Page 17 - Free State Summer 2023

New York, where these two boxwood have been heavily
exposed to Cydalima for several months. B. microphylla
var. japonica ‘Winter Gem’ (center page 16) is virtually
completely defoliated. By contrast, B. ‘Green Mountain’
(bottom page 16) remains virtually free of BTM damage.
No webbing, frass, or larvae, could be observed. Less
than 1% of the leaves were dead from various abiotic
conditions. Another 1% of the leaves had been completely,
or partially, eaten by the BTM. It appears in this
environment with heavy omnipresent BTM, they nibbled
(aka “taste tested”) ‘Green Mountain’. They preferred to
pass. The alkaloids of Buxus are well understood. There
are nearly 50 different steroid alkaloids in Buxus. Two are
toxic, buxine and cyclobuxine. Wildlife is fully aware of this
toxicity and do not consume the foliage, or young stems,
of boxwood where these alkaloids are most concentrated.
Perhaps ‘Green Mountain’ has a higher concentration of
these, or other, steroid alkaloids repealing the BTM?

Unchecked, Cydalima can significantly damage and
potentially kill boxwood. It begins by eating the entire
leaf, or skeletonizing it and returning later to consume the
remainder later (right top and bottom). In short order,
Cydalima will eat all the leaves on the boxwood. Once
the larvae have consumed all the boxwood leaves, it is
often reported, “…larvae have been observed feeding on
the bark, which can cause branches or the entire plant
to die.” This is unfortunate and misleading. Personal
observations by the author suggest the larvae only strip
away the bark to feed on the underlaying, nutrient rich,
cambium (top page 18). Note the brown bark at the
bottom of the stem. The two larvae are eating the green
colored cambium. The white portions of the stem are the
wood of the boxwood, absent of all bark and cambium –
the result of the voracious feeding by the larvae.
adult stage also lasts for about two weeks (top right page
Cydalima Life Cycle
19). It has a wing span of about 1¾ inch. The wings are
The BTM overwinters as a larva, in the third instar, inside white with a brown margin. Not shown is an adult variant
a silken cocoon spun between two leaves (top center with brown wings having two small white spots. The
page 18). The webbing can be more extensive and include female will lay 15 to 100 eggs in one mass. The female will
boxwood debris (top right page 18). This “nest building” lay one, occasionally several egg masses.
approach provides the larvae with superior protection Mitigation
and keeps its food (boxwood) immediately available.
The larva has a black head and pale green body. There The USDA, Animal and Plant Health Inspection Service
are two rows of black dots on its back (top left page 19). (APHIS), Plant Protection and Quarantine (PPQ) program,
The sides have white and black stripes which may have has been investigating control tactics for this moth. One
occasional gaps. Then, the pupal stage (top center page of them is benign and environmentally safe, mating
19) lasts for about two weeks. The resulting, non-feeding, disruption that includes the use of the moth’s sex
(continued on next page)

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