Evaluation of benzaldehyde derivatives from Morinda officinalis as anti-mite agents with dual function as acaricide and mite indicator

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus with 12-30% fatality rate. Despite severity of the disease, any medication or treatment for SFTS has not developed yet. One approach to prevent SFTS spreading is to control the arthropod vector carrying SFTS virus. We report that 2-methylbenzaldehyde analogues from M. officinalis have a dual function as acaricide against Dermatophagoides spp. and Haemaphysalis longicornis and indicator (color change) against Dermatophagoides spp. Based on the LD50 values, 2,4,5-trimethylbenzaldehyde (0.21, 0.19, and 0.68 μg/cm(3)) had the highest fumigant activity against D. farinae, D. pteronyssinus, and H. longicornis, followed by 2,3-dimethylbenzaldehyde (0.46, 0.44, and 0.79 μg/cm(3)), 2,4-dimethylbenzaldehyde (0.66, 0.59, and 0.95 μg/cm(3)), 2,5-dimethylbenzaldehyde (0.65, 0.68, and 0.88 μg/cm(3)), 2-methylbenzaldehyde (0.95, 0.87, and 1.28 μg/cm(3)), 3-methylbenzaldehyde (0.99, 0.93, and 1.38 μg/cm(3)), 4-methylbenzaldehyde (1.17, 1.15, and 3.67 μg/cm(3)), and M. officinalis oil (7.05, 7.00, and 19.70 μg/cm(3)). Furthermore, color alteration of Dermatophagoides spp. was shown to be induced, from colorless to dark brown, by the treatment of 2,3-dihydroxybenzaldehyde. These finding indicated that 2-methylbenzaldehyde analogues could be developed as functional agent associated with the arthropod vector of SFTS virus and allergen.

Full text

Evaluation of benzaldehyde derivatives
from Morinda officinalis as anti-mite
agents with dual function as acaricide
and mite indicator
Ji-Yeon Yang
1
, Min-Gi Kim
1
, Jun-Hwan Park
1
, Seong-Tshool Hong
2
& Hoi-Seon Lee
1
1
Department of Bioenvironmental Chemistry and Institute of Agricultural Science and Technology, College of Agricultural and Life
Sciences, Chonbuk National University, Jeonju 561–756, Republic of Korea,
2
Department of Biomedical Sciences and Institute of
Medical Science, Chonbuk National University, Chonju, Chonbuk 561–712, Republic of Korea.
Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS
virus with 12–30% fatality rate. Despite severity of the disease, any medication or treatment for SFTS has not
developed yet. One approach to prevent SFTS spreading is to control the arthropod vector carrying SFTS
virus. We report that 2–methylbenzaldehyde analogues from
M. officinalis
have a dual function as acaricide
against
Dermatophagoides
spp. and
Haemaphysalis longicornis
and indicator (color change) against
Dermatophagoides
spp. Based on the LD
50
values, 2,4,5–trimethylbenzaldehyde (0.21, 0.19, and
0.68 mg/cm
3
) had the highest fumigant activity against
D. farinae
,
D. pteronyssinus
, and
H. longicornis
,
followed by 2,3–dimethylbenzaldehyde (0.46, 0.44, and 0.79 mg/cm
3
), 2,4–dimethylbenzaldehyde (0.66,
0.59, and 0.95 mg/cm
3
), 2,5–dimethylbenzaldehyde (0.65, 0.68, and 0.88 mg/cm
3
), 2–methylbenzaldehyde
(0.95, 0.87, and 1.28 mg/cm
3
), 3–methylbenzaldehyde (0.99, 0.93, and 1.38 mg/cm
3
), 4–methylbenzaldehyde
(1.17, 1.15, and 3.67 mg/cm
3
), and
M. officinalis
oil (7.05, 7.00, and 19.70 mg/cm
3
). Furthermore, color
alteration of
Dermatophagoides
spp. was shown to be induced, from colorless to dark brown, by the
treatment of 2,3–dihydroxybenzaldehyde. These finding indicated that 2–methylbenzaldehyde analogues
could be developed as functional agent associated with the arthropod vector of SFTS virus and allergen.
A
ppearance of new infectious diseases creates serious health threat to the world. Ebola and Severe fever with
thrombocytopenia syndrome are the typical example of new infectious diseases, which were recently
discovered in West Africa and Northeast Asia
1
. The SFTS is characterized by fever, leukocytopenia,
respiratory problems, gastrointestinal symptoms, and thrombocytopenia
1
. The etiological agent of SFTS is
SFTS virus, a novel bunyavirus, which is carried by a tick, Haemaphysalis longicornis. Although the prevalence
of SFTS is rare, the disease is a serious disease in which fatality rate range from 12 to 30%
2
. However, there has not
been developed any medication or treatment for SFTS yet. More seriously, the population of H. longicornis is
increasing because of global warming
2
, suggesting that SFTS could threaten the world near future.
House dust mites, such as Dermatophagoides pteronyssinus and Dermatophagoides farinae, play directly as a
strong allergen to cause a number of allergic diseases, of which atopic dermatitis and allergic rhinitis are the most
prevalent diseases
1
. Although changes in housing environments with local heating, repeated ventilation, and
limited use of fitted carpets are a solution to control acari, which are the subclass of ticks and mites, the control of
acari by improvement of house conditions has a definite limitation
3
. Therefore, there is urgent demand for
development of an agent controlling acari effectively to prevent allergic diseases and diseases spread by acari
including SFTS.
Traditional control methods have been performed using many approaches, such as the following: (1) imple-
mentation of exceptional cleaning standards; (2) improvement of habitat of mites and ticks; and (3) use of
synthetic acaricides, such as avermectin, c–benzene hexachloride, chlopyrifos–methyl, DEET, fenitrothion,
pirimiphos–methyl, etc
4–6
. In spite of the outstanding effects of these synthetic acaricides against mites and ticks,
their repeated treatment has resulted in the occurrence of resistance, environmental impact, and side effects in
non–target organisms
7
. For example, Van Leeuwen et al.
8
had reported that avermectin in mites acts on glutam-
ate–gated chloride channels and c-aminobutyric acid (GABA). Resistance of avermectin causes an increase of
OPEN
SUBJECT AREAS:
RISK FACTORS
BIOMEDICAL MATERIALS
Received
9 September 2014
Accepted
3 November 2014
Published
1 December 2014
Correspondence and
requests for materials
should be addressed to
H.-S.L. (hoiseon@jbnu.
ac.kr)
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 1

excretion and decreases of absorption with conjugated compound
8
.
In light of these problems, there is a need for the development of
alternatives for the control of mites and ticks, such as more efficient
and safer chemicals of natural origin
9
.
Plants have been found as prospective alternatives to a number of
chemicals because of the abundance of materials designated as tra-
ditional herbal medicine
10–11
. Morinda officinalis How (family
Rubiaceae), cultivated in subtropical and tropical regions, has been
used in traditional herbal medicines and nutrient supplements for
more than 2,000 years
12–13
. To date, various biological activities of M.
officinalis roots have been reported, including antiosteoporosis
14
,
antifatigue
15
, antioxidant
16
, hypoglycemic
17
, and antidepressant
agents
17
. In addition, various chemicals have been found in M. offi-
cinalis roots, including anthraquinone, carbohydrate, iridoid gluc-
oside, iridoid lactone, rotungenic, and b–sitosterol
17
. These findings
indicated that M. officinalis roots should have important pharmaco-
logical properties
14–18
. In this regard, the potential ability of M. offi-
cinalis roots to act as a natural acaricide against mites and ticks was
assessed in the present study.
Results and Discussion
Essential oil was extracted from M. officinalis roots with a yield of
0.03%. To determine the acaricidal potential, the acaricidal activity of
M. officinalis oil was evaluated using the contact and the fumigant
bioassays against Dermatophagoides spp. and H. longicornis .
Compared with the LD
50
values of DEET, the acaricidal activity of
M. officinalis oil (7.05, 7.00, and 19.70 mg/cm
3
) proved to be more
toxic than that of DEET (36.50, 34.23, and 52.03 mg/cm
3
) against D.
farinae, D. pteronyssinus, and H. longicornis in the fumigant assay,
respectively (Table 1). In case of the contact bioassay, the acaricidal
effect of M. officinalis oil (5.57, 5.00, and 15.48 mg/cm
2
) was also
more potent than that of DEET (19.64, 14.12, and 47.77 mg/cm
2
)
against D. farinae, D. pteronyssinus, and H. longicornis, respectively
(Table 1). The negative treatment, injection of acetone alone, did not
result in the death of dust mites and ticks in the fumigant and the
contact bioassays. The acaricidal potential of M. officinalis oil
depends on the species of mites, chemicals, and biological condi-
tions
19
. Thus, M. officinalis oil has the potential ability as a natural
acaricide against Dermatophagoides spp. and H. longicornis.
The M. officinalis oil was analyzed by GC–MS, and the retention
index, retention time, and mass spectra of each compound were
compared to those reported in the literature
20
. A list of the constitu-
ents from M. officinalis oil is provided in Table 2. The relative
composition (%) of the constituents of M. officinalis oil was 1–
allyl–4–methoxybenzene (2.42%), 1,2–benzenedicarboxylic acid
(4.54%), c–butyrolactone (2.74%), hexadecanoic acid (6.47%),
hexanoic acid (2.42%), 2–methylanthraquinone (8.00%), 2–
methylbenzladehyde (31.97%), 8–methylundecene (2.94%), myristal-
dehyde (6.53%), 1,3,12–nonadecatriene (2.63%), nonanoic acid
(4.27%), 9,17–octadecadienal (2.09%), paeonol (11.26%), and c–stear-
olactone (2.20%). The constituents of M. officinalis oilweregroupedas
acids (1,2–benzedicarboxylic acid, hexadecanoic acid, hexanoic acid,
and nonanoic acid), aldehydes (2–methylbenzaldehyde and myristal-
dehyde), alkenes (8–methylundecene, 1,3,12–nonadecatriene, and
9,17–octadecadienal), benzenes (1–allyl–4–methoxybenzene), lactones
(c–butyrolactone and c–stearolactone), phenols (paeonol), and qui-
nones (2–methylanthraquinone). According to Yong–tao (2009)
21
,the
volatile components of M. officinalis oil were borneol, diisobutyl
phthalate, linoleic acid, 3–methylbenzaldehyde, and oleic acid
22
.In
the present and previous studies, the constituents of M. officinalis
oil were influenced by the environmental conditions, including the
handling method, harvest time, intraspecific variability, storage period,
and the experimental conditions, which included the method of
extraction and the parts of the plant extracted
20
.
To isolate the active constituent of M. officinalis oil, various chro-
matographic analyses were conducted using column chromato-
graphy and liquid chromatography. The MO322 fraction was
finally isolated from M. officinalis oil, and the structure was identified
by spectroscopic analyses including
1
H–NMR,
13
C–NMR, and
DEPT–NMR spectra. The isolated MO322 fraction was character-
ized as 2–methylbenzaldehyde (Figure 1) (C
8
H
8
O); EI–MS (70 eV)
m/z M
1
120.06;
1
H–NMR (CDCl
3
, 400 MHz) d 2.48 (s, 3H), 7.26–
7.44 (d, J 5 7.2 Hz, 1H), 7.45–7.59 (t, J 5 5.6 Hz, 1H), 7.61–7.75 (t, J
5 5.6 Hz, 1H), 7.77–7.90 (d, J 5 5.2 Hz, 1H), and 10.36 (s, 1H);
13
C–
NMR and DEPT–NMR (CDCl
3
, 100 MHz) d 18.6 (CH3), 191.0
(CH), 126.2 (CH), 131.9 (CH), 13.1.9 (CH) 134.4 (C), 134.4 (CH),
139.6 (C). The findings of 2–methylbenzaldehyde were compared
with those of a previous study
23
. The acaricidal activity of 2–methyl-
benzaldehyde isolated from M. officinalis oil was evaluated using the
contact and the fumigant bioassays against Dermatophagoides spp.
and H. longicornis and compared with that of DEET. The LD
50
values
of 2–methylbenzaldehyde in the fumigant bioassay were 0.95, 0.87,
and 1.28 mg/cm
3
against D. farinae, D. pteronyssinus, and H. long-
icornis, respectively (Table 3). In the contact bioassay, the LD
50
values of 2–methylbenzaldehyde were observed to be 0.51, 0.47,
and 0.94 mg/cm
2
against D. farinae, D. pteronyssinus, and H. long-
icornis, respectively (Table 4). In comparison with the LD
50
values of
DEET in the fumigant bioassay, 2–methylbenzaldehyde was
approximately 38.58, 39.30, and 40.58 times more effective than
DEET (36.50, 34.23, and 52.03 mg/cm
3
) against D. farinae, D. pter-
onyssinus, and H. longicornis (Table 3). In the contact bioassay, it was
about 38.48, 30.04, and 50.60 times more toxic than DEET (19.64,
14.12, and 47.77 mg/cm
2
) against D. farinae, D. pteronyssinus, and H.
longicornis (Table 4). In this regard, the acaricidal activity of 2–
methylbenzaldehyde was much more potent than that of DEET, a
Table 1
|
Acaricidal activities of M. officinalis oil and acaricide against Dermatophagoides spp. and H. longicornis
1
Samples Bioassay Species LD
50
6 SE 95% CL RT
2
M. officinalis oil Fumigant (mg/cm
3
) D. farinae 7.05 6 0.11 6.84–7.24 5.18
D. pteronyssinus 7.00 6 0.04 6.87–7.13 4.89
H. longicornis 19.70 6 0.11 19.63–19.77 2.64
Contact (mg/cm
2
) D. farinae 5.57 6 0.04 5.50–5.64 3.53
D. pteronyssinus 5.00 6 0.06 4.95–5.06 2.82
H. longicornis 15.48 6 0.12 15.42–15.55 3.09
DEET Fumigant (mg/cm
3
) D. farinae 36.50 6 0.12 36.44–36.55 1.00
D. pteronyssinus 34.23 6 0.03 34.18–34.29 1.00
H. longicornis 52.03 6 0.07 51.99–52.07 1.00
Contact (mg/cm
2
) D. farinae 19.64 6 0.05 19.63–19.66 1.00
D. pteronyssinus 14.12 6 0.16 14.11–14.13 1.00
H. longicornis 47.77 6 0.04 47.72–47.82 1.00
1
Exposed for 24 h.
2
RT, Relative toxicity 5 LD
50
value of DEET/LD
50
value of each compound.
www.nature.com/scientificreports
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 2

commercial acaricide, against D. farinae, D. pteronyssinus, and H.
longicornis.
To establish the structural relationships between 2–methylbenzal-
dehyde analogues and acaricidal activities against Dermatophagoides
spp. and H. longicornis, 2,3–dihydroxybenzaldehyde, 2,5–dihydrox-
ybenzaldehyde, 2,4–dihydroxybenzaldehyde, 2,3–dimethylbenzal-
dehyde, 2,4–dimethylbenzaldehyde, 2,5–dimethylbenzaldehyde, 2–
hydroxybenzaldehyde, 3–hydroxybenzaldehyde, 4–hydroxybenzal-
dehyde, 3–methylbenzaldehyde, 4–methylbenzaldehyde, 2,4,5–tri-
hydroxybenzaldehyde, and 2,4,5–trimethylbenzaldehyde were
selected as 2–methylbenzaldehyde analogues for testing (Figure 1).
The acaricidal activities of 2–methylbenzaldehyde analogues were
evaluated using the contact and the fumigant bioassays against D.
farinae, D. pteronyssinus, and H. longicornis. In the fumigant bioas-
say (Table 3), the acaricidal activities of 2,4,5–trimethylbenzaldehyde
(0.21, 0.19, and 0.68 mg/cm
3
) were approximately 178.02, 178.30, and
76.07 times more toxic than those of DEET (36.50, 34.23, and
52.03 mg/cm
3
) against D. farinae, D. pteronyssinus, and H. longicor-
nis, followed by 2,3–dimethylbenzaldehyde (0.46, 0.44, and 0.79 mg/
cm
3
), 2,4–dimethylbenzaldehyde (0.66, 0.59, and 0.95 mg/cm
3
), 2,5–
dimethylbenzaldehyde (0.65, 0.68, and 0.88 mg/cm
3
), 2–methylben-
zaldehyde (0.95, 0.87, and 1.28 mg/cm
3
), 3–methylbenzaldehyde
(0.99, 0.93, and 1.38 mg/cm
3
), and 4–methylbenzaldehyde (1.17,
1.15, and 3.67 mg/cm
3
). In the contact bioassay (Table 4), the acar-
icidal effects of 2,4,5–trimethylbenzaldehyde (0.12, 0.19, and
0.46 mg/cm
2
) were about 170.99, 73.53, and 103.61 times more active
than those of DEET (19.64, 14.12, and 47.77 mg/cm
2
) against D.
farinae, D. pteronyssinus, and H. longicornis, followed by 2,3–
dimethylbenzaldehyde (0.25, 0.24, and 0.56 mg/cm
2
), 2,4–dimethyl-
benzaldehyde (0.32, 0.32, and 0.62 mg/cm
2
), 2,5–dimethylbenzalde-
hyde (0.35, 0.36, and 0.74 mg/cm
2
), 2–methylbenzaldehyde (0.51,
0.47, and 0.94 mg/cm
2
), 3–methylbenzaldehyde (0.53, 0.50, and
1.02 mg/cm
2
), and 4–methylbenzaldehyde (0.63, 0.61, and 1.84 mg/
cm
2
). In contrast, 2,3–dihydroxybenzaldehyde, 2,4–dihydroxyben-
zaldehyde, 2,5–dihydroxybenzaldehyde, 2–hydroxybenzaldehyde,
3–hydroxybenzaldehyde, 4–hydroxybenzaldehyde, and 2,4,5–trihy-
droxybenzaldehyde did not show the acaricidal activity against D.
farinae, D. pteronyssinus,orH. longicornis in the contact and the
fumigant bioassays. Comparison of the LD
50
values from the contact
and the fumigant bioassays against D. farinae, D. pteronyssinus, and
H. longicornis revealed that the acaricidal activities of the structural
analogues containing a methyl (CH
3
) functional group (2,3–
dimethylbenzaldehyde, 2,4–dimethylbenzaldehyde, 2,5–dimethyl-
benzaldehyde, 2–methylbenzaldehyde, 3–methylbenzaldehyde, 4–
methylbenzaldehyde, and 2,4,5–trimethylbenzaldehyde) were more
potent than those of structural analogues containing a hydroxyl
(OH) functional group (2,3–dihydroxybenzaldehyde, 2,4–dihydrox-
ybenzaldehyde, 2,5–dihydroxybenzaldehyde, 2–hydroxybenzalde-
hyde, 3–hydroxybenzaldehyde, 4–hydroxybenzaldehyde, 2,4,5–
trihydroxybenzaldehyde). In particular, the number of methyl func-
tional groups influenced the acaricidal activity against D. farinae, D.
pteronyssinus, and H. longicornis. These observations are similar with
the results in the study by Oh et al.
18
in which 29–methylacetophe-
none, 39–methylacetophenone, and 49–methylacetophenone were
Table 2
|
Analysis of various constituents from M. officinalis oil identified by GC–MS
Retention Time Constituents
Retention Index
1
Relative composition (%)DB–5 HP–Innowax
5.56 Hexanoic acid 974 1005 2.42
8.94 2–Methylbenzladehyde 1095 1128 31.97
10.70 Nonanoic acid 1272 1301 4.27
11.13 1–Allyl–4–methoxybenzene 1190 1224 2.42
11.97 8–Methylundecene 1140 1168 2.94
12.27 c–Butyrolactone 1284 1313 2.74
13.48 Paeonol 1439 1472 11.26
16.81 Myristaldehye 1601 1633 6.53
18.81 9,17–Octadecadienal 1997 2035 2.09
19.51 Hexadecanoic acid 1968 1999 6.47
20.90 1,3,12–Nonadecatriene 1916 1948 2.63
21.06 c–Stearolactone 2178 2214 2.20
21.36 2–Methylanthraquinone 2069 2101 8.00
25.00 1,2–Benzenedicarboxylic acid 2248 2284 4.54
1
Retention Intex, Kovats index of retention.
Figure 1
|
Structure–activity relationships of 2–methylbenzaldehyde analogues. (a) 2–Methylbenzaldehyde; (b) 3–Methylbenzaldehyde; (c) 4–
Methylbenzaldehyde; (d) 2–Hydroxybenzaldehyde; (e) 3–Hydroxybenzaldehyde; (f) 4–Hydroxybenzaldehyde; (g) 2,3–Dimethylbenzladehyde; (h) 2,4–
Dimethylbenzladehyde; (i) 2,5–Dimethylbenzladehyde; (j) 2,3–Dihydroxybenzladehyde; (k) 2,4–Dihydroxybenzladehyde; (l) 2,5–
Dihydroxybenzladehyde; (m) 2,4,5–Trimethylbenzladehyde; (n) 2,4,5–Trihydroxybenzladehyde.
www.nature.com/scientificreports
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 3

observed to have potent activities while 29,49–dihydroxyacetophe-
none and 29,69–dihydroxyacetophenone possessed no activities
against D. farinae and D. pteronyssinus. According to Lee and
Lee
22
, the acaricidal effects of 2–methyl–1,4–naphthoquinone, which
has a methyl functional group added onto 1,4–naphthoquinone,
were more toxic against D. farinae and D. pteronyssinus than those
of 2–hydroxy–1,4–naphthoquinone, containing a hydroxyl func-
tional group on 1,4–naphthoquinone.
Color alterations of Dermatophagoides spp. were observed
through an optical microscope when before and after treatment with
M. officinalis oil and 2–methylbenzaldehyde structural analogues. In
particular, Dermatophagoides spp. treated with M. officinalis oil and
2,3–dihydroxybenzaldehyde presented with skin discoloration to a
dark brown color in the body, while the untreated mites were color-
less (Figure 2). The color change of the mites treated with M. offici-
nalis oil and 2,3–dihydroxybenzaldehyde allowed D. farinae and D.
pteronyssinus to be distinguish with the naked eye. According to a
previous study, complete elimination is actually impossible due to
residual mite excrement and dead mites
24
. In addition, a vicious cycle
of the treatments of the commercial acaricides was continued. These
problems have emphasized the demand for the development of new
technologies to control the allergens caused by Dermatophagoides
spp. In this regard, the mite indicator in this study is valuable because
of the color alteration of Dermatophagoides spp. induced by M. offi-
cinalis and 2,3–dihydroxybenzaldehyde. For these reasons, a new
concept for natural acaricides was found in the present study, invol-
ving both the acaricidal activity and the mite indicator against
Dermatophagoides spp. The discoloration is likely to be related to
the benzene ring metabolisms of the defense mode of action in
plants
22,25
. A similar reaction was previously observed in the whole
body of dust mites treated with quinone
22
. Lee and Lee reported that
polyphenol oxidase catalyzed two reactions: hydroxylation and
Table 3
|
Acaricidal activities of 2–methylbenzaldehyde analogues and commercial acaricide against Dermatophagoides spp. and H.
longicornis, using a fumigant bioassay
1
Compounds Species LD
50
6 SE (mg/cm
3
) 95% CL RT
2
2–Methylbenzaldehyde D. farinae 0.95 6 0.04 0.89–1.01 38.58
D. pteronyssinus 0.87 6 0.02 0.84–0.90 39.30
H. longicornis 1.28 6 0.12 1.19–1.38 40.58
3–Methylbenzaldehyde D. farinae 0.99 6 0.06 0.91–1.07 36.86
D. pteronyssinus 0.93 6 0.02 0.90–0.97 36.69
H. longicornis 1.38 6 0.15 1.33–1.43 37.62
4–Methylbenzaldehyde D. farinae 1.17 6 0.07 1.07–1.27 31.19
D. pteronyssinus 1.15 6 0.02 1.12–1.18 29.79
H. longicornis 3.67 6 0.05 3.62–3.71 14.19
2–Hydroxybenzaldehyde D. farinae 1.32 6 0.14 1.12–1.52 27.63
D. pteronyssinus 1.27 6 0.07 1.17–1.37 26.98
H. longicornis 2
3
22
32Hydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
42Hydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
2,3–Dimethylbenzaldehyde D. farinae 0.46 6 0.02 0.45–0.48 78.99
D. pteronyssinus 0.44 6 0.02 0.41–0.47 77.80
H. longicornis 0.79 6 0.15 0.73–0.85 65.78
2,4–Dimethylbenzaldehyde D. farinae 0.66 6 0.08 0.56–0.76 55.30
D. pteronyssinus 0.59 6 0.03 0.55–0.63 58.02
H. longicornis 0.95 6 0.05 0.87–1.02 55.00
2,5–Dimethylbenzaldehyde D. farinae 0.65 6 0.05 0.58–0.71 56.58
D. pteronyssinus 0.68 6 0.10 0.54–0.82 50.34
H. longicornis 0.88 6 0.12 0.83–0.93 58.92
2,3–Dihydroxybenzaldehyde D. farinae 7.53 6 0.30 7.11–7.95 4.85
D. pteronyssinus 6.69 6 0.59 5.87–7.51 5.12
H. longicornis 222
2,4–Dihydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
2,5–Dihydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
2,4,5–Trimethylbenzaldehyde D. farinae 0.21 6 0.02 0.18–0.23 178.02
D. pteronyssinus 0.19 6 0.01 0.18–0.20 178.30
H. longicornis 0.68 6 0.09 0.64–0.73 76.07
2,4,5–Trihydroxybenzladehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
DEET D. farinae 36.50 6 0.12 36.44–36.55 1.00
D. pteronyssinus 34.23 6 0.03 34.18–34.29 1.00
H. longicornis 52.03 6 0.06 51.99–52.07 1.00
1
Exposed for 24 h.
2
RT, Relative toxicity 5 LD
50
value of DEET/LD
50
value of each compound.
3
2, no activity.
www.nature.com/scientificreports
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 4

oxidation in the benzene ring metabolisms
21
. In addition, disease
resistance in both insects and mites occurred due to the existence
of polyphenol oxidase
26
.
In the present study, acaricidal effects of M. officinalis oil and 2–
methylbenzaldehyde structural analogues were found against
Dermatophagoides spp. and H. longicornis. In particular, 2,4,5–tri-
methylbenzaldehyde had potent activity against Dermatophagoides
spp. and H. longicornis. From a point of view, M. officinalis oil and 2–
methylbenzaldehyde are the most promising because of the high
sensitivity against D. farinae, D. pteronyssinus, and H. longicornis.
Interestingly, skin color alteration of Dermatophagoides spp. was
exhibited, changing from colorless to dark brown through the treat-
ment with 2,3–dihydroxybenzaldehyde. In this regard, 2,3–dihy-
droxybenzaldehyde could be very useful to observe and remove the
allergens.
In conclusion, this work showed that 2–methylbenzaldehyde ana-
logues from M. officinalis oil have a dual function as acaricide and
acari indicator, meaning that these compounds could be developed
as acaricidal agents. Especially, we believe that 2,3–dihydroxybenzal-
dehyde have a strong potential as an ideal acaricidal agent to control
Dermatophagoides spp. and H. longicornis which are the vector of
SFTS virus and allergen. In the registration process, considering the
fact that Morinda officinalis is a very cheap plant which can be easily
cultivated, the cost would not be a barrier for the commercial
development of 2–methylbenzaldehyde isolated from Morinda
officinalis.
Methods
Compounds. 2,3–Dihydroxybenzaldehyde (97%, Cat No. 189839), 2,4–
dihydroxybenzaldehyde (98%, Cat No. 168637), 2,5–dihydroxybenzaldehyde (98%,
Cat No. D108200) 2,3–dimethylbenzaldehyde (97%, Cat No. 515353), 2,4–
dimethylbenzaldehyde (90%, Cat No. 151041), 2,5–dimethylbenzaldehyde (99%, Cat
No. 151068), 2–hydroxybenzaldehyde (98%, Cat No. W300403), 3–
hydroxybenzaldehyde (97%, Cat No. H19808), 4–hydroxybenzaldehyde (97%, Cat
No. W398403), 3–methylbenzaldehyde (97%, Cat No. T35505), 4–
Table 4
|
Acaricidal activities of 2–methylbenzaldehyde analogues and commercial acaricide against Dermatophagoides spp. and H.
longicornis, using a contact bioassay
1
Compounds Species LD
50
6 SE (mg/cm
2
) 95% CL RT
2
2–Methylbenzaldehyde D. farinae 0.51 6 0.02 0.48–0.54 38.48
D. pteronyssinus 0.47 6 0.01 0.45–0.49 30.04
H. longicornis 0.94 6 0.12 0.92–0.97 50.60
3–Methylbenzaldehyde D. farinae 0.53 6 0.03 0.49–0.57 37.03
D. pteronyssinus 0.50 6 0.01 0.49–0.52 28.07
H. longicornis 1.02 6 0.14 0.96–1.09 46.69
4–Methylbenzaldehyde D. farinae 0.63 6 0.04 0.58–0.68 31.13
D. pteronyssinus 0.61 6 0.01 0.60–0.62 23.26
H. longicornis 1.84 6 0.06 1.80–1.89 25.90
2–Hydroxybenzaldehyde D. farinae 0.70 6 0.06 0.62–0.78 28.13
D. pteronyssinus 0.71 6 0.08 0.61–0.82 19.80
H. longicornis 2
3
22
3–Hydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
4–Hydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
2,3–Dimethylbenzaldehyde D. farinae 0.25 6 0.01 0.24–0.26 78.03
D. pteronyssinus 0.24 6 0.01 0.22–0.26 59.07
H. longicornis 0.56 6 0.15 0.50–0.63 84.69
2,4–Dimethylbenzaldehyde D. farinae 0.32 6 0.01 0.30–0.34 61.07
D. pteronyssinus 0.32 6 0.01 0.30–0.34 44.26
H. longicornis 0.62 6 0.09 0.57–0.67 76.79
2,5–Dimethylbenzaldehyde D. farinae 0.35 6 0.02 0.31–0.38 56.83
D. pteronyssinus 0.36 6 0.05 0.30–0.43 39.00
H. longicornis 0.74 6 0.05 0.69–0.80 64.22
2,3–Dihydroxybenzaldehyde D. farinae 3.79 6 0.10 3.65–3.93 5.19
D. pteronyssinus 3.45 6 0.09 3.33–3.57 4.09
H. longicornis 222
2,4–Dihydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
2,5–Dihydroxybenzaldehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
2,4,5–Trimethylbenzaldehyde D. farinae 0.12 6 0.01 0.10–0.13 170.99
D. pteronyssinus 0.19 6 0.02 0.18–0.20 73.53
H. longicornis 0.46 6 0.07 0.43–0.50 103.61
2,4,5–Trihydroxybenzladehyde D. farinae 222
D. pteronyssinus 222
H. longicornis 222
DEET D. farinae
19.64 6 0.05 19.63–19.66 1.00
D. pteronyssinus 14.12 6 0.16 14.11–14.13 1.00
H. longicornis 47.77 6 0.04 47.72–47.82 1.00
1
Exposed for 24 h.
2
RT, Relative toxicity 5 LD
50
value of DEET/LD
50
value of each compound.
3
2, no activity.
www.nature.com/scientificreports
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 5

methylbenzaldehyde (97%, Cat No. T35602), 2,4,5–trihydroxybenzaldehyde (99%,
Cat No. 526452), and 2,4,5–trimethylbenzaldehyde (99%, Cat No. 493864) were
provided from Aldrich (St. Louis, MO, USA). DEET (95%, Cat No. 32570) was
obtained from Fluka (Buchs, Switzerland).
Essential oil from M. officinalis. Dried roots of M. officinalis (4 kg) were obtained
from a market (Jeonju city, Republic of Korea) and extracted using the steam
distillation extraction method
27
. The essential oil (1.2 g, yield 0.03%) of M. officinalis
roots was concentrated by an evaporator (model name: NAJ–100, EYELA, Tokyo,
Japan) at 27uC and stored at 4uC to prevent loss of the volatile constituents.
Gas chromatography–mass spectrometer. The volatile components of M. officinalis
oil were analyzed by GC–MS (6890 and 5973 series, Agilent, USA) and were separated
using DB–5 and HP–Innowax capillary columns (0.25 mm i.d. 3 3,000 cm L. 3
0.25 mm thickness)
7
. The initial temperature of the GC column was 50u C, which was
gradually increased up to 210uC. The ion source temperature was 230uC. Helium gas
as the carrier gas was flowed at a rate of 0.85 mL/min
7
. Effluents from GC column
were introduced into the mass spectrometer. Mass spectra (m/z) were obtained in
electron ionization (70 eV) set to scan a range of 50–600 amu for 2 seconds. The
volatile components of M. officinalis oil were identified by retention index, retention
time, and mass spectra, and were confirmed by comparison to the published mass
spectra data
28
. The relative composition (%) of volatile components was calculated by
the standard of the internal amount.
Isolation and identification. Silica gel (70–230 mesh) was purchased from Merck
(Rahway, NJ, USA). M. officinalis oil (12 g) was loaded onto a silica gel column (8 cm
i.d. 3 70 cm L.) and eluted gradually using a mixed organic solvent (hexane:ethyl
acetate, gradient, v/v). The eluted fractions were separated by thin–layer
chromatography and a UV lamp (at 264 nm) to obtain eight fractions (MO1–MO8).
The acaricidal activities of the eight fractions were evaluated using the fumigant
bioassay against Dermatophagoides spp. and H. longicornis at a concentration of
59.0 mg/cm
3
. Fraction MO3 fraction (1.98 g, yield 16.5%) was found to possess potent
activity against Dermatophagoides spp. and H. longicornis, and was chromatographed
on a silica gel column using a mixed organic solvent (ethyl aceta te5hexane 5 159, v/v)
to further separa te into five fractions (MO31–MO35). Fraction MO32 (887 mg, yield
44.8%) was identified as the toxic fraction. Next, preparative high performance liquid
chromatography (model name: LC–908, JAI Co., Ltd, Tokyo, Japan) was performed.
Fraction MO32 was separated into three fractions (MO321–MO323) using a GS
column (model name: GS 310, 2 cm i.d. 3 50 cm L.) with methanol solvent as the
mobile phase at a flow rate of 4.8 mL/min. Finally, the active compound (MO322,
130 mg, yield 14.7%) was isolated. The structure of the compound in MO322 fraction
was identified by spectroscopic analyses.
The chemical structure of MO322 fraction isolated from M. officinalis oil was
determined using nuclear magnetic resonance (NMR). To confirm the number of
carbons (C) and protons (H),
13
C–,
1
H–, and DEPT–NMR (model name: JNM–
ECA600 spectrometer, JEOL Ltd., Tokyo, Japan) were implemented at 400 and
100 MHz. The MO322 was melted in CDCl
3
, and tetramethylsilane was used as the
internal standard. In addition, the molecular weight of the MO322 fraction was
investigated using EI–MS (model name: JEOL GSX 400 mass spectrometer, JEOL
Ltd., Tokyo, Japan) spectra.
Target. The rearing method of D. farinae and D. pteronyssinus modified by Yang and
Lee was utilized
3
. The mites were reared without exposure to any synthetic acaricides.
The feed consisted of fry powder and dried yeast (Korea special feed meal Co. Ltd.,
Jeonju, Republic of Korea) given in a rearing case (15 3 12 3 6 cm) at 25uC and 75%
relative humidity (RH) in a dark area. The protein content of the fry powder was
maintained above 49%. For experiments, the Dermatophagoides spp. mites were
placed in a petri dish (9 cm i.d. 3 1.5 cm L.). H. longicornis ticks were collected
around Jeonju River and were identified morphologically and genetically. However,
the H. longicornis ticks were not maintained in our laboratory.
Acaricidal activity. The acaricidal effects of the oil, 2–methylbenzaldehyde, and its
analogues were evaluated using the contact and the fumigant bioassays against
Dermatophagoides spp. and H. longicornis through the method modified by Yang and
Lee
5
. The experimental concentrations in the study were set to scan a range of 60.0–
0.10 mg/cm
2
. Each sample was dissolved in 50 mL acetone and then applied to filter
paper (5.5 cm i.d. 3 25 mm thickness, Whatman, UK). Acetone alone was applied as
the negative control, and DEET was designated as the positive control. The residual
solvent of each filter paper was dried under the fume hood for 14 min. In the contact
bioassay, each piece was placed on the bottom of a petri dish (6 cm i.d. 3 1.5 cm L.).
In the case of the fumigant bioassay, a piece of filter paper was put in the lid of a petri
dish (6 cm i.d. 3 1.5 cm L.) and a thin cotton fabric was inserted to prevent contact of
the inoculated mites with the applied filter paper. Each twenty experimental mites
(Dermatophagoides spp. and H. longicornis), which included a mixture of males and
females, were inoculated in each petri dish, and the lids were sealed. All treatments
were repeated four times and incubated for 24 h at 25uC in the dark. Mortality was
measured by the number of dead ticks and mites, which did not move when prodded
with a pin, under an optical microscope (203, Olympus, Japan).
Color alteration of mites. Color alterations to D. farinae and D. pteronyssinus
exposed to 2–methylbenzaldehyde analogues were evaluated using a light microscope
(1003), as described by Lee et al
25
. Color alteration of the mites before and after
treatment was compared.
Statistics. Mortalities in all the treatments were measured under an optical
microscope (203, Olympus, Japan). D. farinae and D. pteronyssinus were regarded to
be dead when they did not move when touched with a pin. The LD
50
values were
determined by probit analysis
29
. Relative toxicity (RT) was calculated by the ratio of
the commercial acaricide LD
50
value to the LD
50
value observed for each compound.
1. Li, S. et al. Sporadic case infected by severe fever with thrombocytopenia
syndrome bunyavirus in a non–epidemic region of China. Biosci. Trends. 5,
273–276 (2011).
2. Yu, X. J. et al. Fever with thrombocytopenia associated with a novel bunyavirus in
China. N. Engl. J. Med. 364, 1523–1532 (2011).
3. Yang, J. Y. & Lee, H. S. Acaricidal activities of the active component of Lycopus
lucidus oil and its derivatives against house dust and stored food mites
(Arachnida: Acari). Pest Manag. Sci. 68, 567–572 (2012).
4. Stara, J., Stejskal, V., Nesvorna, M., Plachy, J. & Hubert, J. Efficacy of selected
pesticides against synanthropic mites under laboratory assay. Pest Manag. Sci. 67,
446–457 (2011).
5. Yang, J. Y. & Lee, H. S. Changes in acaricidal potency by introducing functional
radicals and an acaricidal constituent isolated from Schizonepeta tenuifolia.
J. Agric. Food Chem. 61, 11511–11516 (2013).
6. Fernandez-Caldas, E., Puerta, L. & Caraballo, L. Mites and allergy. Chem.
Immunol. Allergy. 100, 234–242 (2014).
7. Macchioni, F. et al. Acaricidal activity of pine essential oils and their main
components against Tyrophagus putrescentiae, a stored food mite. J. Agric. Food
Chem. 50, 4586–4588 (2002).
8. Van Leeuwen, T., Vontas, J., Tsagkarakou, A., Dermauw, W. & Tirry, L. Acaricide
resistance mechanisms in the two–spotted spider mite Tetranychus urticae and
other important Acari: A review. Insect Biochem. Mol. Biol. 40, 563–572 (2010).
Figure 2
|
Mite indicators against
D. farinae
and
D. pteronyssinus
. (a) untreated mites, (b) mites, treated with 2,3–dihydroxybenzaldehyde.
www.nature.com/scientificreports
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 6

9. Yang, J. Y. et al. Constituents of volatile compounds derived from Melaleuca
alternifolia leaf oil and acaricidal toxicities against house dust mites. J. Korean Soc.
Appl. Biol. Chem. 56, 91–94 (2013).
10. Lee, H. S. Tyrosinase inhibitors of Pulsatilla cernua root–derived materials.
J. Agric. Food Chem. 50, 1400–1403 (2002).
11. Yang, Y. C. et al. A piperidine amide extracted from Piper longum L. fruits shows
activity against Aedes aegypti mosquito larvae. J. Agric. Food Chem. 50, 3765–3767
(2002).
12. Yang, Z. et al. Isolation of inulin–type oligosaccharides from Chinese traditional
medicine: Morinda officinalis How and their characterization using ESI–MS/MS.
J. Sep. Sci. 33, 120–125 (2010).
13. Yang, Y. J., Shu, H. Y. & Min, Z. D. Anthraquinones isolated from Morinda
officinalis and Damnacanthus indicus. Acta Pharm. Sinica. 27, 358–364 (1992).
14. Wu, Y. B. et al. Antiosteoporotic activity of anthraquinones from Morinda
officinalis on osteoblasts and osteoclasts. Molecules. 14, 573–583 (2009).
15. Zhang, H. L. et al. Structural characterization and anti–fatigue activity
polysaccharides from the roots of Morinda officinalis. Int. J. Biol. Macromol. 44 ,
257–261 (2009).
16. Soon, Y. Y. & Tan, B. K. H. Evaluation of the hypoglycemic and antioxidant
activities of Morinda officinalis in streptozotocin–induced diabetic rats. Singap.
Med. J. 43, 77–85 (2002).
17. Zhang, Z. Q., Yuan, L., Yang, M., Luo, Z. P. & Zhao, Y. M. The effect of Morinda
officinalis How, a Chinese traditional medicinal plant, on the DRL 72–s schedule
in rats and the forced swimming test in mice. Pharmacol. Biochem. Be. 72, 39–43
(2002).
18. Yoshikawa, M., Yamaguchi, S., Nishisaka, H., Yanahara, J. & Murakami, N.
Chemical how: Structures of morindolida and morofficinaloside. Chem. Pharm.
Bull. 43, 1462–1465 (1995).
19. Oh, M. S., Yang, J. Y. & Lee, H. S. Acaricidal toxicity of 29–hydroxy– 49–
methylacetophenone isolated from Angelica koreana roots and structure–activity
relationships of its derivatives. J. Agric. Food Chem. 60, 3606–3611 (2012).
20. Hendriks, M. M. W. B., Juarez, L. C., Bont, D. D. & Hall, R. D. Preprocessing and
exploratory analysis of chromatographic profiles of plant extracts. Anal. Chim.
Acta. 545, 53–64 (2005).
21. Yong–tao, Y. I. Study on extraction of volatile components from Morinda
officinalis How by different methods. J. Anhui Agri. Sci. 24, 85 (2009).
22. Lee, C. H. & Lee, H. S. Color alternation and acaricidal activity of juglone isolated
from Caesalpinia sappan heartwoods against Dermatophagoides spp. J. Microbiol.
Biotechnol. 16, 1591–1596 (2006).
23. Khan, N. H. et al. Easily recyclable polymeric salen complex for the
enantioselective O–acetyl cyanation of aldehyde. J. Mol. Catal. A– Chem. 264,
140–145 (2007).
24. Hong, C. S. House dust mite and clinic allergy. J. Kor. Soc. Allergol. 11, 297–308
(1991).
25. Lee, C. H., Kim, H. W. & Lee, H. S. Acaricidal properties of piperazine and its
derivatives against house–dust and stored food–mites. Pest Manag. Sci. 65,
704–710 (2009).
26. Dilek, T. & Aziz, E. Phenolic compounds in pear juice from different cultivars.
Food Chem. 93, 89–93 (2005).
27. Boutekedjiret, C., Bentahar, F., Belabbes, R. & Bessiere, J. M. Extraction of
rosemary essential oil by steam distillation and hydrodi stillation. Flavour Frag. J.
18, 481–484 (2003).
28. Sadtler Research Laboratories. The Sadtler Standard Gas Chromatography
Retention Index Library (Sadtler Research Laboratories, USA, 1984).
29. Song, H. Y., Yang, J. Y., Suh, J. W. & Lee, H. S. Acaricidal activities of apiol and its
derivatives from Petroselinum sativum seeds against Dermatophagoides
pteronyssinus, Dermatophagoides farinae, and Tyrophagus putrescentiae. J. Agric.
Food Chem. 59, 7759–7764 (2011).
Acknowledgments
This research was supported by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future
Planning (2013R1A2A2A01067945).
Author contributions
J.-Y.Y. designed and carried out the experiments, prepared most of the data, and wrote the
paper; M.-G.K. designed and carried out the experiments, prepared most of the data, and
wrote the paper; J.-H.P. carried out the experiments for the bioassay and assisted in paper–
writing; S.-T.H. wrote the paper; H.-S.L. proposed the key idea of this paper, designed the
experiments, carried out color alteration by introduction of functional radicals, managed
the research process, and wrote the paper.
Additional information
Competing financial interests: The authors declare no competing financial interests.
How to cite this article: Yang, J.-Y., Kim, M.-G., Park, J.-H., Hong, S.-T. & Lee, H.-S.
Evaluation of benzaldehyde derivatives from Morin da officinalis as anti-mite agents with
dual function as acaricide and mite indicator. Sci. Rep. 4, 7149; DOI:10.1038/srep07149
(2014).
This work is licensed under a Creative Commons Attribution-NonCommercial-
NoDerivs 4.0 International License. The images or other third party material in
this article are included in the article’s Creative Commons license, unless indicated
otherwise in the credit line; if the material is not included under the Creative
Commons license, users will need to obtain permission from the license holder
in order to reproduce the material. To view a copy of this license, visit http://
creativecommons.org/licenses/by-nc-nd/4.0/
www.nature.com/scientificreports
SCIENTIFIC REPORTS | 4 : 7149 | DOI: 10.1038/srep07149 7