This is a follow-up to the BYGL Alert I posted on June 17 titled, Be Alert to Magnolia Scale. You can access that Alert by clicking on this hotlink:
I posted the June Alert after I found a sizable magnolia scale (Neolecanium cornuparvum, family Coccidae (Soft Scale Insects)) infestation on a small saucer magnolia (Magnolia x soulangeana) in my home landscape. I was thrilled because I could closely monitor this native soft scale's development without needing to travel. This is the largest-sized soft scale found in Ohio. My wife was much less thrilled.
I was also thrilled to find lady beetle (family Coccinellidae) larvae lurking among the magnolia scale females. I identified the larvae as belonging to the genus Hyperaspis, collectively known as “Sigel lady beetles.” There are over 90 species of Sigel lady beetles making it the second-largest coccinellid genus north of Mexico.
However, I was much less thrilled when I discovered earlier this week that the Sigel lady beetle larvae had totally decimated my magnolia scale “private stock.” Magnolia scale is the largest-sized soft scale found in Ohio, but there is not a single magnolia scale female left for me to photograph when they reach their full glory. My wife is thrilled.
There is nothing more deceptive than an obvious fact. – Sir. Arthur Conan Doyle
Nature has been choreographing the dance between insect predators and their prey for millions of years. Predaceous insects along with parasitoids and pathogens (the “3-Ps”) are a major reason we commonly see plant pest populations rise and fall dramatically from year to year.
Still, relying on beneficial insects to massacre a plant pest requires a certain leap of faith – a faith in Nature – compared to the certainty that an insecticide will kill plant pests. It’s human nature to want to “do something” when something goes wrong, and spraying is doing something.
Of course, doing nothing is a good option compared to doing something wrong. Applying topical insecticides runs the risk of collateral damage by killing beneficial insects that can play an important role in suppressing populations of the targeted pest.
On the other hand, I would be overstating the case to imply predators are always as effective as I observed on my magnolia. This is why we include “chemical” and “cultural” along with “biological” as the three strategic pillars of an Integrated Pest Management (IPM) program.
Had the lady beetles (biological) not done the job, in the interest of domestic bliss, I could have applied a digital pest management tactic by squashing adult magnolia scale females (cultural) or I could apply a systemic insecticide (chemical) later this season to target the scale crawlers while preserving the lady beetles. The overarching goal with IPM is to avoid applying tactics that interfere with or undo one another.
I could not identify the Sigil lady beetle larvae when I posted my June 17th BYGL Alert. However, as I noted in the Alert, the larvae are truly wolves in sheep’s clothing. They have distinctly segmented bodies cloaked in cottony white wax.
In a twist on “you are what you eat,” the larvae resemble mealybugs that are on this lady beetle’s menu. Of course, they will also chow down on soft scales as well as a range of soft-bodied insects including aphids.
The larvae are pupating and adults have started to emerge. I’ve noticed that the lady beetle larvae commonly collect in groups on the underside of leaves before they pupate making them very noticeable.
Now that adults are present to aid in making an identification, I believe the lady beetle that massacred my magnolia scale herd is the Signate Lady Beetle, H. signata. The adults are very small measuring around 1/8” in length, but their impact is mismatched to their size. This lady beetle is known to be highly aggressive against oak lecanium (Parthenolecanium quercifex). However, you must examine plants closely to find the diminutive beetles even as they spirit away astonishing numbers of prey.