March/April 2023 - 17

" They feed on other plants as well, like vegetable
crops and certain weeds, " said UC-Riverside researcher
Houston Wilson. " Some growers have had experiences
where neighboring open fields have grasses that will be
mowed or dried out or killed, and they'll see a flush of
leaffooted bugs move into their orchards. "
Methods for monitoring leaffooted bugs are currently
limited. Right now, canopies are sampled with a beating
tray - placing a tray underneath and hitting the canopy
to see what falls out. This method is time- and laborintensive,
and there aren't established recommendations
for sampling, such as how many trees, how often or what
constitutes a large enough infestation to require treatment.
Decisions frequently are made based on signs of
damage - looking at the nuts and checking to see if there
is gummosis. While gummosis can be caused by a number
of things, if the nut is cut open and shows signs of
penetration of the bug's mouth parts, this verifies that the
damage was caused by leaffooted or related plant bugs.
" It's problematic because it's all after the fact, " Wilson
said. " And we currently don't have a recommendation
of how many damaged nuts is a threshold for making a
decision about treatment. "
When growers see damage, they're going to spray,
Wilson said, but it's often with historical knowledge
working in their favor because some orchards become
infested year after year. Previous observations keep some
growers alert to problematic fields.
But growers can miss these pests
because bugs can move into an
orchard very quickly. Every year,
Extension and pest control advisers
receive calls from growers who get
inundated unexpectedly.
" And when there's that much
damage to the nuts, they fall from
the tree, and that's going to have an
impact on yield, " Wilson said. " For
these reasons, we needed a new tool
for monitoring. "
With these species groups, the
males emit a pheromone that attracts
females, along with other chemicals
used in defense and those produced
during courtship and mating.
With this information, researchers
needed to do two things: 1) identify
and develop a pheromone lure, and
2) build a trap to put it in. But they
faced a Catch-22. How do they test
which trap is best if they do not yet
have an attractant lure to put in it?
And conversely, how would they test
lures if they don't have a good trap?
" We did some work early on in
some highly infested orchards where
we put out different trap types that
might be suitable for this type of insect. And we were
able to generate some clear data that a particular type
of trap was effective, " said Wilson, whose team also
evaluated trap colors and Teflon-based lubricants that
make the traps more slippery so that the insects fall in.
The optimal trap was found to be a cross-vane hanging
panel trap. These traps can be hung in the orchard, and
when an insect lands on a lubricant-coated trap, it falls
into liquid in the trap bottom and drowns.
Adult and nymph
The science of pheromones
Professor Jocelyn Millar, supervisor of a laboratory
in the Department of Entomology at UC-Riverside, and
his lab members captured the pheromone being emitted
by sexually mature male bugs and analyzed it with a gas
chromatograph- mass spectrometer (an instrument that
* Accurately and rapidly sorts nuts by size
* Proven in use for walnuts, pecans and chestnuts
* Video available at:
1709 Hwy 81 S, P.O. Box 311, Grafton, N.D. 58237
Phone: (701) 352-0480 * Fax: (701) 352-3776
Web site: * E-Mail:

March/April 2023

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