Toxicities of Selected Essential Oils, Silicone Oils, and Paraffin Oil against the Common Bed Bug (Hemiptera: Cimicidae)

Abstract

The common bed bug [Cimex lectularius L. (Hemiptera: Cimicidae)] and tropical bed bug [Cimex hemipterus F. (Hemiptera: Cimicidae)] resurged in the United States and many other countries over the past decades. The need for safe and effective bed bug control products propelled the development of numerous 'green insecticides', mostly with essential oils listed as active ingredients. Various inorganic and organic oils also were used for bed bug management. However, there are no published studies on their toxicities against bed bugs. In this study, we screened 18 essential oils, three silicone oils, and paraffin oil (C5-20 paraffins) for their toxicities against bed bugs. All the oils exhibited insecticidal activity in topical assays. Their toxicities varied significantly; all of the evaluated essential oils were less effective than silicone oils and paraffin oil. The LD50 values of the most effective essential oil (blood orange), paraffin oil, and the most effective silicone oil (dodecamethylpentasiloxane) are 0.184 ± 0.018, 0.069 ± 0.012, and 0.036 ± 0.005 mg per bug, respectively. Direct spray of 1% water solution of 3-[hydroxy (polyethyleneoxy) propyl] heptamethyltrisiloxane, the only silicone oil that mixes well with water, resulted in 92% bed bug mortality after 1 d. Results of this study indicate silicone oils and paraffin oil have the potential to be used as safer alternative bed bug control materials.

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Ecotoxicology
Toxicities of Selected Essential Oils, Silicone Oils, and
Paraffin Oil against the Common Bed Bug (Hemiptera:
Cimicidae)
ChenZha1,3, ChangluWang1, and AndrewLi2
1Department of Entomology, Rutgers University, New Brunswick, NJ 08901, 2USDA, ARS, Invasive Insect Biocontrol and Behavior
Laboratory, Beltsville, MD 20705, and 3Corresponding author, e-mail: chen.zha1@rutgers.edu
Subject Editor: Murray Isman
This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or a
recommendation by the USDA for its use. USDA is an equal opportunity provider and employer.
Received 9 May 2017; Editorial decision 18 September 2017
Abstract
The common bed bug [Cimex lectularius L. (Hemiptera: Cimicidae)] and tropical bed bug [Cimex hemipterus
F. (Hemiptera: Cimicidae)] resurged in the United States and many other countries over the past decades. The
need for safe and effective bed bug control products propelled the development of numerous ‘green insecticides’,
mostly with essential oils listed as active ingredients. Various inorganic and organic oils also were used for bed
bug management. However, there are no published studies on their toxicities against bed bugs. In this study, we
screened 18 essential oils, three silicone oils, and paraffin oil (C5-20 paraffins) for their toxicities against bed bugs.
All the oils exhibited insecticidal activity in topical assays. Their toxicities varied significantly; all of the evaluated
essential oils were less effective than silicone oils and paraffin oil. The LD50 values of the most effective essential
oil (blood orange), paraffin oil, and the most effective silicone oil (dodecamethylpentasiloxane) are 0.184±0.018,
0.069 ± 0.012, and 0.036 ± 0.005 mg per bug, respectively. Direct spray of 1% water solution of 3-[hydroxy
(polyethyleneoxy) propyl] heptamethyltrisiloxane, the only silicone oil that mixes well with water, resulted in 92%
bed bug mortality after 1 d.Results of this study indicate silicone oils and paraffin oil have the potential to be used
as safer alternative bed bug control materials.
Key words: Cimex lectularius, essential oil, paraffin oil, silicone oil, toxicity
The common bed bug, Cimex lectularius L. (Hemiptera: Cimicidae),
is an obligate blood feeder, which resurged world-wide in recent
decades (Doggett et al. 2004, Davies et al. 2012). Another similar
pest species, the tropical bed bug [Cimex hemipterus F. (Hemiptera:
Cimicidae)], was also recently documented in Florida after being
absent in over six decades (Campbell et al. 2016). Treatment with
insecticides is frequently used by professional pest controllers as well
as residents in an attempt to eliminate bed bug infestations. In a
senior citizen occupied building in Indiana, 40% of the 40 inter-
viewed residents indicated they self-applied insecticides for bed bug
control (Wang et al. 2010), while 89% of 18 interviewed residents
treated bed bugs on their own in another study in New Jersey (Wang
et al. 2014). Professional products such as Temprid SC (21% imi-
dacloprid + 10.5% β-cyuthrin; Bayer Environmental Science,
Research Triangle Park, NC), Suspend SC (4.75% deltamethrin;
Bayer Crop Science, Research Triangle Park, NC), and Demand CS
(9.7% λ-cyhalothrin; Syngenta Crop Protection, Greensboro, NC)
are widely utilized by licensed pesticide applicators in the United
States. In addition to professional insecticide products, the major-
ity of commercially available consumer bed bug control insecticides
on the U.S. market are also pyrethrins or pyrethroids, with a few
exceptions like silica gel and diatomaceous earth dusts (Wang et al.
2014). The effectiveness of pyrethrins and pyrethroids against bed
bugs is sometimes questionable, due to the wide-spread resistance to
pyrethroids among bed bug populations (Romero et al. 2007, Zhu
et al. 2010, Davies et al. 2012). Besides pyrethrins and pyrethroids,
many essential oil-based products, that is, ‘green insecticides’, for
controlling bed bugs have been developed in recent years. The con-
cept of green insecticide refers to all types of natural-oriented pest
control materials (Koul et al. 2008). One of the reasons companies
develop product lines with essential oils as green insecticides is that
many products are exempt from the requirements of the Federal
Insecticide, Fungicide, and Rodenticide Act (FIFRA) under the mini-
mum risk exemption regulations (US EPA 2015); therefore, manu-
facturers do not need to pay expenses for US EPA registration and
they can get their product to market quicker and are exempt from
Journal of Economic Entomology, 111(1), 2018, 170–177
doi: 10.1093/jee/tox285
Advance Access Publication Date: 6 December 2017
Research Article
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EPA regulation. As EPA exempt products, federal registration is not
required, and many of these products are ineffective against bed bugs.
Out of 11 tested essential oil-based insecticides and detergents, only
EcoRaider bed bug killer (1% geraniol + 1% cedarwood oil + 2%
sodium lauryl sulfate; Reneotech, Inc., North Bergen, NJ) and Bed
Bug Patrol (0.003% clove oil + 1% peppermint oil + 1.3% sodium
lauryl sulfate; Nature’s Innovation, Inc., Buford, GA) caused > 90%
mortality to bed bug nymphs when using direct spray evaluation
(Singh et al. 2014). In a eld study, EcoRaider caused similar bed bug
population reduction as Temprid SC and EcoRaider + Temprid SC
mixture spray (Wang et al. 2014). The different efcacies among the
essential oil-based products indicate the necessity for further investi-
gation of the relative toxicity of individual essential oils.
Numerous essential oils are shown to be effective against insect
pests in laboratory and eld assays and used for pest control.
For example, thyme and peppermint are used to control green-
house whiteies [Trialeurodes vaporariorum Westw. (Hemiptera:
Aleyrodidae)] (Aroiee et al. 2005). Eucalyptus oil is effective in
killing or repelling insects such as Culex pipiens L. (Diptera:
Culicidae) (Erler etal. 2006), Tribolium confusum Duv. (Coleoptera:
Tenebrionidae), Ephestia kuehniella Zell. (Lepidoptera: Pyralidae)
(Tunc et al. 2000), and Sitophilus zeamais Motsch. (Coleoptera:
Curculionidae) (Ngamo etal. 2003). Essential oils also have poten-
tial in structural and household pest management. Polyethylene gly-
col–coated nanoparticles loaded with garlic essential oil is effective
against red our beetle [Tribolium castaneum Herbst. (Coleoptera:
Tenebrionidae)] (Yang etal. 2009). Phillips etal. (2010) evaluated the
toxicities of 12 essential oils against German cockroaches [Blattella
germanica L.(Blattodea: Blattellidae)] and found thymol and trans-
cinnamaldehyde to be the most effective. Various terpenoid compo-
nents in essential oils are responsible for the toxicity against insects;
for example, thymol and carvacrol, the two components of thyme
oil showed high insecticidal activity against Alphitobius diaperinus
Panz. (Coleoptera: Tenebrionidae) when applied alone (Szczepanik
etal. 2012). Limonene from citrus extract is effective against mealy-
bugs and scale insects (Hollingsworth 2005). Piperitone and trans-
ethyl cinnamate isolated from the essential oil of Artemisia judaica
L.showed pronounced insecticidal and antifeedant activity against
Spodoptera littoralis Boisd. (Abdelgaleil et al. 2008). Neem oil is
not, strictly speaking, an essential oil but a xed vegetable oil but
is also included in our screening process since it has been widely
used in pest management. Neem oil has been used for decades to
control pests such as brown planthopper (Nilaparvata lugens Stål
[Hemiptera: Delphacidae]), black bug (Scotinophara lurida Burm.
[Hemiptera: Pentatomidae]), and earhead bug (Leptocorisa acuta
Thunb. [Hemiptera: Alydidae]) (Isman etal. 1990, Schmutterer 1990,
Lokanadhan etal. 2012). Azadirachtin, a complex tetranortri-terpe-
noid limonoid from the neem seeds, is the main component respon-
sible for both antifeedant and toxic effects in insects (Nisbet 2000).
Many silicone oils are chemically stable and safe materials, com-
monly used in many daily necessities and medications that make dir-
ect contact to the human body. Silicone oil can be used in shampoo
(Hössel etal. 2000), skin cream (Sawada and Sone 1990), industrial
fermentation (Ates etal. 2002), and even cooking (Dana and Saguy
2006). Silicone oil is used in coating surfaces of various medical
equipments (e.g., syringes and stoppers) (Jones etal. 2005). Silicone
oil injections are common in vitreous microsurgery (Cox etal. 1986).
Interestingly, silicone oils also have some properties that make
them an excellent candidate for insecticides. These oils are generally
considered as unreactive and safe to humans. Many silicone oils are
light in weight, odorless, and colorless, which make them easy to
apply with little issue of clogging, staining, and smelling. Some sili-
cone oils are water soluble and used as surfactants.
The toxicity of certain silicone oils against insects has been deter-
mined in previous studies. Asilicone oil, Silwet L-77 (Helena Chemical
Co., Collierville, TN), a non-ionic surfactant, has been proven to be
effective against multiple agricultural pests (Imai etal. 1995, Purcell
and Schroeder 1996, Tipping etal. 2003). A few other trisiloxane
surfactants have insecticidal activity against two spotted spider mite
(Cowles et al. 2000). Despite the fact that silicone oils themselves
may have insecticidal activities, they are more often listed as inert
ingredients in insecticide formulations (Knoche 1994). Besides agri-
cultural use, silicone oils have been applied on human ectoparasites
as well. Dimeticone is found to be effective against head lice (Burgess
2009, Heukelbach etal. 2010). Asilicone oil-based commercial prod-
uct, Nopucid Bio Citrus (Laboratorio ELEA, Argentina) that contains
dimethicone, ciclopentaxiloxane, and bergamot essential oil, can
cause 100% mortality in head lice after exposed for 1min (Gallardo
etal. 2012). Therefore, it is plausible that certain silicone oils could be
effective against bed bug, which is also a human ectoparasite.
Parafn oil (C5-20 parafns) is a transparent, colorless, and odor-
less mineral oil. Similar to silicone oil, parafn oil is frequently found in
commonly used products such as lamp oil. Although the toxicity of par-
afn oil against insects is still unknown, the use of other mineral oils in
pest management has been tested in previous research. Sprays of Luxan
Oil H (93% mineral oil) and synthetic insecticides mixtures inhibited
the spread of aphid-born nonpersistently transmitted lily symptom-
less virus and lily mottle virus in Lilium L.(Liliales: Lilieae) (Asjes and
Blom-Barnhoorn 2000). Spray application of a mineral oil, Orchex 796
(Exxon, Houston, TX), provided additional control to codling moth and
secondary pests on apple, although the benet was hard to detect when
the pest density was high (Fernandez etal. 2005). Besides agricultural
use, petroleum-derived mineral oils are also effective against ectopara-
sites such as mites and lice; Wolf etal. (2016) found a mineral oil-based
head lice shampoo to be a safe and effective alternative for insecticide-
based pediculicides. Therefore, there is a potential of using mineral oils
in bed bug control. Among all the different mineral oils, parafn oil was
chosen in our study to evaluate toxicity against bed bugs, because it is a
light oil and will have less likelihood to stain mattresses, furniture, and
other personal belongings compared to heavieroils.
In this study, 18 different essential oils, 3 silicone oils, and par-
afn oil were tested in the laboratory for their toxicities against bed
bugs. Among the essential oils chosen for the study, cedarwood and
palmarosa (geraniol) are active ingredients of EcoRaider; ve dif-
ferent cedarwood oils were included because the species of cedar-
wood for extracting the oil used in EcoRaider is undisclosed by the
manufacturer. The other essential oils are also readily available and
have shown toxicities against insects in previous studies, as listed in
Table1. One silicone oil (dodecamethylpentasiloxane) is listed in
a bed bug control product as inert ingredients (BestYet, Cedarcide
Industries, Inc., Spring, TX), the other silicone oil (cyclopentasilox-
ane) is similar to dodecamethylpentasiloxane in viscosity, and the
last one (3-[hydroxy(polyethyleneoxy)propyl]heptamethyltrisilox-
ane) is listed in a developing formula (Siltech Corporation, Inc.,
Toronto, Ontario, Canada). These silicone oils exhibited high toxici-
ties against bed bugs in our preliminary studies. Our goal is to iden-
tify safe and effective alternative chemicals for controlling bedbugs.
Materials and Methods
Chemicals
In total, 18 essential oils, three silicone oils, and parafn oil were
included in the study (Table1). Essential oils vary considerably in
their composition depending upon where the plants were grown, the
season of harvest, the conditions prevailing during that year, and
even the manufacturer/supplier. The main constituents of oils listed
171
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in Table 1 were based on the Material Safety Data Sheet (MSDS)
provided by the manufacturer. If no MSDS from manufacturer was
available, the main constituents were obtained from related litera-
ture without listing their concentrations. An essential oil-based con-
sumer product, EcoRaider bed bug killer, also was used in this study
to compare against pure essential oils.
Insects
A eld strain of bed bug (Indy) was used in this study. It was collected
from multiple apartments during 2008 through 2009 in a building in
Indiana and was moderately resistant against pyrethroids (Singh et al.
2014). Bed bugs were maintained in plastic containers (5 cm diameter
and 4.7 cm height; Consolidated plastics, Stow, OH) with folded con-
struction paper (40 mm length and 30 mm width; Universal Stationers
Supply Co., Deereld, IL) as harborages and held at 26 ± 1°C, 40
± 10% relative humidity (RH), and a 12:12 (L:D) h photoperiod.
They were fed biweekly on debrinated rabbit blood (Hemostat
Laboratories, Dixon, CA) using a Hemotek membrane-feeding
system (Discovery Workshops, Accrington, United Kingdom). Bed
bugs were fed 1 wk prior to all experiments.
Experiment 1: Initial Screening of 22Oils
In total, 18 essential oils, 3 silicone oils, and parafn oil were screened
for their toxicities through topical assay. All oils were diluted to 0.2g/ml
in acetone. Adult male bed bugs of unknown age were used in this
experiment. Adroplet of 0.5µl liquid was delivered onto each bed bug’s
dorsal thorax by a hand micro-applicator (Burkard Manufacturing
Co. Ltd., Rickmansworth, Hertfordshire, United Kingdom), which
equaled to approximately 0.1-mg oil per bug. Treated bed bugs were
placed in groups of 10 on Fisherbrand P5 lter paper (3.5-cm diam-
eter; Fisher Scientic, Pittsburgh, PA) in a petri dish (5.5-cm diameter
and 1.5-cm height; Fisher Scientic). Each treatment was replicated
four times. Bed bugs in the control group were treated with acetone
with the same number of bugs and replications.
The treated bed bugs were kept in an incubator (Percival
Scientic, Inc., Perry, IA) at 25°C, a 12:12 (L:D) h light cycle, and
Table1. Essential oils, silicone oils, and paraffin oil tested in experiment1
Oil name Source plant Country of
origin
Main constituents and reference Manufacturer and registration
number
Anise star Illicium verum China 82.5% Anethole (Chang and Ahn 2002) New Direction Aromatics Inc.
(Mississauga, Ontario, Canada),
CAS 8007-70-3
Basil Sweet Ocimum basilicum, ct.
Estragole
India 73.06% Methyl chavicol (estragole);
19.2% linalool (Chang etal. 2009)
New Direction Aromatics Inc.,
CAS 8015-73-4
Blood orange Citrus sinensis Italy 98% Limonene (Hollingsworth 2005) New Direction Aromatics Inc.,
CAS 8028-48-6
Cedarwood Atlas Cedrus atlantica Morocco 45.95% b-Himalachene1 New Direction Aromatics Inc.,
CAS 8000-27-9
Cedarwood Chinese Cupressus funebris China 14.75% Thujopsene; 10.19% a-cidrene;
10% cedrol
New Direction Aromatics Inc.,
CAS 8000-27-9
Cedarwood Himalayan Cedrus deodora India 50.04% Himalchene New Direction Aromatics Inc.
CAS 68991-36-6
Cedarwood Texas Juniperus ashei / mexicana United States 34% Thujopsenene; 26% cedrol New Direction Aromatics Inc.,
CAS 68990-83-0
Cedarwood Virginian Juniperus virginiana United States 22.53% Cedrol; 20.31% thujopsenene New Direction Aromatics Inc.,
CAS 8000-27-9
Eucalyptus Blue Mallee Eucalyptus polybractea Australia 87.40% 1,8-Cineole (Lee etal. 2004) New Direction Aromatics Inc.,
CAS 8000-48-4
Eucalyptus Dives Eucalyptus dives Australia 52.07% Piperitone (Abdelgaleil etal.
2008); 20.38% a-phellandrene
New Direction Aromatics Inc.
CAS 90028-48-1
Eucalyptus Lemon Eucalyptus citriadora China 82.1% Citronellal (Koul etal. 2008) New Direction Aromatics Inc.,
CAS 85203-56-1
Neem Azadirachta indica - Azadirachtin (Isman etal. 1990) Lotus Brands, Inc. (Twin Lakes, WI)
Oregano Origanum vulgare Hungary Carvacrol, thymol (Lambert etal. 2001) Puritan’s Pride, Inc. (Oakdale, NY)
Palmarosa Cymbopogon martinii var
motia
India 83.8% Geraniol New Direction Aromatics Inc.,
CAS 8014-19-5
Peppermint Mentha × piperita L. India Menthol, menthone (Edris and Farrag
2003)
Puritan’s Pride, Inc.
Spearmint Mentha spicata China l-Carvone (Koul etal. 2008) New Direction Aromatics Inc.
Tea Tree Melaleuca alternifolia China 41.02% Terpinen-4-ol (Isman 2000) New Direction Aromatics Inc.,
CAS 68647-73-4
Thyme Thymus vulgaris — Thymol, carvacrol (Szczepanik etal.
2012)
Envisage Essentials (Canton, GA)
Silicone oil 1 — — 100% Dodecamethylpentasiloxane Clearco Products Co., Inc.
(Bensalem, PA). CAS 141-63-9
Silicone oil 2 — — 100% Cyclopentasiloxane Clearco Products Co., Inc.
(Bensalem, PA). CAS 541-02-6
Silicone oil 3 — — 90% 3-[Hydroxy(polyethyleneoxy)pro-
pyl] heptamethyltrisiloxane
Gelest, Inc. (Morrisville, PA),
CAS 67674-67-3
Parafn oil — — 100% C5-20 parafns Lamplight Farms Inc. (Menomonee,
WI), CAS 64771-72-8
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were observed at 1, 3, 5, 7, and 14 d post-treatment. The numbers
of dead and moribund bed bugs were recorded at each observation
period. Adead bug was dened as no signs of activity when gently
prodded with a pair of lightweight forceps. Amoribund bug was
dened as bug that still can move its’ appendages, when prodded,
but cannot turn over or walk. Both dead and moribund bugs were
included in mortality during analysis.
After the initial screening, the three silicone oils were tested again
using the same method at a lower dose (0.04mg oil per bug) to deter-
mine if there are signicant differences in toxicities among them.
Experiment 2: Evaluating LD50 of SelectedOils
Three oils (blood orange, parafn oil,and silicone oil 1)were included
in this experiment. Blood orange and silicone oil 1 were the most
effective oils in the respective category based on results of Experiment
1.Adult males and females of mixed ages were used in this experi-
ment. Tested solutions were applied to bed bugs using the same
method as in Experiment 1.Blood orange was diluted to 0.2, 0.3,
0.4, 0.5, and 0.6g/ml and equaled to doses of 0.1, 0.15, 0.2, 0.25,
and 0.3mg oil per bug, respectively. Parafn oil and silicone oil 1 was
diluted to 0.04, 0.08, 0.12, 0.16, and 0.2g/ml and equaled to doses of
0.02, 0.04, 0.06, 0.08, and 0.1mg oil per bug, respectively. Eight bed
bugs of unknown age (four males and four females) were used in each
treatment and each treatment had four replications. Bed bugs in the
control group were treated with acetone. Less number of bed bugs
and both sexes were used compared to other experiments due to the
limited number of adults in the laboratory colony during experiment.
After treatment, the bed bugs were maintained in the same man-
ner as in Experiment 1. The numbers of dead and moribund bed
bugs were recorded at 1, 3, and 14 d post-treatment. Both dead and
moribund bugs were included in mortality during analysis, and mor-
tality at day 3 was used to calculate LD50.
Experiment 3: Comparison of Different Cedarwood
Oils, Geraniol, and EcoRaider by TopicalAssay
This experiment was designed to investigate if the origin and source
of plants affects the efcacy of essential oils and to compare the ef-
cacy of formulated essential oils (EcoRaider) and individual essential
oil components. EcoRaider, ve cedarwood oils, and geraniol were
included in this experiment. The oils represented the two major
active ingredients in EcoRaider: cedarwood oil and geraniol. The
ve cedarwood oils were from different source plants and origins,
and they had different chemical components (Table1); three of the
ve “cedarwood oils” were actually not from Cedrus at all but other
genera of plants and consequently bear no similarity to cedar wood
oil sensu stricto. The type of cedarwood oil used in EcoRaider was
not disclosed by the manufacturer. Adroplet of 0.5-µl EcoRaider
(original product) or essential oils (0.2g/ml in acetone) were applied
onto bed bugs through topical assay, following the same method
described in Experiment 1.Bed bug mortalities were recorded at 1,
3, 5, and 7 d post-treatment. Bed bugs in the control group were
treated with acetone. After treatment, the bed bugs were held in the
same way as in Experiment1.
Experiment 4: Efficacy of Silicone Oil 3 Water
Solution Against Bed Bugs by DirectSpray
Silicone oil 3 was the only tested silicone oil which can be evenly
mixed with water without any surfactant. Bed bugs (10 males and
10 third to fth instar nymphs) were placed in a petri dish (5.5-cm
diameter and 1.5-cm height) lined with lter paper (3.5-cm diameter)
on the bottom and sprayed with 0.1, 0.5, and 1% silicone oil 3 water
solutions. The solutions were applied to insects using a Potter spray
tower (Burkard Scientic Ltd, Herts, United Kingdom) at the rate
of 4.07 mg/cm2 (1 gallon/1,000 ft2). Treated bed bugs were trans-
ferred to clean petri dishes after spray. Each treatment was replicated
three times, and water was used in the control. The bed bugs were
held in the same manner following treatment, as in Experiment 1.
Mortality of bed bugs was observed at 1 d post-treatment.
Statistical Analysis
The efcacies of different oils in Experiment 1 were compared by
Kruskal–Wallis Test because data of some tested groups were not
normally distributed even after transformation. Probit analysis was
applied to calculate LD50 values in Experiment 2. The mortalities
caused by different cedarwood oils and geraniol in Experiment 3
were compared by analysis of variance followed by Tukey’s HSD
Fig.1 Mortality of bed bugs after topically treated with different oils at the dose of 0.1mg oil per bug, arranged in order by mean rank scores. There was no
mortality in the control.
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test, the mortalities at 1 and 7 d after topical assay in each treatment
were compared by paired t-test. All analyses were performed using
SAS software version 9.3 (SAS Institute Inc. 2011).
Results
Toxicities of 22 Oils Against BedBugs
Bed bug mortalities stabilized at 3 d after topical application of
selected oils; therefore, 3-d data were used for comparison. There
were signicant differences in the mean bed bug mortalities
(χ2=62.67; df=21; P<0.001), varying from 5±3% (spearmint)
to 100±0% (dodecamethylpentasiloxane) (Fig. 1). The three sili-
cone oils and the parafn oil had highest mean rank scores among
all the oils, and blood orange had the highest mean rank score
among all essential oils (Table2). There was no mortality in the
control.
At the lower dose of 0.04mg per bug, the silicone oils 1 (dodeca-
methylpentasiloxane), 2 (cyclopentasiloxane), and 3 (3-[hydroxy
(polyethyleneoxy) propyl] heptamethyltrisiloxane) caused 65 ± 3,
25±7, and 33±3% mortality, respectively; the efcacies of the three
silicone oils were statistically different (χ2=8.10; df=2; P=0.017),
with a mean rank score of 10.5 for silicone oil 1, 3.8 for silicone oil
2, and 5.3 for silicone oil 3.There was no mortality in the control.
LD50 of SelectedOils
Because a few bugs that were knocked down at 1 d recovered at
3 d, only mortality data at 3 d were used in LD50 value analysis.
Dead or moribund bugs on day 3 were not recovered after day 14.
The LD50 values of blood orange, parafn oil, and silicone oil 1
were 0.184±0.018, 0.069±0.012, and 0.038±0.005mg per bug,
respectively (Table3). The relative toxicities of these three oils were
silicone oil 1>parafn oil>blood orange. There was no mortality
in the control.
Comparison of Different Cedarwood Oils, Geraniol,
and EcoRaider by TopicalAssay
The mortality at 1 d ranged from 15±8% (geraniol) to 50±14%
(cedarwood Chinese), there were no signicant differences
among the tested cedarwood oils, geraniol, and EcoRaider at 1
d (F= 1.65; df= 6, 21; P=0.182). From 1–7 d, the mortalities
in different essential oil treatments did not change signicantly
(Table4); on the other hand, the mortality in EcoRaider treatment
increased signicantly from 38 ±10% to 93± 5% (t =−4.16;
df= 3; P=0.025; Fig. 2). The mortality in EcoRaider treatment
was signicantly higher than other treatments at 7 d (F=9.38;
df=6, 21; P<0.001; Tukey’s HSD test, P<0.05). There was no
mortality in the control.
Efficacy of Silicone Oil 3 Water Solution Against Bed
Bugs by DirectSpray
Silicone oil 3 solution killed 15±5, 88±2, and 92±5% bed bugs
at the concentration of 0.1, 0.5, and 1% after 1 d in direct spray,
respectively. The mortalities after 7 d were 18±5, 90 ± 0, and
92±5% at the concentration of 0.1, 0.5, and 1%, respectively. There
was no mortality in the control.
Discussion
All the tested oils showed some level of toxicity against bed bugs.
However, the toxicities of different oils varied according to oil type,
origin, and source plants. For example, there are different types of
cedarwood oils. The ve cedarwood oils included in our study were
from four origins, extracted from six different tree species, and had
different main constituents. The insecticidal constituents of many
plant extracts and essential oils are monoterpenoids (Negahban etal.
2007). Therefore, the constituents and concentrations of terpenoids
are more critical than the trade name of the essential oils; the efcacy
of oils with the same name from different sources or manufactur-
ers may vary signicantly, while different oils with similar chemical
constituents could be used as replacement for advantages in cost and
availability. Therefore, it is necessary to understand their differences
and clearly list the source plants and constituents when used for pest
management purposes. Further studies of the effectiveness of iso-
lated terpenoids against bed bug would benet the development of
essential oil-based insecticide products.
Our study revealed parafn oil and the three silicone oils were
ranked higher in toxicity than all the essential oils tested. Besides
higher toxicities, parafn oil and silicone oils have additional
advantages over essential oils as insecticides. Parafn and silicone
oils are generally odorless and colorless, while essential oils usually
have strong odors. Although the odors from essential oil are often
described as fragrant and pleasing, some of them might be unpleas-
ant and even irritating to some people due to personal preference.
Some essential oils, such as blood orange, are colored and may stain-
treated items. Parafn oil and silicone oils hold promise as safe and
effective alternative bed bug control materials.
Table2. Mean rank scores of the toxicities of different oils ranked
by Kruskal–Wallis test
Oils
Mean rank
score Oils Mean rank score
Silicone oil 1 83.0 Tea Tree 40.3
Silicone oil 3 81.0 Eucalyptus Blue
Mallee
36.1
Silicone oil 2 79.0 Cedarwood Texas 35.5
Parafn oil 79.0 Cedarwood Atlas 32.8
Blood orange 66.0 Palmarosa 32.8
Cedarwood Chinese 57.0 Peppermint 27.1
Cedarwood Virginian 51.6 Eucalyptus Dives 26.5
Thyme 51.6 Neem 23.0
Oregano 44.8 Basil Sweet 20.8
Cedarwood Himalayan 43.8 Anise star 15.1
Eucalyptus Lemon 40.6 Spearmint 11.8
Table3. Probit analysis results of the tested oils
Oil nSlope±SE LD50 (95% CI) (mg/bug) χ2P
Blood orange 160 9.71±1.51 0.184 (0.166–0.202) 41.48 <0.001
Parafn oil 160 6.15±1.12 0.069 (0.060–0.081) 30.25 <0.001
Silicone oil 1 160 7.66±1.15 0.038 (0.032–0.043) 44.29 <0.001
174 Journal of Economic Entomology, 2018, Vol. 111, No. 1
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Previous studies suggested that silicone oils kill target insects by
physical means. Richling and Böckeier (2008) tested a dimeticone-
based pediculicide Nyda (G. Pohl-Boskamp GmbH & Co. KG,
Hohenlockstedt, Germany) against head lice [Pediculus humanus
capitis De Geer (Phthiraptera: Pediculidae)] and house crickets
[Acheta domestica (Linnaeus) (Orthoptera: Gryllida)] and con-
cluded that dimeticone was capable of entering the tracheal system,
with subsequent asphyxiation in insects. On the other hand, Burgess
(2009) suggested that a 4% dimeticone/96% cyclomethicone prod-
uct, Hedrin (Thornton & Ross Ltd, Hudderseld, United Kingdom),
killed lice by entering spiracles and tracheae of lice, which would
lead to disruption of water management, subsequent osmotic stress
and gut rupture. Although the mechanism of parafn oil has not
been discussed previously, some other petroleum-derived mineral
oils were thought to have a physical mode of action based on cover-
ing and suffocation of ectoparasites such as mites and lice (Agnello
2002, Taverner 2002, Wolf etal. 2016). The mode of action of sili-
cone and parafn oils against bed bug is probably similar, since
death occurred instantly after treatment, with no prolonged effect
observed. Further examination by microscopic tools such as scan-
ning electron microscope on bugs treated by silicone and parafn
oils may help us understand the modes of action of theseoils.
The different time-mortality patterns of EcoRaider compared
with individual essential oils suggest that by combining different
essential oils or using special formulating techniques, the efcacy of
essential oils can be signicantly increased. In experiment 3, compar-
ing different oils and EcoRaider, the total amount of active ingredi-
ents applied to each insect was much higher in the cedarwood oil and
geraniol treatments (0.2 g/ml in acetone) compared to EcoRaider
(1% geraniol + 1% cedarwood oil). Yet, EcoRaider resulted in much
greater mortality. The additional mortality after 7 d treatment in
the EcoRaider treatment also suggests that formulated essential
oils could have additional insecticidal effect beyond the initial kill
shortly after exposure. Many essential oils are known for their high
volatility (Negahban etal. 2007); terpenoids in oils may evaporate
soon after application, which explains why all essential oils tested in
the study alone did not show additional mortality over time. In the
case of EcoRaider, the additional slow killing effect and high efcacy
are probably a result of the interactions of multiple ingredients and
a special formulating process; one possible mode of action is that
surfactants damage the wax layer of insect cuticle and facilitated
the penetration of terpenoids through cuticle, which remain in the
body and cause prolonged death. Further studies on the interaction
of essential oils, silicone oils, parafn oil, and other inert ingredients
in insecticide formulations are warranted for developing more effect-
ive formulations based on various oils.
Acknowledgments
We thank Qi Zhang for bed bug colony maintenance. We also thank Dr.
Lena Brattsten at department of Entomology, Rutgers for providing us access
to the hand micro-applicator. This study was supported by the National
Institute of Food and Agriculture, U.S. Department of Agriculture Hatch
project 1001098, through the New Jersey Agricultural Experiment Station,
Hatch project NJ08127. This is New Jersey Experiment Station publication
D-08-08127-03-17.
Table4. Changes in mortalities at 1 and 7 d after topical assay in different oil treatments
Oil 1-d mortality% 7-d mortality% Paired t-test
Cedarwood Atlas 20.0±4.1 22.5±4.8 t=−0.52; df=3; P=0.638
Cedarwood Chinese 50.0±14.1 47.5±13.1 t=1.00; df=3; P=0.391
Cedarwood Himalayan 25.0±8.7 30.0±7.1 t=−1.73; df=3; P=0.182
Cedarwood Texas 25.0±11.9 22.5±12.5 t=1.00; df=3; P=0.391
Cedarwood Virginian 30.0±4.1 32.5±6.3 t=−1.00; df=3; P=0.391
Geraniol 15.0±5.0 17.5±6.3 t=−1.00; df=3; P=0.391
EcoRaider* 37.5±10.3 92.5±4.8 t=−4.16; df=3; P=0.025
*Signicant difference (paired t-test, P<0.05).
Fig.2 Mortality of bed bugs treated with different cedarwood oils, geraniol, and EcoRaider at the dose of 0.1mg oil or 0.5µl EcoRaider original solution per bug.
There was no mortality in the control.
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