Scymnus camptodromus Yu et Liu, Scymnus sinuanodulus Yu et Yao, and Scymnus ningshanensis Yu et Yao, were found to be the most abundant predators in different locations. The predators were imported, evaluated in quarantine, and cleared for release. However, due to difficulties in mass rearing, releases of S. ningshanensis and S. sinuanodulus were delayed until 2004, and S. camptodromus was not released. There were no recoveries of the first two species following their limited releases, and work continues on rearing of S. camptodromus,” (Page 14).
“Laricobius beetles in the family Derodontidae are specialist predators of adelgids. In 1997, a predator native to western North America, Laricobius nigrinus Fender, was found to consistently feed only on HWA in the lab, and its life cycle was shown to be synchronous with HWA. Oviposition and subsequent larval development coincides with oviposition by the HWA sistens adults. Females oviposit within HWA ovisacs from January to March. After hatching, larvae go through four instars and mature larvae drop to the soil to pupate within two weeks. Eclosed adults remain in the soil in a state of aestival diapause that coincides with diapausing the first instar sistentes. Adults resume activity in the fall coinciding with resumption of development by HWA.
Following host-range testing studies in quarantine, the predator was cleared for release in 2000. Rearing procedures were developed and releases began in 2003. To date, more than 200,000 beetles have been released at over 200 sites. Evaluations after release showed that establishment is positively correlated with minimum winter temperature and with the number of beetles released. Beetles initially disperse slowly up the release tree and then away from the release tree at a rate of close to 40 m/yr. Some anecdotal evidence suggests this could be greater at times,” (Page 14).
In this example, we see that if the lifecycle of both the pest and the predator of that pest coincide, the biological control may be more effective in its role of controlling the pest. How amazing to consider this ebb and flow of the natural world, and how timing sometimes really is everything, especially when devising an IPM plan.
“Because the strain of HWA that was introduced to eastern North America is from southern Japan, an additional effort was made to look for natural enemies in this location. A new species, Laricobius osakensis Montgomery and Shiyake, was discovered in 2005 and imported to quarantine to study its biology and host-range (Figure 17). The insect was also studied in its native habitat. Laricobius osakensis has host preferences similar to L. nigrinus, greater fecundity, and a higher predation rate then L. nigrinus. Lab studies showed that it cannot hybridize with the North American Laricobius species,” (Page 15).
In this sense, fecundity is actually a favorable trait in an effective predator.
“In its native habitat, it is shown to be the key natural enemy on sistentes, being consistently present in association with HWA, and having a synchronous life cycle with HWA. Its population uctuations were correlated with those of the HWA sistens population, and it was shown to reduce populations of HWA on T. seiboldii. Permission to remove L. osakensis from quarantine was received in 2010 and the rst open releases began in 2012. Continued efforts toward large-scale operational releases and monitoring of this predator are underway,” (Page 15).
Whatever your stand is on biological control, on the surface it truly is fascinating. I guess time will tell how disruptive or beneficial it can be in the ecosystem.
How many different types of factors play a role in the effectiveness of biological controls on the HWA is really amazing. Consider the ecosystem as a whole. We know that these predators operate in similar climates and landscapes, and on similar plants and insects, but introducing biological controls is not an easy task. From overwintering, to monitoring and rearing the insects prior to introduction; all stages of this biological warfare has many challenges. On top of that, in North America our research only goes back to 1992, so this topic is on the frontline of current research, and has the room to grow and improve exponentially.
For me, in the most basic sense, Biological Control gives a whole new meaning to the term sub-contractor, that’s for sure.
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