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HOUSEHOLD AND STRUCTURAL INSECTS
Cold Tolerance of Bed Bugs and Practical Recommendations for
Control
JOELLE F. OLSON,
1,2
MARC EATON,
1
STEPHEN A. KELLS,
1
VICTOR MORIN,
3
AND CHANGLU WANG
4
J. Econ. Entomol. 106(6): 2433Ð2441 (2013); DOI: http://dx.doi.org/10.1603/EC13032
ABSTRACT Bed bugs were exposed to freezing temperatures for various exposure times to deter-
mine cold tolerance and mortality estimates for multiple life stages. The mean supercooling point for
all bed bug life stages ranged from ⫺21.3⬚Cto⫺30.3⬚C, with the egg stage reporting the lowest value.
A probit analysis provided a lower lethal temperature (LLT
99
)of⫺31.2⬚C when estimates from all
life stages were combined, demonstrating that all stages of bed bugs are not capable of surviving
temperatures below body freezing and are therefore freeze intolerant. At conditions above the LLT
99
,
bed bug mortality depended on temperature and exposure time at temperatures above LLT
99
. Based
on our model estimates, survival was estimated for temperatures above ⫺12⬚C even after 1 wk of
continuous exposure. However, exposure to temperatures below ⫺13⬚C will result in 100% mortality
in d to ensure mortality of all life stages. Unfortunately, sublethal exposure to lower temperatures did
not prevent subsequent feeding behavior in surviving stages. Practical recommendations for man-
agement of potentially infested items are discussed.
KEY WORDS freezing, bed bug, supercooling point, cold tolerance, nonchemical control
Bed bugs (Cimex lectularius L.) are a signiÞcant pest
of humans and domestic animals. Changes in tradi-
tional pest management practices, insecticide resis-
tance, increased international travel, and lack of pub-
lic awareness may have attributed to the recent global
resurgence of bed bugs (Pinto et al. 2007, Potter et al.
2010). Although bed bugs are not recognized as a
disease vector, continuous human exposure may result
in depression, anxiety, lack of sleep, and increased
sensitivity to their bites (Goddard and deShazo 2009,
Reinhardt et al. 2009). Immediately after feeding, bed
bugs seek harborage areas within furniture, personal
belongings, or other areas near host resting sites to
digest the bloodmeal (Usinger 1966). Thus, relocation
of used furniture and other personal belongings facil-
itates the spread of bed bugs throughout society.
Bed bugs cause a substantial economic impact on
the affected persons, the lodging industry, property
owners, and social and emergency services because of
the high costs associated with effective control mea-
sures (Miller 2007). Currently, infestations are con-
trolled by conducting frequent inspections either vi-
sually, with the aid of monitoring devices or detection
by trained canines; laundering; applying steam; heat
treatments; and repeated applications of insecticides
in areas where bed bugs harbor (Potter et al. 2011).
Recent reports demonstrating resistance to pyre-
throid insecticides (Moore and Miller 2006, Romero et
al. 2007, Steelman et al. 2008) and restrictions on
indoor insecticide applications highlight the impor-
tance of an effective integrated pest management
(IPM) program. An IPM program for bed bugs should
include both chemical and nonchemical means for
control.
Extreme temperatures have been used to control
insect pests in structures and stored products for de-
cades (Fields 1992, Denlinger and Lee 1998). Heat
treatments in particular have been used to control bed
bug infestations with reported success (Usinger 1966,
Pereira et al. 2009, Kells and Goblirsch 2011). Struc-
tural heat treatments require special equipment and
trained personnel to ensure thorough and safe appli-
cations of lethal temperatures (White 2010). Heating
equipment used to control bed bugs can be expensive
and in some cases, high temperature treatments may
degrade or damage equipment or affect protective
ratings, such as personal protective equipment used by
ÞreÞghters, which should not be subjected to tem-
peratures ⬎40⬚C during cleaning steps (National Fire
Protection Association [NFPA] 2008). Unfortunately,
persons most at risk of encountering bed bugs include
multifamily housing residents, health care profession-
als, social workers, emergency management services,
and so on (Potter 2012). Thus, alternative control
options are needed for professionals and the general
public involved with control and prevention of bed
bugs.
1
Department of Entomology, University of Minnesota, 219 Hodson
Hall, 1980 Folwell Ave., Saint Paul, MN 55108.
2
Corresponding author, e-mail: Þli0030@umn.edu.
3
Ecolab Research Center, Pest Elimination Division, Ecolab, 655
Lone Oak Dr., Eagan, MN 55121.
4
Department of Entomology, Rutgers University, 93 Lipman Dr.,
New Brunswick, NJ 08901.
0022-0493/13/2433Ð2441$04.00/0 䉷2013 Entomological Society of America
Exposing bed bug-infested clothing or other small
items to freezing temperatures may be a viable control
option for people at risk of bed bug infestations. How-
ever, information pertaining to the cold tolerance of
bed bugs is limited. Benoit et al. (2009) reported 100%
mortality when female bed bugs were exposed di-
rectly to ⫺16⬚C for 1 h. Naylor and Boase (2010)
recommended exposure to ⫺17⬚Cfor2htocontrol
both adults and egg stages. Furthermore, contrasting
reports recommend exposing bed bug-infested items
to temperatures below freezing for at least 2 wk to
ensure mortality of all life stages embedded within
semiinsulated materials (Potter et al. 2007). More ac-
curate recommendations for freeze treatments would
beneÞt professionals and the general public.
For practical applications, determination of freeze
tolerance parameters for all life stages is critical. Two
common cold-hardiness strategies used by insects for
surviving subzero temperatures include freeze intol-
erance and freeze tolerance (Salt 1961, Baust and
Rojas 1985, Zachariassen 1985, Bale et al. 1989).
Freeze-intolerant species generally attempt to protect
themselves from freeze injury by lowering the freez-
ing point of body ßuids (i.e., supercooling; Bale et al.
1989). Freeze-tolerant species permit freezing of tis-
sues, but prevent injury through a variety of mecha-
nisms (Teets and Denlinger 2013). Evaluating the su-
percooling point (SCP), and lower lethal temperature
(LLT), provides information on freeze tolerance of
the target organism (Denlinger and Lee 1998). The
SCP measures the temperature at which body tissues
freeze, while the LLT evaluates animal survival at
short-term exposures to a given temperature. In ad-
dition to providing information on freeze tolerance,
the SCP and LLT provide initial parameters to further
explore exposure time as it relates to lethal tempera-
tures.
For this study, the SCP and LLT were evaluated for
all life stages of bed bugs, as well as their potential to
feed postexposure to sublethal temperatures. In ad-
dition, the relationship between temperature, time,
and mortality was explored using a response surface
experiment and a prediction model was developed for
practical control recommendations. Finally, our
model was compared with actual mortality data col-
lected from bed bugs exposed to a variety of general
house-hold freezers. These Þndings provide clear rec-
ommendations for the appropriate combinations of
temperature and time required to freeze items poten-
tially infested by bed bugs.
Materials and Methods
Insects. Bed bugs were obtained from stock cultures
of the ECL-05 Cimex lectularius L. Þeld strain (Olson
et al. 2009) unless noted otherwise. Colonies were
maintained under standard conditions of 25⬚C and a
photoperiod of 14:10 (L:D) h in 16 oz glass jars with
folded pieces of Þlter paper (Fisher 9.0 cm) for har-
borage and egg deposition. Jars were covered with
fabric (Precision Woven Nylon Mesh 193 ⫻193, Mc-
Master Carr, Chicago, IL) with a pore size of 0.08
m
for ventilation and containment. Colonies were fed
weekly using a method similar to Montes et al. (2002)
with soon-to-expire stocks of human blood (1 U of
Type A red blood cells and1Uofplasma reconstituted
to 600 ml of whole blood) obtained from the American
Red Cross (St. Paul, MN). For the experiments listed
below, “fed”bed bugs had received a bloodmeal to
repletion immediately before exposure and “unfed”
bed bugs were starved at least 7Ð14 d before exposure.
Experiment I: SCP. The objective of this experi-
ment was to determine how SCP varies by fed status
and life stage. Surface-contact thermometry was used
to establish SCPs following methods of Carrillo et al.
(2004). Both fed and unfed adult, Þfth and fourth
instars (n⫽24) were individually attached to 24 gauge
copper-constantan thermocouples coated with a thin
layer of high-vacuum grease (Dow Corning, Dow
Corning Corporation, Midland, MI). Because of their
reduced mass, third, second, Þrst instars and eggs were
attached to a 40 gauge copper-constantan thermocou-
ple. Bed bugs were suspended on the thermocouples
inside the center of polystyrene cubes (19 by 19 by 19
cm) with internal temperatures at 0⬚C and cooled at
a rate of ⫺1.0⬚C/min by placing the cube into a ⫺80⬚C
freezer (Revco model ULT790Ð5-A31 Kendro Labo-
ratory Products, Asheville, NC). Bed bug tempera-
tures were recorded at a frequency of 9.1 Hz with a
multichannel data logger (Personal Daq/56 data ac-
quisition system; Iotech, Inc., Cleveland, OH). To
measure SCP, temperatures were recorded to deter-
mine the lowest point before the exotherm, which is
a slight rise in temperature indicating release from
latent heat of fusion, on an otherwise decreasing tra-
jectory (Lee et al. 1992). After the release of heat, the
temperature recorded by the thermocouple continues
to drop until the thermocouple reaches the lowest
temperature in the freezer.
Eggs were tested at two ages, with “young eggs”
deposited by females within 48 h before exposure and
“old eggs”deposited 3Ð6 d earlier. Eggs were left
attached to Þlter paper to reduce risk of chorion dam-
age. For accuracy purposes, individual bed bugs and
eggs were grouped by Stage and Fed status, but the
group order was randomized to avoid frequent ther-
mocouple changes, mixing of thermocouples con-
nected to the data logger, and repeated recalibration
of the thermocouple sensors. The SCP results were
tested for outliers via the maximum normed residual
test for outliers (Snedecor and Cochran 1989). Anal-
ysis of variance (ANOVA; Proc GLM) was used to
detect differences for the main effects of Stage and
Fed Status and their interaction. Mean SCPs were
compared by LSMEANS using TukeyÐKramer adjust-
ment (SAS Institute 2009) and reported as means and
95% CIs.
Experiment II: LLTs. This experiment measured
mortality across all stages with short-term exposures to
LLTs to determine freeze tolerance of bed bugs when
compared with SCP values. Individuals of all stages,
including both fed and unfed bed bugs, young and old
eggs, resulted in a total of 4,320 bed bugs used (n⫽16
bug stages, 10 bugs per stage, 9 temperatures, and 3
2434 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 6
replicates). To evaluate natural mortality, bed bug
cohorts were randomly assigned to 24⬚C during as-
signment of cold exposure treatments; estimating nat-
ural mortality consisted of 320 bugs (16 stages, 10 bugs
per stage, and 2 replicates). Bed bugs were transferred
into 5-ml plastic vials with a plastic screw-top cap and
with an 8-mm hole drilled into it. Filter paper was Þt
under the cap to prevent escapes and allow for ven-
tilation. Eggs were set up in a similar manner and
collected as previously described. Temperatures
within the vials were recorded with a 24 gauge copper-
constantan thermocouple (Eaton and Kells 2011). For
each exposure, vials containing speciÞc Stages and Fed
Status were randomly assigned to temperatures: 0, ⫺5,
⫺10, ⫺15, ⫺20, ⫺25, ⫺30, ⫺35, and ⫺40⬚C. Similar
vials containing bugs for controls were randomly as-
signed throughout the trials and maintained at 24⬚C.
Vials were placed in the center of polystyrene cubes
(0.35
3
m
3
) with a starting temperature of 0⬚C and were
cooled at a rate of 0.3Ð0.4⬚C/min. Vials were removed
when the target temperature was achieved and im-
mediately placed into slowly elevating temperatures
(i.e., ⫺25⬚C, ⫺15⬚C, 0⬚C, and 5⬚C, 10 min each) to
acclimate the bed bugs back to room temperature
(24⬚C). Bed bugs were relocated to plastic Petri dishes
(50 by 9 mm, Falcon 35 1006, Becton Dickinson Lab-
ware, Franklin Lakes, NJ), with Þlter paper (Fischer
ScientiÞc, P5) and fabric mesh for ventilation. Adult
and nymph mortality was assessed 24 h postexposure
by gently agitating the bug with a forceps to observe
movement. Unassisted movement of any appendage
during the assessment period was reported as survival.
Egg mortality was observed every 24 h for a minimum
of 10 d. Remaining nonhatched eggs were considered
dead 10 d after the last egg in that Petri dish had
hatched. Analysis of the LLT was conducted using a
Proc Probit with a logistic distribution option (SAS
Institute 2009). This method enabled us to assess pro-
portion mortality against temperature and calculate
LLT
50,99
estimates by stage and their associated 95%
CIs.
Seven days postexposure, surviving stages were
combined by temperature treatment and offered a
warmed blood diet using a modiÞed artiÞcial feeding
system to evaluate sublethal effects on feeding behav-
ior. The modiÞed system consisted of a 16-ml plastic
test tube that contained 1Ð2 ml of blood warmed in a
warm-water bath then covered with stretched Para-
Þlm (Alcan Packaging, Peachtree City, GA). The test
tube was inverted over the screened dish containing
the bed bugs on Þlter paper. Bed bugs were allowed
15 min to climb the Þlter paper harborage to reach the
bloodmeal and feed. The data were analyzed by
ANOVA (Minitab 2010) and reported as mean per-
cent fed.
Experiment III: Estimated Mortality Based on
Temperature and Exposure Time. The relationship
between temperature and time was expected to be
nonlinear based on the previous results from Exper-
iment II. Therefore, a Central Composite Design
(CCD) with 21 combinations of temperature and time
was generated by Design Expert version 8.0.1 to ex-
plore the relationship between temperature and ex-
posure time on bed bug mortality. The temperature
inputs were bound by ⫺30⬚C as the lower estimate and
0⬚C as the upper estimate based on the LLT data.
Exposure times were bound for practical reasons by 2
and 168 h. The CCD design used the axial inputs
(⫺30⬚C, 0⬚C; 2 h, 168 h), identiÞed two additional
factors (⫺25⬚C, ⫺5⬚C; 26 h, 144 h) and a center data
point (⫺15⬚C; 85 h) to produce 21 total combinations
of temperatures and times necessary to create the
model. SpeciÞed temperatures (within 2Ð4⬚C) were
achieved using temperature control cabinets (Percival
ScientiÞc, model: 130BLL, Perry, IA) or Styrofoam
boxes (25 cm
3
, 3 cm thick) placed in a Gibson (model:
FV21M2WKFA; Appliance Corporation, Greenville,
MI) freezer. Temperatures were monitored using cal-
ibrated HOBO data loggers model #U23-002 (Onset
Computer Corporation, Bourne, MA).
Groups of 20 eggs (0Ð7 d old), Þrst instars, Þfth
instars, males, and females (both fed and unfed stages)
were exposed to each predetermined combination of
temperature and exposure time. Adults, nymphs, and
eggs were placed separately into modiÞed Petri dishes
as previously described and cooled (5⬚C, then 0⬚C; 10
min each) before placement in each freezer and
slowly warmed (0⬚C, then 5⬚C; 10 min each) before
removal. Eggs remained attached to the original Þlter
paper during both the exposure and the recovery
periods.
A second CCD and set of mortality data were gen-
erated to conÞrm the initial model estimates. The
second CCD design included axial inputs (⫺12⬚C,
⫺20⬚C; 24 h, 96 h based on the previous CCD results),
identiÞed two additional inputs (⫺13⬚C, ⫺19⬚C;
34.5 h, 85.5 h), and a center data point (⫺16⬚C; 60 h)
to produce another 21 combinations of temperature
and time treatments. The previous CCD analysis
showed differences in mortality estimates between
eggs and other life stages, but not fed status. Therefore,
only eggs and unfed Þrst instars were used in the
second CCD to limit the number of treatments. For
the second CCD data set, unfed Þrst instars and eggs
(0Ð7 d old) were housed in 1.5-ml centrifuge tubes
(Fisher, Pittsburg, PA) and placed within an alumi-
num heating block (described in more detail by Eaton
and Kells 2011) to maintain precise temperature set-
tings (within 1Ð2⬚C) throughout the duration of the
experiment.
Mortality for adult and nymph stages was assessed
24 h postremoval from the freezer. Egg mortality was
recorded as the percent of un-hatched eggs 1 wk
postexposure. The data were analyzed by ANOVA and
a Tukey multiple comparison test was performed to
determine signiÞcant differences between life stages
and fed status using a general linear model in Minitab
16 (Minitab 2010) on arcsineÐsquare-root transformed
mortality data. Estimated mortality was plotted as a
function of temperature and exposure time.
Experiment IV: Actual Mortality Using Standard
Household Freezers. The objective of this experiment
was to compare our model estimates to actual bed bug
mortality using general household freezers. Three
December 2013 OLSON ET AL.: LOW TEMPERATURE CONTROL OF BED BUGS 2435
standard household freezers were used in our analy-
sis including a Whirlpool (model: ET18PKXGW01;
Whirlpool USA, Benton harbor, MI), a GE (model:
GTS18TBSAWW; General Electric Company, Louis-
ville, KY), and a Kenmore (model:253.21111103; Sears,
Roebuck and Co., Hoffman Estates, IL). Each freezer
was maintained under normal use conditions (with at
least one-half of the space Þlled and the freezers were
opened several times each day) during the experi-
mental period. Freezer temperatures were recorded
using HOBO data logger models #UA-002-08 or #U23-
002 (Onset Computer Corporation, Bourne, MA) ev-
ery 10 min for the duration of the study.
A susceptible laboratory strain (Fort Dix) from Rut-
gers University was used for this experiment. Previous
results showed that fed status did not have a signiÞcant
impact on mortality; thus, bugs were fed 7Ð21 d before
the experiment using an artiÞcial feeding system sim-
ilar to the one previously described. Groups of Þve
adults and Þve (third to Þfth) instars were placed into
each 3.7 cm in diameter and 1.25 cm tall Petri dish. Five
replicate dishes were prepared for each exposure pe-
riod, wrapped together in a thick cotton sock and
placed within a 1-gallon plastic bag. Five sets of dishes
were placed in each freezer, and one dish was taken
out of each bag 1, 2, 3, and 5 d postexposure. Control
dishes were set up the same and exposed to room
temperature throughout the duration of the experi-
ment. Immediately postexposure, the cotton sock was
removed and all dishes were exposed to room tem-
perature conditions. Mortality for each set of bugs was
examined as described above 24 h postremoval from
the freezer. Mean mortality and freezer conditions
including mean, SE, and range were calculated and
analyzed in Minitab 16 (Minitab 2010).
Results
Experiment I: SCP. The main effect of Stage was
signiÞcant (F
8,324
⫽44.19; P⬍0.0001), but not the
main effect of Fed Status (F
1,324
⫽1.33 ⫻10
⫺3
;P⫽
0.9709). The interaction of Stage and Fed Status was
signiÞcant (F
6,324
⫽7.30; P⬍0.0001). A review of
simple effects showed that Fed Status was only sig-
niÞcant among Þrst instars; thus, SCP estimates for fed
and unfed individuals were combined for the remain-
ing life stages (Fig. 1). The youngest stages provided
the lowest SCPs, with no signiÞcant differences (P⬎
0.4139) between young eggs at ⫺30.3⬚C (95% CI ⫽
⫺30.7, ⫺29.8), old eggs at ⫺28.1⬚C(⫺28.7, ⫺27.5), and
un-fed Þrst instars at ⫺28.4⬚C(⫺29.29, ⫺27.51). In-
terestingly, SCP increased signiÞcantly (P⫽0.0002)
postfeeding by Þrst instars to ⫺25.0 (⫺26.2, ⫺23.7)⬚C.
The SCPs of males (⫺24.3 [⫺25.4, ⫺23.2]⬚C) and
females (⫺22.4 [⫺23.3, ⫺21.5]⬚C) were signiÞcantly
different from each other (P⫽0.0075), but there were
no signiÞcant differences in SCP estimates between
second through Þfth instars and females (P⬎0.1603).
The SCPs for males were not signiÞcantly different
from Þrst-instar fed nymphs, fourth, and Þfth instar
nymphs (P⬎0.1526; Fig. 1).
Experiment II: LLT. The effect of short-term ex-
posure to lower temperatures resulted in two signif-
icantly different LLT
99
estimates for eggs compared
with all other bed bug life stages (Fig. 2). Preliminary
analysis by stage of slope and intercept estimates and
Fig. 1. SCPs for males, females, nymphs, and eggs. For
stages other than eggs and Þrst instar nymphs, the SCP values
for fed and unfed bed bugs were combined. Mean SCP (⫾
95% CI) are displayed for each life stage. Different letters
denote statistical difference among means (
␣
⫽0.05).
Fig. 2. Mean percent mortality (OO)⫾95% CI (OO)
of C. lectularius for eggs (top) and combined stages of adults and
nymphs (bottom) subjected to short-term exposures to LLTs.
The Logistic regression characteristics are Logit(pˆ)⫽
⫺1.8081 ⫺0.1473⫻for eggs and Logit(pˆ)⫽⫺6.2172 ⫺0.3782⫻
for the adult and nymphal stages.
2436 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 6
their related 95% CIs indicated similarity in mortality
curves that enabled formation of these two groups.
Data for both young and old eggs were combined and
resulted in a slope estimate of ⫺0.1473 (95% CI ⫽
⫺0.1939, ⫺0.1006) and LLT
99
of ⫺43.5⬚C(⫺58.0,
⫺35.9⬚C). All other life stages combined resulted in an
estimate of ⫺0.3782 (⫺0.2552, ⫺0.5013) and LLT
99
of
⫺28.6⬚C(⫺34.8, ⫺25.3⬚C). The goodness-of-Þt test
from the Probit (logistic) analysis was signiÞcant (P⬍
0.0001), and variances were multiplied by a hetero-
geneity factor for both. For eggs, CIs were calculated
using a tvalue of 2.01, and the analysis for other stages
incorporated a tvalue of 1.97 (PROC Probit, SAS Insti-
tute 2009). Despite excess variability in mortality at sub-
lethal temperatures, the data did not show a systematic
departure from the model estimates. Average natural
mortality across all treatments was ⬍3.0%.
Owing to the relatively few survivors at some of the
cooler temperatures, life stage, and prior fed status was
ignored in the following analysis. The percent of bed
bugs that fed postexposure to 0.0, ⫺5.0, ⫺10.0, ⫺15.0,
and ⫺20.0⬚C did not differ signiÞcantly from the con-
trol group (F
5, 192
⫽1.54; P⫽0.18; Fig. 3). Regardless
of exposed temperature, a minimum of 71.77% of the
bed bugs fed postexposure to sublethal temperatures.
Thus, sublethal exposure to freezing temperatures did
not affect the surviving bugsÕ ability to forage and feed.
Experiment III: Estimated Mortality Based on
Temperature and Exposure Time. Excluding eggs,
there were no signiÞcant differences in mortality es-
timates between fed and unfed life stages (P⫽0.40).
In addition, there was no signiÞcant difference be-
tween estimated mortality of adults and nymphs (P⫽
0.08); thus, the data for these life stages were com-
bined (Fig. 4A) into a single surface plot showing
estimated bed bug mortality for various combinations
of temperature and exposure times. Predicted esti-
mates for egg mortality varied slightly indicating that
eggs are more susceptible to colder temperatures com-
pared with other life stages, when time is included as
a factor (Fig. 4B). Both models were statistically sig-
niÞcant, with adults and nymphs (P⬍0.001; R
2
⫽
0.997) and eggs (P⬍0.001; R
2
⫽0.849). However, the
difference between egg mortality estimates and the
other life stages may be attributed to natural mortality
of the egg stage. On average, 20% of eggs in the control
groups did not hatch. Therefore, the arc-sin square
root percent mortality model for adults and nymphs
provides the best estimate of bed bug mortality for all
life stages and is deÞned as:
Y (arc-sin square root proportion mortality) ⫽
⫺0.51 ⫹[(4.41 ⫻10⫺4)⫻Temp] ⫹
[(2.24 ⫻10⫺2)⫻Time] ⫹[(⫺1.22 ⫻10⫺3)⫻
Temp ⫻Time] ⫹[(2.82 ⫻10⫺3)⫻
Temp2]⫹[(⫺1.69 ⫻10⫺4)⫻Time2]⫹
[(⫺6.85 ⫻10⫺5)⫻Temp2⫻Time] ⫹
[(⫺4.65 ⫻10⫺6)⫻Temp ⫻Time2]
Fig. 3. Mean percent fed (⫾95% CI) of surviving C.
lectularius 1 wk postexposure to LLTs. Bolded numbers
above each bar indicates the number of individuals surviving
the freezing conditions and used in the feeding trial.
Fig. 4. Response surface plots showing predicted percent mortality relative to temperature (⬚C) and exposure time (h)
for (A) adults and nymphs and (B) eggs of C. lectularius.
December 2013 OLSON ET AL.: LOW TEMPERATURE CONTROL OF BED BUGS 2437
The second CCD experiment performed with Þrst
instars and eggs only validated the initial CCD exper-
iment with both models in agreement in terms of the
signiÞcant factors and their coefÞcients (R
2
⫽0.741;
P⫽0.001). Based on the equation above, temperatures
higher than ⫺12⬚C are not practical for effective con-
trol measures against bed bugs. A minimum exposure
time of 85 h at ⫺15⬚C is required for 100% mortality of
all life stages and exposure time decreases for tem-
peratures below ⫺16⬚C.
Experiment IV: Actual Mortality Using Standard
Household Freezers. The average daily temperature
for each freezer was consistent at ⫺13.7⬚C, but fre-
quent warming, cooling, and defrost cycles resulted in
bugs being exposed to a broad range of temperatures
(Table 1). Even on the warmest temperature setting,
there was a large ßuctuation in daily temperatures
resulting in a relative SD of 14.5Ð15.9%. Thus, each
group of treated bugs may have been exposed to tem-
peratures as low as ⫺24⬚C during the Þrst day. There
were signiÞcant differences (P⬍0.001) in bed bug
mortality between the freezer-treated bugs and the
controls after only 24 h exposures (Table 1). Similar
mortality rates (100%) were recorded for each freezer
at 2, 3, and 5 d (data not shown).
Discussion
This study found that bed bugs were less susceptible
to freezing temperatures than previously reported.
Benoit et al. (2009) reported ⫺16⬚C for 1 h; and Naylor
and Boase (2010) referenced ⫺17⬚Cfor2h.Inour
study, bed bugs survived lower temperatures, with
eggs surviving in short-term exposures (LLT) to tem-
peratures as low as ⫺25⬚C (Fig. 2). When time was
considered, 100% mortality of bed bugs occurred after
80hat⫺16⬚C (Fig. 4). Differences in results may be
attributed the source of blood used. The two studies
referenced above used rabbit or chicken blood, and
this study used human blood. Differences in results
may also be attributed to the slower rates of cooling
and warming that bed bugs were subjected to in this
study. While Naylor and Boase (2010) illustrate a
cooling rate between ⫺0.5⬚C/min and ⫺0.13⬚C/min
(approximately), both studies, including Benoit et al.
(2009), restored bed bugs to room temperature with-
out intermediate warming steps. In our study, bed
bugs were temporarily exposed to intermediate tem-
peratures of 0 and 5⬚C before freeze treatments and
again after treatment before placement into room
temperature conditions.
In freezing studies, precooling and postwarming
rates can affect survival (Bale 1987, Bale et al. 1989),
and brief exposures to chilling or intermediate freez-
ing conditions can elicit a variety of protective re-
sponses in insects resulting in rapid cold hardening
(Czajka and Lee 1990, Chen and Denlinger 1991). In
practical applications, equipment type, insulative
properties of items being frozen (Strang 1997), and
postfreezing handling procedures can affect the rate
of cooling and warming items. Our study evaluated
freeze tolerance and mortality using a temperature
proÞle that would likely be encountered during prac-
tical application of low temperature treatments. In the
future, evaluating different cooling and warming rates
may help further reÞne the models and improve prac-
tical recommendations for nonchemical control of in-
sects.
The LLT mortality shows high variability resulting
in a correction factor added to the estimate of the 95%
CIs. This type of variability has previously occurred in
nonchemical control with mold mites (Eaton and
Kells 2011) and webbing clothes moths (Brokerhof et
al. 1992). This variability may be a factor of target site
nonspeciÞcity of cold injury and the diversity of phys-
iological, biochemical, and gross anatomical systems
that may be affected by cold temperatures as de-
scribed in more detail by Teets and Denlinger (2013).
Although it is common to graphically present data as
a mean and SEM, presenting data from the raw trials
in this form illustrates the risks of not properly achiev-
ing critical conditions for insect mortality.
Freezing potentially infested items from museum
collections or stored food commodities has been a
common pest management practice for several de-
cades (Strang 1992). Recommendations for manage-
ment of museum and stored product pests are vauge,
suggesting temperatures treatments below ⫺20⬚C for
several minutes or up to 1 wk (Strang 1997, Fields
1992). According to our results, temperatures below
⫺15⬚C are sufÞcient to control all life stages of bed
bugs after only 3.5 d; and temperatures below ⫺20⬚C
require ⱕ48 h. Thus, our results provide more accurate
and precise recommendations for nonchemical con-
trol of bed bugs using freezing temperatures.
Bed bugs feed every 2.5 d on average, but it may be
weeks and even months between available bloodmeals
(Reinhardt et al. 2010). Therefore, the amount of
blood in the insect gut can vary substantially in Þeld
populations. However, fed status had no impact on
cold tolerance or mortality estimates of bed bugs. This
was surprising because insect diet and gut contents
have inßuenced cold tolerance parameters of several
other insect species (Salt 1953, Carrillo and Cannon
2005). It is likely that the bloodmeal did not synergize
ice nucleation as temperatures declined and this re-
Table 1. Standard operating conditions and mean mortality of C. lectularius after 24-h exposure to three common household freezers
Brand Operating conditions (⬚C) % mortality after 24 h
Mean SE Range Defrost cycles/d Treated ⫾SE Control ⫾SE
Kenmore ⫺13.7 0.05 (⫺3.4, ⫺24.1) 14 100.0 ⫾0.0 2.0 ⫾0.0
Whirlpool ⫺14.2 0.05 (⫺7.3, ⫺21.1) 18 100.0 ⫾0.0 0.0 ⫾0.0
GE ⫺15.1 0.04 (⫺10.8, ⫺19.5) 19 100.0 ⫾0.0 0.0 ⫾0.0
2438 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 6
sulted in no observable differences in SCP, LLT, and
mortality estimates based on fed status. For control
purposes, it is important to note that fed status of bed
bugs does not signiÞcantly impact cold tolerance or
freezing recommendations.
Some insects have developed a variety of behav-
ioral, physiological, and biochemical adaptations to
survive freezing (Storey and Sorey 1996). However,
based on the SCP and LLT estimates reported here
and by Benoit et al. (2009), bed bugs are not freeze
tolerant because LLT mortality data were within
the 95% CI for the SCP estimates (Lee et al. 1992).
Freeze tolerance would have been suspected if the
SCP was substantially higher than the LLT estimates
(Bouchard et al. 2006) or if a signiÞcant proportion of
individuals survived temperatures below the SCP es-
timate (Eaton and Kells 2011).
If lethal temperatures and exposure times are not
maintained during the control period, surviving stages
are capable of feeding posttreatment (Fig. 3). Al-
though this study did not evaluate physical damage to
the integument or posttreatment effects on reproduc-
tive behavior, bed bugs offered a bloodmeal were
required to climb a short distance to initiate feeding;
thus, host-seeking behavior remained intact. Acquir-
ing a bloodmeal on a regular basis is important for
survival, development, and reproduction of bed bugs
(Mellanby 1939, Davis 1955, Reinhardt and SivaÐJothy
2007). Thus, failure to maintain lethal combinations of
temperature and exposure time during the freezing
process may result in continuity of the pest activity
and development.
There were signiÞcant differences in bed bug mor-
tality recorded from the freezer exposures compared
with our model estimates. The exposure time differ-
ence between estimated and actual mortality (3.5 vs.
1dat⫺14⬚C) is unlikely attributed to differences
between C. lectularius strains and more likely caused
by large ßuctuations in operating temperatures caused
by the automatic defrost cycles in the domestic freez-
ers (Table 1). A difference in cold tolerance estimates
between strains has been reported in Calliphora vicina
RobineauÐDesvoidy, 1830, a species of blow ßy (Hay-
ward and Saunders 1998). However, differences were
attributed to geographical origin of each strain. As a
structural pest that generally reproduces indoors un-
der consistent environmental conditions, the origin of
the strain is unlikely to cause signiÞcant differences in
mortality estimates.
The extremely low temperatures recorded during
the Þrst 24 h in each domestic freezer were likely the
cause for different mortality estimates observed be-
tween our model and the freezer data collected in
Experiment IV. Although our model likely over-esti-
mates the exposure time required for 100% mortality
of bed bugs, our model data were collected under
controlled conditions with restricted ßuctuations in
operating temperatures and, therefore, a more reliable
source for pest management recommendations. Fur-
thermore, our model applies to situations where au-
tomatic defrost cycles may not be installed, such as
commercial freezer equipment. Freezers with large
ßuctuating defrost cycles are generally not recom-
mended for pest control purposes, as temperatures
may rise to levels above freezing for the target insect
pest (Florian 1990). In addition, homeowners inter-
ested in bed bug control methods may not have access
to more sophisticated systems and therefore, should
follow temperature and exposure time estimates pro-
vided by the model.
When alternative control methods are not feasible,
bed bug-infested items can be placed in a freezer to
destroy all life stages. Items suspected of infestation
should be bagged before placement in the freezer to
prevent bed bugs from exiting the items and perishing
elsewhere inside the freezer. Bagging an item before
placing it in a freezer will also protect it against
changes in condensation or damage caused by mois-
ture. Infested items should be placed in the freezer at
⫺17.8⬚C(0⬚F) for a minimum of 3.5 d, though time
may be decreased to 48 h if temperatures average
below ⫺20⬚C. Standard upright household freezers
are typically set to ⫺17.8⬚C(0⬚F) or lower for proper
food storage (U. S. Department of AgricultureÐFood
Safety and Inspection Service [USDAÐFSIS] 2010),
though older equipment may not be capable of main-
taining this temperature. Insulated items may take 1Ð3
additional hours to reach lethal temperatures (Carrlee
2003). An indoor and outdoor thermometer should be
used to verify operating temperatures before and dur-
ing the treatment process.
Acknowledgments
We thank the following students and research assistants:
Derek Hersch, Jake Gibbons, Hao Song, Kevin Olson, and
Logane Kiehnau from the University of Minnesota for their
assistance in bed bug colony maintenance and data collec-
tion. In addition, we thank Roger Moon for recommendations
regarding the statistical design, analysis of the mortality
model, and helpful comments on an earlier version of this
manuscript. This work was funded in part by the Ecolab Inc.,
St. Paul, MN; the Minnesota Pest Management Association;
and the University of Minnesota Agricultural Experiment
Station projects (MN-019) and (MN-050).
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Received 16 January 2013; accepted 5 August 2013.
December 2013 OLSON ET AL.: LOW TEMPERATURE CONTROL OF BED BUGS 2441
