ScienceDaily (June 6, 2009) —
Scientists here have determined that combining bed bugs’ own chemical
signals with a common insect control agent makes that treatment more
effective at killing the bugs.
The researchers found that stirring up the bed bugs by spraying their
environment with synthetic versions of their alarm pheromones makes them
more likely to walk through agents called desiccant dusts, which kill
the bugs by making them highly susceptible to dehydration.
A blend of two pheromones applied in concert with a silica gel
desiccant dust proved to be the most lethal combination to kill bed
bugs.
In the past decade, bed bugs have become an increasing problem in
industries ranging from agriculture and housing to travel and
hospitality, so much so that the Environmental Protection Agency hosted
a National Bed Bug Summit in April of this year.
The species, Cimes lectularius, also is developing
resistance to the insecticides approved to spray infested areas,
treatments that belong to a group of compounds called pyrethroids.
Desiccant dusts that are sprinkled in infested areas, however, are
among the oldest forms of insect control and are still considered
effective killers as long as the bugs walk through them.
“Once we put the alarm pheromone in the places bed bugs hide, boom,
they instantly started moving around and moving through the desiccant
dust,” said Joshua Benoit, lead author of the study and a doctoral
candidate in entomology studying under David Denlinger at Ohio State
University.
“Consistently, the addition of a pheromone blend to desiccant dust
was more effective than adding either chemical by itself or by using
desiccant dust alone.”
The research is published in the current issue of the Journal of
Medical Entomology.
The two bed bug alarm pheromone ingredients are known as
(E)-2-hexenal and (E)-2-octenal. When bed bugs are disturbed or excited,
they secrete these two pheromones and tend to want to move around.
While some pheromones are known to attract species for reproductive
purposes, these particular pheromones act more as a repellent, Benoit
explained.
“These pheromones also can be bought from any chemical company.
They’re well-established chemicals, are easy to make in the lab, and are
readily available,” he said.
Two types of desiccant dusts were used in the experiments:
diatomaceous earth, a naturally occurring, chalky substance, and a
compound called Dri-die, made from a silica gel. Desiccant dusts are
designed to disturb the bed bugs’ cuticle, particularly the waxy outer
layer on insects that allows bugs to stay hydrated. Without the waxy
protection, insects are more prone to dry up and die.
The researchers first tested the chemical combination on five bed
bugs at a time for 10-minute exposures in petri dishes. They tested both
types of desiccant dusts as well as each pheromone component alone and
in a blend more typical of natural secretion.
Bed bugs exposed to Dri-die and a blend of pheromones lost water at a
much faster rate than did bed bugs treated with the desiccant dust
alone. The scientists found that bed bugs exposed to Dri-die alone lost
21 percent more water than untreated control bugs. Water loss nearly
doubled with either (E)-2-hexenal or (E)-2-octenal applied alone and
tripled with a blend of both pheromones.
Young bed bugs exposed to the combination died in about a day, three
days earlier than control bed bugs. Adult female bed bugs exposed to the
combination survived for about 6 ½ days, compared to females exposed
only to the desiccant dust, which lived for an average of 17 days.
In petri dish tests, the scientists found that the combined
treatments using Dri-die consistently worked better than those using
diatomaceous earth at generating rapid water loss in the bed bugs.
Turning to a more natural setting for bed bugs, the researchers set
up a small plastic container in which a folded piece of paper offered
bed bugs a place to hide. Bed bugs tend to stay hidden in wall and floor
cracks, moldings or mattresses by day and feed on human or animal blood
at night. The researchers created this experimental habitat to see if
alarm pheromones would bring bed bugs out of hiding.
After the bed bugs stopped moving within the paper, called a
harborage, the scientists applied the desiccant dust followed by the
alarm pheromone. They used the most effective blend of pheromones as
determined in the petri dish experiments, as well as Dri-die, the more
effective of the two desiccant dusts.
All of the bed bugs came out of hiding within five minutes of the
application of the alarm pheromones, Benoit said. And the combination of
a blend of pheromones and Dri-die reduced survival by 50 percent of both
young and adult bed bugs, he said. At least half the young bed bugs were
dead within 10 days, and about 60 percent of adult female bed bugs died
within 40 days.
“Desiccant dust is messy, but it’s not toxic, so it can be used in
agricultural settings, such as chicken coops, where bed bugs can be a
big problem,” Benoit said. The dust method also can be used in housing,
where it would be sprinkled on carpet and eventually vacuumed.
These results were achieved in small areas, but Benoit and colleagues
hope the technique could also be applied to large environments infested
with bed bugs. Benoit is reluctant to suggest the use of desiccant dusts
with alarm pheromones until additional experiments are conducted.
“Before companies start selling desiccant dusts laced with alarm
pheromones, more tests need to be carried out in room-sized arenas to
determine any possible negative effects,” Benoit said. Even so, the
researchers believe the use of alarm pheromones could increase the
effectiveness of desiccant dusts and other kinds of residual
insecticides used to kill bed bugs as well.
Benoit noted that repeated use of spray pesticides to which bed bugs
are resistant boosts the survival of bed bugs with that resistance,
forcing the use of higher and higher concentrations of toxic chemicals
to eradicate the insects.
“We think that rather than pursue completely new pesticides, it’s
better to use old pesticides in new ways,” he said.
This research was supported by a grant from the National Institute of
Allergy and Infectious Diseases and an Ohio Agricultural Research and
Development Center Director’s Fellowship to Benoit.
The study’s co-authors are Seth Phillips and David Denlinger of Ohio
State’s Department of Entomology, and Travis Croxall, Brady Christensen
and Jay Yoder of Wittenberg University’s Department of Biology.
Journal reference:
- Joshua B. Benoit, Seth A. Phillips, Travis J. Croxall, Brady S.
Christensen, Jay A. Yoder, David L. Denlinger. Addition of
Alarm Pheromone Components Improves the Effectiveness of Desiccant
Dusts Against Cimex lectularius. Journal of
Medical Entomology, 2009; 46 (3): 572 DOI:
10.1603/033.046.0323
