HWA Predator Beetles
Little Beetles with Big Appetites
Laricobius nigrinus, a predator beetle from the Pacific Northwest, feeds vigorously on Hemlock Woolly Adelgid throughout the winter months. L.nigrinus, otherwise known as “Little Lari” causes significant disturbance of HWA populations after establishment. (see controlled studies). Laricobius females predate on adelgids before depositing their eggs into HWA ovisacs in the late winter months. Larcobius larvae will develop through 4 instar stages before dropping to the forest floor to pupate and eventually emerge as adults in the fall (view studies on L.nigrinus synchrony & predation).
Hemlock Woolly Adelgid’s Natural Enemy
Laricobius nigrinus larvae (4th instar) complete their development through the winter on HWA ovisacs
Since Hemlock Woolly Adelgid arrived in the eastern United States over 30 years ago, entomologists searched desperately for a solution. Many biological control agents have been introduced in efforts to slow the spread of HWA, but none showed promising results of suppression or establishment…that is until we discovered Laricobius nigrinus.
With the help of a cryptic speciation study in the early 2,000s, entomologists discovered that HWA coexisted in Northwestern United States alongside its own unique set of predators. Among those predators, a little beetle named “Laricobius nigrinus” (AKA Little Lari) proved to be the keystone predator of HWA in the Pacific Northwest. Extensive studies were performed to test host specificity and phenology. The results were promising and the solution was simple: introduce L.nigrinus on the east coast and let nature do the rest (see top-down predation studies on efficacy). The question was, “Will L.nigrinus survive in a completely new environment?” Thanks to recent studies out of Virginia Tech, entomologists have confirmed L.nigrinus's establishment in our eastern forests! It is simply a matter of time before our predator beetle populations are stable and HWA is no longer a threat to the eastern hemlock.
Efforts by the U.S. Forest Service to mass rear and release L.nigrinus are already in place. To date, over 450,000 L.nigrinus beetles have been released on public lands to combat HWA (see predator release map). You, as a landowner, can accelerate the eradication of HWA and benefit from the release of this biological control.
Electron photo of 4th instar laricobius nigrinus larvae
Laricobius beetles are strong fliers, capable of traveling 2-4 km in a single season in search of their prey. Once L.nigrinus. adults emerge from the soil, they use a combination of visual and olfactory senses to locate HWA. Research suggests they may use specially adapt chemoreceptors to locate hemlock trees under attack by HWA. After locating a population of HWA, L.nigrinus predates on HWA throughout the winter until they are ready to begin the next generation of predator beetles. Females leave their eggs behind, nestled into the wool of HWA, where they develop into larvae which will consume the remaining adelgids leftover from the previous generation until they have reached maturity.
What Makes L.nigrinus the Perfect Predator?
Laricobius nigrinus is a specialist predator, preying only adelgids. It has evolved alongside Hemlock Woolly Adelgid in the Pacific Northwest and adapted to its lifecycle. L.nigrinus's phenology is perfectly synchronized with HWA’s development cycle. While Hemlock Woolly Adelgid has 2 generations per year (winter and summer), the winter generation (sisten) does the majority of damage to eastern hemlocks. Why? HWA, being an invasive species, has no native predators to keep its winter generation in check on the east coast. Thus, its population runs rampant during the winter months. L.nigrinus is critical to controlling populations of Hemlock Woolly Adelgid because it actively predates on HWA during the winter months (October-April). While most arthropods are hibernating in the soil, Laricobius nigrinus is busy munching away on Adelgids. L.nigrinus beetles pack themselves into the woolly ovisacs produced by HWA in order to withstand extreme cold conditions.
Original diagram, Cheah et al. (2004), modified by Lauren Michelle Gonzalez