Angewandte
Communications
Chemie
Pheromones Hot Paper
The Sex Attractant Pheromone of Male Brown Rats: Identification and
Field Experiment
Stephen Takµcs, Regine Gries, Huimin Zhai, and Gerhard Gries*
Abstract: Trapping brown rats is challenging because they
avoid newly placed traps in their habitat. Herein, we report the
identification of the sex pheromone produced by male brown
rats and its effect on trap captures of wild female brown rats.
Collecting urine- and feces-soiled bedding material of labo-
ratory-kept rats and comparing the soiled-bedding odorants of
juvenile and adult males, as well as of adult males and females,
we found nine compounds that were specific to, or most
prevalent in, the odor profiles of sexually mature adult males.
When we added a synthetic blend of six of these compounds
Pest-management experts engaged in rat control have
often observed that those traps that have captured a rat are
more likely than new traps to yield another capture,
[18]
possibly because traps with prior captures carry some sort
of rat odor. There is also emerging experimental evidence that
urine odorants from conspecific rodents alleviate bait or trap
shyness, as demonstrated for desert gerbils (Meriones hurria-
[
19]
[20]
nae),
Indian gerbils (Tateri indica),
Gambian giant
and roof rats
[21]
pouched rats (Cricetomys gambianus),
(Rattus rattus). We have recently shown that trap boxes
[22]
[23]
(
2
2-heptanone, 4-heptanone, 3-ethyl-2-heptanone, 2-octanone,
-nonanone, 4-nonanone) to one of two paired food-baited
were most effective in trapping wild brown rats when they
[24]
were baited not only with a food mix and with synthetic rat
pup sound but also with urine- and feces-soiled bedding
material of laboratory-kept brown rats. Combined, all of
these observations imply that specific scent cues or phero-
mone signals could be identified and formulated to enhance
trap captures of rodents.
trap boxes, these boxes attracted significantly more laboratory-
strain female rats in laboratory experiments, and captured ten
times more wild female rats in a field experiment than the
corresponding control boxes. Our data show that the phero-
mone facilitates captures of wild female brown rats.
Some 131 compounds have been identified in the urine
and/or preputial glands of brown rats (Supporting Informa-
tion, Table S1) and inferred or speculated to play a role in
B
rown rats (Rattus norvegicus) are significant global
[
1,2]
[25]
pests.
pathogens,
ishing yields of agricultural crops,
They inflict harm by vectoring disease-causing
[3–5]
[6]
[7,8]
soiling food, spreading allergens,
dimin-
sexual or social interactions. Only nine compounds were
[
3,9]
[25]
endangering island
subjected to some kind of behavioral test. Most of these
[
10]
seabird colonies,
indigenous fauna.
by brown rats in urban centers
and as an invasive species harming
These many adverse effects caused
tests entailed the insertion of “odor-painted” glass rods into
a cage housing a single rat and then recording the ratꢀs sniffing
[
11,12]
[13]
[25]
and in agricultural or
or licking responses. Still, it remained unknown whether
[
14]
ecosystem settings have prompted ongoing efforts to trap
or poison rats, in turn exerting selective pressure on rats to
evolve counter-adaptations. Neophobia (the fear of new
objects) is one such well documented counter-adaptation
that helps rats avoid being trapped. Neophobic rats do not
readily accept or enter new objects such as bait boxes in their
habitat. Yet, tamper-proof trap boxes are mandated in rodent
management as they minimize the risk of accidentally
poisoning pets and humans, and the capture of non-target
male or female brown rats actually produce a sex attractant
pheromone that mediates long-range chemotactic attraction,
and if such a pheromone was produced, whether it would have
a positive, negative, or neutral effect on trap captures of wild
rats in the field.
[15]
Our search for a pheromone took various considerations
into account. We predicted that the components of a sex
attractant pheromone would need to be sufficiently volatile to
attract potential mates over some distance. For that reason,
we opted not to extract odorants or proteins from urine, but
instead to capture the odorants in the volatile headspace
emanating from urine. We further predicted that pheromone
components would be specific to the urine odor of the
producing sex, and would appear only as juveniles become
sexually mature adults. Based on these predictions, we
focused our pheromone search on volatile components
specific to, or most prevalent in, sexually mature rats.
To obtain the urine headspace volatiles of brown rats as
they matured from juveniles to adults, we used four-week old
rats and housed them in the Animal Research Centre of
Simon Fraser University. We kept four groups of five females
each and four groups of five males each in separate cages
lined with corn cob bedding. Rats in randomly assigned
treatment groups, but not in (naive) control groups, had
intermittent opportunity to see and smell rats in opposite-sex
[
16]
animals. The lag time for neophobic rodents to become
accustomed to the presence of trap boxes in their habitat, and
to enter them and get trapped, greatly reduces the expediency
[
17]
of rat control.
[
*] S. Takµcs, R. Gries, H. Zhai, Prof. G. Gries
Department of Biological Sciences
Simon Fraser University
Burnaby, British Columbia (Canada)
E-mail: gries@sfu.ca
H. Zhai
Department of Chemistry
Simon Fraser University
Burnaby, British Columbia (Canada)
6
062
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 6062 –6066