YSM Issue 96.2

FOCUS
Public Health
male fly stayed attached to the dummy for
a prolonged period of time, suggesting that
these compounds also act as arrestants—
halting all motion—to prevent premature
interruption of mating. Clearly, smell
seemed to play a powerful role in mating!
Next, the researchers sought to investigate
cellular mechanisms that may facilitate
the observed behavioral responses.
Removing G. morsitans males’ antennae
eliminated their attraction response,
suggesting that the observed behavioral
responses in mating are facilitated by scent.
Furthermore, research has suggested that
volatile odors are detected via the trichoid
sensilla, a sensory organ located in the
antenna of the fly.
In a method called single-sensillum
electrophysiology, the researchers
obtained recordings of trichoid sensilla
response to odors detected in the air
by antenna. Initially, only MPO elicited
excitatory responses from both sexes, but
particularly from males. After reducing
the distance from which the odor was
delivered, activation in neurons was seen
with MP, MO, and MPO, correlating
with the behavioral results observed
in earlier experiments. However, there
was little to no response in olfactory
neurons to these six compounds in G.
fuscipes, another tsetse species that is
the prominent vector of trypanosomes
in east Africa. This finding suggested
that these pheromones are specific to G.
morsitans mating mechanisms. Indeed,
it was found that G. morsitans males
made no attempt to mate with untreated
G. fuscipes females; however, when G.
fuscipes females were sprayed with MPO,
the males began to engage, suggesting
that MPO may act as an
aphrodisiac, a stimulant
for sexual desire, for G.
morsitans males.
Could Infection Change
Mating?
The last study
examined if these
findings held for
tsetse flies infected
with trypanosomes,
which is the
ultimate target for
traps to prevent
the spread of African sleeping sickness.
There were no changes in single-sensillum
electrophysiology, meaning there was no
change in neuronal response. However,
there were significant behavioral changes
observed in mating.
When paired together, uninfected
virgin female G. morsitans mated with
infected and uninfected males at the same
frequency. However, uninfected virgin
male G. morsitans mated with uninfected
females one hundred percent of the
time over infected females, suggesting
that there may be a compound that
lowers the sexual receptivity of infected
females and acts as a repellent against
G. morsitans males. The group hopes to
further study twenty-one compounds
that were identified in GC-MS as specific
to infected flies. “I'm interested to study
if this compound is produced as a defense
against the parasites,” Ebrahim said.“We
don't know if those compounds were
produced by the tsetse fly in response
to an infection, or maybe they were
produced by the parasites themselves,”
Weiss said.
Harnessing The Power Of Pheromones
The results of the study suggest that
MPO acts specifically as an attractant,
aphrodisiac, and arrestant on G. morsitans
males to activate circuits that mediate
olfactory attraction, sexual desire, and the
halting of movement, respectively. The
usage of MPO in traps holds great promise
from both an environmental and economic
perspective. “Compounds from the fly itself
[…] will be less toxic if we want to use it in
the field compared to other compounds like
DEET,” Ebrahim explained. These natural
ABOUT THE AUTHOR
compounds are also much less expensive
than DEET, which makes implementation
of tsetse fly control more realistic in
developing countries.
In the future, the researchers hope to test
MPO in Kenya with collaborators, who are
currently using tsetse fly host odors such
as cow urine as attractants. “If we combine
MPO with natural host odors, it might
increase the efficiency of control for a trap,”
Ebrahim said. “A more specific odor might
attract more flies and reduce the number
of cases of infection by trypanosomes.”
However, there are challenges
validating field work with lab work, since
the flies in the experiment are different
from those found in a typical African
savanna. In addition, in the real world,
there are many fluctuating and uncertain
factors, according to Ebrahim. Despite
these challenges, the group remains
undeterred, and their passion stays
vibrant. “You will have to be optimistic
and creative for the biggest experiments
you design,” Ebrahim said. ■
CINDY MEI
CINDY MEI is a sophomore in Grace Hopper studying neuroscience. In addition to writing for YSM,
she serves as communications chair on Yale Math Competitions and volunteers with Yale DEMOS
and Yale New Haven Hospital. She also conducts epilepsy and Tourette’s syndrome research at the
Yale School of Medicine.
THE AUTHOR WOULD LIKE TO THANK Shimaa Ebrahim, Brian Weiss, and John Carlson for their
time and enthusiasm in answering questions and providing interactive insight about their research.
FURTHER READING:
Ebrahim, S.A.M., Dweck, H.K.M., Weiss, B.L., & Carlson, J.R. (2023). A volatile sex attractant of tsetse
flies. Science, 379 (6633), doi: 10.1126/science.ade1877
24 Yale Scientific Magazine May 2023 www.yalescientific.org