Novel hydroxy- and epoxy-cis-jasmone and dihydrojasmone derivatives affect the foraging activity of the peach potato aphid myzus persicae (Sulzer) (Homoptera: Aphididae)

Article abstract of DOI:10.3390/molecules23092362

Jasmonates show great potential in sustainable agriculture due to their various roles in natural mechanisms of plant defense, and because they are non-toxic, non-mutagenic, and easily metabolized. The aim of the study was to explore structure-activity relationships of dihydrojasmone, cis-jasmone, and their derivatives at the plant-aphid interface. We focused on the behavioral responses of aphids, following the exogenous application of natural jasmonates and their derivatives to the host plants. Aphid probing behavior was examined using an electrical penetration graph technique (EPG). The chemoenzymatic transformation of cis-jasmone and the activity of two new derivatives are described. The application of cis-jasmone, dihydrojasmone, the hydroxyderivatives, epoxyderivatives, and alkyl-substituted δ-lactones hindered the foraging activity of Myzus persicae (Sulz.) (Hemiptera: Aphididae) during early stages of probing at the level of non-phloem tissues. The application of saturated bicyclic epoxy-δ-lactone enhanced plant acceptance by M. persicae. Jasmonate derivatives containing a hydroxy group, especially in correlation with a lactone ring, were more active than natural compounds and other derivatives studied. Jasmonates of the present study are worth considering as elements of sustainable aphid control as components of the “push-pull” strategy.

Full text of DOI:10.3390/molecules23092362

molecules
Article
Novel Hydroxy- and Epoxy-cis-Jasmone and
Dihydrojasmone Derivatives Affect the Foraging
Activity of the Peach Potato Aphid Myzus persicae
(Sulzer) (Homoptera: Aphididae)
1,
Marlena Paprocka 1, Anna Gliszczyn´ska 2, Katarzyna Dancewicz 1 and Beata Gabrys´
*
1
Department of Botany and Ecology, University of Zielona Góra, Szafrana 1, 65-516 Zielona Góra, Poland;
m.paprocka90@wp.pl (M.P.); k.dancewicz@wnb.uz.zgora.pl (K.D.)
Department of Chemistry, Wrocław University of Environmental and Life Sciences, Norwida 25,
50-375 Wrocław, Poland; anna.gliszczynska@wp.pl
2
*
Correspondence: b.gabrys@wnb.uz.zgora.pl; Tel.: +48-68-328-7317
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 13 July 2018; Accepted: 11 September 2018; Published: 15 September 2018
Abstract: Jasmonates show great potential in sustainable agriculture due to their various roles in
natural mechanisms of plant defense, and because they are non-toxic, non-mutagenic, and easily
metabolized. The aim of the study was to explore structure–activity relationships of dihydrojasmone,
cis-jasmone, and their derivatives at the plant–aphid interface. We focused on the behavioral responses
of aphids, following the exogenous application of natural jasmonates and their derivatives to the
host plants. Aphid probing behavior was examined using an electrical penetration graph technique
(EPG). The chemoenzymatic transformation of cis-jasmone and the activity of two new derivatives are
described. The application of cis-jasmone, dihydrojasmone, the hydroxyderivatives, epoxyderivatives,
and alkyl-substituted
Aphididae) during early stages of probing at the level of non-phloem tissues. The application of
saturated bicyclic epoxy- -lactone enhanced plant acceptance by M. persicae. Jasmonate derivatives
δ-lactones hindered the foraging activity of Myzus persicae (Sulz.) (Hemiptera:
δ
containing a hydroxy group, especially in correlation with a lactone ring, were more active than
natural compounds and other derivatives studied. Jasmonates of the present study are worth
considering as elements of sustainable aphid control as components of the “push–pull” strategy.
Keywords: aphid probing behavior; antifeedant; structure-activity relationships
1. Introduction
Jasmonates form a family of compounds that are synthesized in plants via the octadecanoid
pathway [1]. The first and the main compound in the group of jasmonates biosynthesized in this
pathway is jasmonic acid (JA), which in turn serves as a basic structure for other compounds, such as
methyl jasmonate, cis-jasmone, and jasmonic acid amino acid conjugates that are synthesized in a
living cell [2–4]. The naturally occurring jasmonates participate in plant developmental processes as
phytohormones, are involved in interactions of plants with other organisms, and are vital signaling
molecules in plant responses to various abiotic and biotic stresses, including stresses caused by insect
feeding [5–8].
The Food and Agriculture Organization (FAO) estimates that between 20 and 40 percent of
global crop yields are reduced each year due to the damage caused by plant pests and diseases (http:
//www.fao.org). Arthropods destroy approximately 18–26% of annual crop production worldwide,
at a value of more than $470 billion [9]. The greater proportion of losses (13–16%) occurs in the field,
before harvest, and losses are the heaviest in developing countries. Pre-harvest crop loss caused by
Molecules 2018, 23, 2362; doi:10.3390/molecules23092362
www.mdpi.com/journal/molecules

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aphids may reach over 50% in maize Zea mays L. and 80% in wheat Triticum aestivum L. (Poaceae),
and 80% in Brassica sp. (Brassicaceae) [ ]. Aphids (Hemiptera: Sternorrhyncha: Aphididae) damage
9
crops directly by removing nutrients from sieve elements and act as very efficient vectors of plant
diseases. A study in Australia [10] demonstrated that feeding injury caused by Rhopalosiphum padi L.
and R. maidis (Fitch) was damaging in terms of yield reduction (25.5%) and that Barley yellow dwarf
virus transmitted by R. padi + Sitobion miscanthi (Takahashi) was more damaging than direct feeding,
causing a yield reduction of 39% and an economic loss of $21/ha for wheat. In total, feeding and
virus injuries in cereals, oilseed, and pulse crops resulted in potential economic costs of $241 and
$482 million/year, respectively [10].
At present, direct control of insects in general and aphids in particular depends mainly on the
use of neurotoxic insecticides. Due to the repeated applications, many aphid species, especially the
peach potato aphid Myzus persicae (Sulzer), have developed a resistance to several aphicides [11].
It is expected that the availability and usage of conventional insecticides will be reduced due to their
broad-spectrum toxicity [12] and the employment of environmentally friendly control practices will
provide many benefits, including the economic ones. It is estimated that the return per dollar invested
in ecologically-based biological and cultural pest controls ranges from $30 to $300, significantly higher
than the $4 estimated for control based on synthetic pesticides [9]. Alternative control strategies
are then required and these might include various aspects of plant signaling and volatile secondary
metabolites [13]. The recognition of the crucial role of jasmonates in plant defense systems has
stimulated the exploration of possibilities of practical application of these compounds in insect
control for plant protection. It appeared that the exogenous application of jasmonates could affect
plant metabolism to increase its potential for protection against herbivores, including those with
a piercing-sucking feeding apparatus. Wheat seedlings exposed to methyl jasmonate had higher
concentrations of benzoxazinoid hydroxamic acids and activity of trypsin inhibitors, which deterred R.
padi settling and reduced the total duration of phloem sap ingestion [14]. Wheat seedlings sprayed
with formulated cis-jasmone were less susceptible to attack by grain aphid Sitobion avenae (Fabricius)
than control plants both in the laboratory and in the field [15]. Jasmonic acid application enhanced
wheat yield by causing a reduction in the number of aphids, thrips, and wheat blossom midges [16].
Plant activators, such as cis-jasmone, have the potential to be adopted as a strategy to enhance a
plant’s defense against herbivorous insects, as cis-jasmone elicits aphid-induced stress signaling in
potatoes; the emission of defense volatile organic compounds (VOCs) from potatoes increases after
cis-jasmone treatment, and plants treated with cis-jasmone are repellent to alate Macrosiphum euphorbiae
(Thomas) [17]. cis-Jasmone treatment induced the production of defensive VOCs in field beans Vicia
faba L. (Fabaceae), which attracted beneficial aphid parasitoids, Aphidius ervi Haliday (Hymenoptera:
Aphidiidae) [18]. Similar effect of cis-jasmone application was achieved in wheat plants [19] in
Arabidopsis thaliana L. (Brassicaceae) [20], in cotton Gossypium hirsutum L. (Malvaceae) [21], and in
potato Solanum tuberosum L. (Solanaceae).
Jasmonates show great potential not only due to their various roles in natural mechanisms of
plant defense and the projected practical uses but also because they are non-toxic, non-mutagenic,
and easily metabolized [22]. The issues of environmental and human health effects are becoming
increasingly important in the process of introducing new pesticides [23]. The use of targeted chemicals
that would repel aphids or deter their probing and feeding, thus also limiting virus spread, seems a
promising approach. In the course of our previous studies on aphid antifeedants, we discovered that
certain modifications of the original molecule of the natural compound might lead to compounds with
stronger activities or with activities of quite opposite qualities. Piperitone showed weak attractant
properties and
piperitone/damascone-derived saturated and unsaturated lactones and hydroxy lactones had negative
effects on the probing, feeding, and settling behavior of M. persicae [24 27]. A phenyl substituent at
C-2 in the chromone skeleton and the introduction of an amino group at C-7 of flavone increased the
aphid antifeedant activity [28]. The moderately active -damascone ester affected aphid activities only
β-damascone was behaviorally inactive, but all the derived halogenolactones, and all
–
β

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during phloem phase, while the highly active deterrents—dihydro-
β-damascol,
δ
-bromo-
γ
-lactone,
and unsaturated γ-lactone—affected pre-phloem and phloem aphid probing activities [29]. We found
also that the deterrent activity of decalactones against aphids depended on the size of the lactone ring
and the enantiomeric purity of the compounds [30].
In our most recent studies [31,32] using various fungal strains for biotransformations, we obtained
several hydroxy- and epoxy- derivatives and alkyl-substituted lactones based on the natural structures
of the jasmonate group, in particular, cis-jasmone and dihydrojasmone. Using a simple choice test
to examine their activity against the peach potato aphid, we found that the hydroxyderivative of
dihydrojasmone was an aphid settling deterrent while the original compound was not, and the
hydroxyderivative of cis-jasmone was more active than the starting compound [31]. These observations
were in accordance with the results reported for hydroxyderivatives of another natural compound,
β-damascone [33]. Also, in comparison to dihydrojasmone, the unsaturated lactone showed
weak deterrent properties, the hydroxylactone was a weak attractant, and the saturated bicyclic
epoxy-lactone was a strong attractant [32].
The aim of the present study was to explore in detail the structure–activity relationships of
dihydrojasmone, cis-jasmone, and their derivatives at the plant–aphid interface. We focused on the
behavioral responses of aphids, following the exogenous application of natural jasmonates and their
derivatives to the host plants. Two new compounds and their synthesis using microbial transformations
of cis-jasmone are described. These compounds complement the set of cis-jasmone and dihydrojasmone
derivatives documented in the previously published works [31,32].
2. Results and Discussion
2.1. Chemical Synthesis
The racemic (
±
)-7,8-epoxyjasmone (
5
) was obtained as a product of the Baeyer–Villiger reaction
of cis-jasmone ( ) with m-CPBA (Scheme 1). The structure of the obtained product (
1
5
) was confirmed
by its spectral (IR, 1H, 13C, COSY, and HSQC NMR) data. The absorption band at 1698 cm in the IR
spectrum and the signal form carbonyl carbon atom C-1 with a chemical shift at 209.16 ppm indicated
the presence of an untouched carbonyl group in this molecule. The presence of the oxiran ring in
−1
the structure of product (
the 1H NMR spectrum, respectively. The evidence for its occurrence in the product (
also by 13C NMR, where the signals of C-7 and C-8 were moved from
= 132.35 and
cis-jasmone ( ) to = 55.72 and 58.66 for the product ( ), which was the result of its connection with an
oxygen atom.
5
) was proved by two signals at 2.85 and 3.03 from protons H-8 and H-7 in
) was provided
= 125.09 for
5
δ
δ
1
δ
5
Scheme 1. cis-Jasmone (1) and its derivatives studied towards M. persicae: (+)-(R)-4-hydroxyjasmone
(3), 7,8-epoxyjasmone (5), and 4-hydroxy-7,8-epoxyjasmone (6).
In the next step of the chemoenzymatic modifications of the structure of cis-jasmone (1),
we focused on the evaluation of the usefulness of wild fungal strains in obtaining the oxyderivatives
of ( )-7,8-epoxyjasmone ( ). Nine fungal strains were tested for their ability to transform the substrate
). Two of them, Absidia cylindrospora AM336 and Cunninghamella japonica AM472, transformed
epoxyjasmone ( ) into the more polar metabolite (Scheme 1). No formation of any biotransformation
±
5
(5
5
6

Molecules 2018, 23, 2362
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products of (
±
)-
5
in the cultures of another seven microorganisms was observed even after 8 days
of incubation. 4-Hydroxy-7,8-epoxyjasmone (
7,8-epoxyjasmone ( ). The structure of this hydroxyderivative was determined by its spectral data.
In the 13C NMR spectrum of 4-hydroxy-7,8-epoxyjasmone (
), the chemical shift of carbon atom C-4
6) was the biotransformation product of racemic
5
6
from 34.27 ppm in the structure of substrate to the lower field in the spectrum of product 71.64 ppm
indicated the presence of an oxygen atom in this molecule. This fact was fully confirmed by a signal at
4.77 ppm from proton H-4 observed in the 1H NMR spectrum. The untouched structure of the oxiran
ring was confirmed by two multiplets at
δ = 2.87 and 3.05 from protons H-8 and H-7, respectively.
Additionally, the characteristic absorption band of hydroxyl group (3428 cm−1) in the IR spectrum of
6
was also observed. The product of biotransformation, the 4-hydroxy-7,8-epoxyjasmone (
6), was a new
compound that has not been published before.
The most effective strain able to catalyze the conversion of epoxyjasmone (
hydroxyderivative was Absidia cylindrospora AM336. However, in the first day, the process of
hydroxylation proceeded quite slowly and only 17% of product was observed in the reaction mixture,
and after two days of incubation of substrate with culture A. cylindrospora AM336, the conversion
reached 96%. In the following days, the reaction was continued until the substrate was fully consumed
on the fourth day. The preparative biotransformation of ( )- (100 mg) in the shaken culture of A.
5
) into the
6
6
5
±
5
cylindrospora AM336 after 4 days gave 27 mg (25% isolated yield) of 4-hydroxy-7,8-epoxyjasmone (6)
as a single dextrarotatory isomer (99%de).
Conversion of (
4-hydroxy-7,8-epoxyjasmone (
of incubation.
±
)-7,8-epoxyjasmone (
5
) by means of Cunninghamella japonica AM472 afforded
6) in a low 4% yield but in a pure form of enantiomer ( ) after 4 days
−
The dihydrojasmone (
2) and its derivatives (4, 7, 8, 9, 10) were obtained in the course of the earlier
studies [31,32] and are presented in Scheme 2.
Scheme 2. Dihydrojasmone (
hydroxydihydrojasmone ( ), 3,4-dihydro-5-methyl-6-pentyl-2H-pyran-2-one (
13-dioxabicyclo[4.1.0]hepan-2-one ( ), (-)-5-hydroxy-5-methyl-6-pentyltetrahydro-2H-pyran-2-one (
2
) and its derivatives studied towards Myzus persicae: (+)-(R)-4-
), 5-methyl-6-pentyl-1,
),
4
7
8
9
and 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-ol (10).
2.2. Aphid Behavioral Studies
2.2.1. Aphid Settling
In the present work, we determined the settling success of the peach potato aphid after the
application of the newly obtained cis-jasmone derivatives. The settling preferences of aphids depended
on the compound and the time after the exposure of plants to the compound applied. Aphids avoided

Molecules 2018, 23, 2362
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plants treated with cis-jasmone (
effect ceased by the 24th hour of the experiment. There was also a tendency in aphids to avoid
leaves treated with 4-hydroxy-7,8-epoxyjasmone ( ) but the trend was not significant (Figure 1).
1
) and (
±
)-7,8-epoxyjasmone (
5
) 2 h after exposure, but the deterrent
6
The inconstancy over time in the deterrent effect of various substances has been reported in our earlier
studies, e.g., in the case of piperitone and its derivatives, and the likely explanation was that the
compounds might have been degraded in the plant, translocated to other plant parts via phloem
vessels, or otherwise affected by metabolic processes in the plant or the aphid [25].
0.35
0.30
*
0.25
*
0.20
0.15
0.10
0.05
0.00
(1)
(5)
(6)
1 h 2 h 24 h
Figure 1. Settling success of Myzus persicae on Brassica rapa subsp. pekinensis. exposed to cis-jasmone (1),
7,8-epoxyjasmone (5), and hydroxy-7,8-epoxyjasmone (6). The same plant species was used to maintain
the aphid stock culture. Relative index of deterrence (DI) after 1, 2, and 24 h. ‘*’Asterisks indicate
statistically significant differences between the numbers of aphids on control and treated leaves at
p < 0.05 (one-way ANOVA).
2.2.2. Aphid Behavior during Probing in Plant Tissues
The 8-h Electrical Penetration Graph (EPG) recording revealed various activities related to stylet
penetration in plant tissues: “np”, non-probing, when aphid stylets were withdrawn from the plant,
pathway phase “C”, when aphid stylets were inside peripheral plant tissues, epidermis and mesophyll,
and phloem phase “E”, when aphid stylets were in sieve elements. Sporadically, the “F’” and “G”
waveform patterns occurred indicating unidentified (“derailed”) stylet movements within plant cell
walls and xylem sap uptake, respectively. Due to their rare occurrence irrespective of a treatment,
the periods of “F” and “G” were included in pathway phase “C” in all calculations. Phloem phase
“E” was represented by watery salivation and sap ingestion visualized as “E1” and “E2” waveform
patterns, respectively.
The typical behavior of M. persicae on the control (C) untreated plants consisted predominantly
of active probing (93% of the experimental time), which comprised mainly of activities associated
with phloem phase (60% of the probing time; phloem phase index = 0.6) (Table 1). Probing was rarely
interrupted, and when it was, the non-probing intervals were relatively short: the typical probe was
1.2 h long and the typical “np” interval was 5.8 min long. The first probe was usually more than four
hours long. The sieve elements were reached two hours after the onset of probing and the first period
of sustained sap ingestion occurred within one hour from the first contact with the phloem. Nearly all
aphids reached sieve elements and nearly all of them showed long (ca.
≤
3-h) periods of sustained
waveform E2, indicating successful feeding on treated plants. The contribution of watery salivation to
the phloem phase was 10% (phloem salivation index = 0.1) (Tables 1 and 2, Figure 2). The proportion
of phloem phase increased gradually over the course of time to reach 70% of all aphid activities at the
end of the experiment (Figure 3).

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Table 1. Probing behavior (EPG parameters) of Myzus persicae on Brassica rapa subsp. pekinensis leaves treated with cis-jasmone (
1) and its derivatives:
(+)-(R)-4-hydroxyjasmone (3), 7,8-epoxyjasmone (5), and 4-hydroxy-7,8-epoxyjasmone (6) A. The same plant species was used to maintain the aphid stock culture.
EPG Parameter/Compound
C
1
3
5
6
General Aspects of Aphid Probing Behavior
n = 17
0.6 ± 0.3
2.9 ± 0.5
4.5 ± 0.6
0.6 ± 0.1
6.4 ± 2.0
70.8 ± 13.9
5.8 ± 1.5
n = 16
n = 12
n = 14
1.5 ± 0.6 *
3.0 ± 0.4
3.5 ± 0.6
0.5 ± 0.1
19.9 ± 3.9 *
19.6 ± 3.3 *
4.7 ± 2.0
n = 22
Total duration of np a (h)
Total duration of pathway (h)
Total duration of phloem phase (h)
Phloem phase index b
3.1 ± 0.6 *
2.8 ± 0.7 *
1.2 ± 0.3 *,†
3.2 ± 0.4
2.7 ± 0.3
3.6 ± 0.6
2.2 ± 0.5 *
0.4 ± 0.1 *
21.4 ± 3.0 *
13.2 ± 2.4 *
7.2 ± 1.8
1.7 ± 0.6 *
0.3 ± 0.1 *
34.3 ± 7.0 *
9.1 ± 1.7 *
4.6 ± 1.4 *,†
3.5 ± 0.5
0.5 ± 0.1 †
22.0 ± 4.1 *
18.4 ± 2.8 *
3.4 ± 0.5 †
Number of probes
Mean duration of a probe (min)
Mean duration of np intervals c
Activities in Non-Phloem Tissues before the First Phloem Phase
n = 17
n = 16
n = 12
n = 14
4.7 ± 0.8 *
29.9 ± 16.5 *
1.6 ± 0.5
n = 22
Number of probes
Duration of first probe (min)
2.1 ± 1.0
249.1 ± 54.5
2.0 ± 0.5
2.8 ± 0.6
8.8 ± 2.6 *
10.6 ± 5.1 *
3.5 ± 0.7
4.6 ± 0.6 *
20.1 ± 5.0 *
8.1 ± 4.0 *
4.0 ± 0.9
4.8 ± 0.9
10.5 ± 2.5 *
10.3 ± 4.9 *
2.1 ± 0.4
Time from first probe to first phloem phase(h)
Time from first probe to first sustained sap
ingestion phase E2 > 10 min (h)
Total duration of np (min) c
2.5 ± 0.5 †
3.1 ± 0.7
8.5 ± 3.6
107.5 ± 40.6 *
101.4 ± 46.3 *
36.5 ± 27.7
26.3 ± 8.5 *
Mean duration of np intervals (min)c
4.0 ± 1.6
11.0 ± 3.6
6.6 ± 4.9
2.5 ± 0.5
4.8 ± 1.7 *,†
Activities in Sieve Elements B
149.8 ± 33.0 †
n = 21
160.2 ± 47.6
n = 16
60.8 ± 31.9
n = 12
57.8 ± 44.7
n = 8
100.7 ± 41.4
n = 13
Duration of first phloem phase (min)
156.5 ± 33.7 †
159.7 ± 47.6
n = 16
63.3 ± 31.4
n = 12
92.2 ± 51.6
n = 8
110.5 ± 43.7
n = 12
Duration of first sap ingestion phase (min)
Mean duration of sap ingestion (min)
n = 20
175.8 ± 44.9
n = 16
81.0 ± 30.0
n = 12
101.0 ± 50.3
n = 8
107.9 ± 39.7
n = 12
162.7 ± 31.7
n = 20
0.1 ± 0.0
0.04 ± 0.01
0.1 ± 0.0 *
0.1 ± 0.1
0.1 ± 0.1
Phloem salivation index d
n = 16
n = 12
n = 8
n = 13
n = 21
A
Values are means
±
SE; n = number of replications; *,†—significant differrence in relation to control ( ), respectively (p < 0.05, Mann–Whitney U test); B only aphids
C) and cis-jasmone (1
that showed a phloem phase were used for analysis; a np = non-probing; b E1 + E2/C + E1 + E2 + G + F; c excluding the first non-probing period; d E1/E1 + E2.

Molecules 2018, 23, 2362
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Table 2. Probing behaviour (EPG parameters) of Myzus persicae on Brassica rapa subsp. pekinensis leaves treated with dihydrojasmone (
derivatives: (+)-(R)-4-hydroxydihydrojasmone ( ), 3,4-dihydro-5-methyl-6-pentyl-2H-pyran-2-one ( ), 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-one (
), and 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-ol (10)A. The same plant species was used to
2) and its
4
7
8),
(-)-5-hydroxy-5-methyl-6-pentyltetrahydro-2H-pyran-2-one (
9
maintain the aphid stock culture.
EPG Parameter/Compound
C
2
4
7
8
9
10
General aspects of aphid probing behaviour
n = 17
0.6 ± 0.3
2.9 ± 0.5
4.5 ± 0.6
0.6 ± 0.1
6.4 ± 2.0
70.8 ± 13.9
5.8 ± 1.5
n = 15
n = 14
1.5 ± 0.4 *
3.9 ± 0.7 †
2.7 ± 0.8
n = 14
1.6 ± 0.4 *
2.8 ± 0.5
3.7 ± 0.6
0.6 ± 0.1
16.5 ± 3.3 *
23.3 ± 4.4 *
4.6 ± 1.4
n = 15
n = 11
2.0 ± 0.8 *
3.5 ± 0.7
n = 18
1.3 ± 0.5 *
2.8 ± 0.5
Total duration of np a (h)
Total duration of pathway (h)
Total duration of phloem phase (h)
Phloem phase index b
2.6 ± 0.8 *
1.6 ± 0.4 *
3.4 ± 0.4 †
3.0 ± 0.6
1.8 ± 0.4
3.6 ± 0.7
2.4 ± 0.9
3.9 ± 0.7
0.5 ± 0.1
0.4 ± 0.1
0.4 ± 0.1
0.3 ± 0.1
0.5 ± 0.1
23.4 ± 4.2 *,†
16.7 ± 3.1 *,†
3.9 ± 0.8
28.0 ± 6.2 *,†
13.7 ± 2.3 *,†
3.1 ± 0.8 *,†
26.0 ± 5.2 *,†
13.8 ± 2.8 *,†
3.7 ± 1.6 *,†
Number of probes
12.3 ± 2.8 *
26.5 ± 5.7 *
13.2 ± 4.7
19.1 ± 3.6 *
20.9 ± 3.9 *,†
3.7 ± 1.0
Mean duration of a probe (min)
Mean duration of np intervals c
Activities in non-phloem tissues before 1st phloem phase
n = 17
2.1 ± 1.0
249.1 ± 54.5
2.0 ± 0.5
2.8 ± 0.6
8.5 ± 3.6
4.0 ± 1.6
n = 15
7.1 ± 2.5 *
37.4 ± 25.9 *
2.9 ± 0.8
n = 14
n = 14
7.2 ± 1.6 *
8.3 ± 5.7 *
1.6 ± 0.3
2.7 ± 0.6
17.5 ± 4.9 *
2.4 ± 0.4
n = 15
n = 11
n = 18
Number of probes
Duration of first probe (min)
Time from first probe to first phloem phase(h)
14.7 ± 3.4 *
34.6 ± 30.0 *
3.6 ± 0.8
6.5 ± 1.5 *
16.9 ± 8.2 *
1.4 ± 0.2
14.0 ± 4.6 *
5.6 ± 2.7 *
3.2 ± 1.0
10.3 ± 2.6 *
66.7 ± 36.1 *
2.6 ± 0.6
Time from first probe to first sustained sap ingestion phase E2> 10 min (h)
3.3 ± 0.8
3.8 ± 1.0
2.4 ± 0.5
5.0 ± 1.0
3.0 ± 0.7
Total duration of np (min) c
119.1
±
49.6 *
69.2 ± 27.7 *
4.8 ± 1.2
13.2 ± 6.0
2.0 ± 0.7 *,†
56.0 ± 36.4 *
4.0 ± 2.6 *,†
44.2 ± 24.0 *
4.3 ± 1.8 *,†
Mean duration of np intervals (min) c
16.7 ± 6.8
Activities in sieve elements A
160.2 ± 47.6
n = 16
124.4 ± 49.5
n = 11
131.0 ± 53.0
n = 11
160.5 ± 42.8
n = 14
38.7 ± 17.1
n = 15
80.3 ± 53.1
n = 8
211.6 ± 50.0
n = 16
Duration of first phloem phase (min)
159.7 ± 47.6
n = 16
161.2 ± 53.3
n = 11
132.8 ± 58.5
n = 10
170.6 ± 44.7
n = 13
60.0 ± 24.8
n = 15
108.4 ± 58.2
n = 7
211.4 ± 49.8
n = 16
Duration of first sap ingestion phase (min)
Mean duration of sap ingestion (min)
175.8 ± 44.9
n = 16
167.6 ± 45.0
n = 11
151.5 ± 55.7
n = 10
164.3 ± 45.3
n = 13
68.2 ± 22.3 *
135.8 ± 56.4
n = 7
224.7 ± 47.2
n = 16
n = 15
0.1 ± 0.0 †
n = 15
0.1 ± 0.0
0.01 ± 0.00
0.2 ± 0.1
0.1 ± 0.1
0.2 ± 0.1
0.03 ± 0.01
Phloem salivation index d
n = 16
n = 11
n = 11
n = 14
n = 8
n = 17
A
Values are means
±
SE; n = number of replications; *,†—significant difference in relation to control ( ), respectively (p < 0.05, Mann–Whitney U test); B only
C) and dihydrojasmone (2
aphids that showed a phloem phase were used for analysis; a np = non-probing; b E1 + E2/C + E1 + E2 + G + F; c excluding the first non-probing period; d E1/E1 + E.

Molecules 2018, 23, 2362
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100
90
80
70
60
50
40
30
20
10
0
C
1
3
5
6
2
4
7
8
9
10
cis-jasmone and derivatives dihydrojasmone and derivatives
proportion of aphids with phloem phase
proportion of aphids with sustained sap ingestion phase
Figure 2. Feeding success of Myzus persicae on Brassica rapa subsp. pekinensis exposed to cis-jasmone (
dihydrojasmone ( ) and derivatives: (+)-(R)-4-hydroxyjasmone ( ), (+)-(R)-4-hydroxydihydrojasmone(
7,8-epoxyjasmone ( ), 4-hydroxy-7,8-epoxyjasmone (
), 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-one (
-2H-pyran-2-one ( ), and 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]heptan-2-ol (10). The same plant
1),
2
3
4),
5
6), 3,4-dihydro-5-methyl-6-pentyl-2H-pyran-2- one
(7
8), (-)-5-hydroxy-5-methyl-6-pentyltetrahydro
9
species was used to maintain the aphid stock culture.
Figure 3. Sequential changes in Myzus persicae probing activity on Brassica rapa subsp. pekinensis exposed
to cis-jasmone (
(active deterrent as found in aphid settling assay by Gliszczyn´ska et al. [31]) and 5-methyl-6-pentyl-1,
13-dioxabicyclo[4.1.0]hepan-2-one ( ) (active attractant as found in aphid settling assay by Gliszczyn´ska
1), dihydrojasmone (2), and the most active derivatives: (+)-(R)-4-hydroxyjasmone (3)
8
et al. [32]). E: phloem phase (E1+E2), C: pathway phase (C+F+G), np: non-probing. The same plant
species was used to maintain the aphid stock culture.

Molecules 2018, 23, 2362
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The present study revealed that cis-jasmone (1), dihydrojasmone (
2), and basically all derivatives
of these natural compounds ( and 9–10) affected the course of the pre-ingestive phase of M. persicae
3–
7
probing: the first probe was significantly several times shorter than on the control plants, the probes
were more numerous and separated by 2–16 min non-probing intervals, which resulted in significantly
longer time when aphid stylets were outside of the plant (Tables 1 and 2). The extended time of
non-probing during the pre-phleom phase caused a trend toward the delayed commencement of
feeding in sieve elements on jasmonate-treated plants. Although the significant delay was found only
after the application of cis-jasmone (1), the application of the remaining jasmonates caused a failure
in finding sieve elements in 20–30% of aphids during the 8-h experiment (Tables 1 and 2). It is very
likely that the proportion of aphids that failed to locate phloem would have been higher if the aphids
were not tethered, which was unavoidable in the EPG experiment. Aphid reluctance to probe beyond
outer layers of mesophyll may contribute to the limitation of the transmission of semi-persistent
and persistent viruses [34,35]. As the aphids were visibly restless (made relatively short probes with
relatively long non-probing intervals), they would have left the plants if they were allowed to move.
Indeed, the free-moving aphids showed a tendency to avoid the jasmonate-treated leaves in the
simple choice-assays [31,32] (present study). Nevertheless, when the aphids did reach sieve elements,
they started sap ingestion: sap consumption periods were relatively long and the contribution of watery
salivation to the phloem phase was low and comparable to the control (Tables 1 and 2). This means
that no deterrent factors were detected by the aphids at the phloem level. Similar findings were
reported by Cao et al. [36] who found that on methyl jasmonate-treated wheat plants, the duration of
the first probe by the grain aphid Sitobion avenae was significantly shorter, the number of probes was
significantly higher than those on control plants, and the total duration of probing was significantly
shorter than on control plants. The authors suggested that the methyl jasmonate-dependent resistance
factors might be due to feeding deterrents in mesophyll [36]. Indeed, the ethanolic solution of
cis-jasmone applied to common buckwheat Fagopyrum esculentum (Polygonaceae) seedlings stimulated
the anthocyanins accumulation [37]. cis-Jasmone induced changes in the defense VOCs of cotton and
the VOCs from cis-jasmone-treated plants were significantly repellent to the cotton aphid Aphis gossypii
Glover [21]. It is very likely that the exogenous foliar application of jasmonates in the present study
put in motion plant defense mechanisms at the mesophyll level, probably the synthesis of xenobiotics,
which caused the untimely termination of aphid probing. However, a plant physiology-oriented
study would be necessary to reveal the phenomena beyond the reported aphid behavioral responses.
The application of 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-one (8) had a different final
effect on aphid behavior than the remaining jasmonates in the present study. Although the probes
preceding the first phloem phase were relatively numerous and rather short in comparison to the
control, the non-probing intervals were shorter than on the control, which resulted in the shorter
time to reach phloem vessels than on the control. All aphids on (8)-treated leaves found sieve
elements and started feeding, and sap consumption remained their main activity until the end of the
experiment. The results of the EPG experiment (present study) and the settling assay [32] suggest that
the application of 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-one (8) caused the attraction of
aphids to the (8)-treated leaves.
In a living cell, jasmonates undergo various modifications, such as conjugation with amino acids,
glucosylation, hydroxylation, carboxylation, sulfation, and methylation, which give compounds with
different biological activities. Decarboxylation of JA leads to cis-jasmone, which is less active than JA,
but nevertheless participates in multitrophic interactions involving plants, aphids, and aphid natural
enemies, hydroxylation of JA leads to less active compounds, and conjugation with amino-acids
and lactonization increases the JA biological activity [
compounds cis-jasmone ( ) and dihydrojasmone ( ) was compared to the activity of hydroxyderivatives
(+)-(R)-4-hydroxyjasmone ( ) and (+)-(R)-4-hydroxydihydrojasmone ( ), epoxyderivatives ( )-7,8-
epoxyjasmone (5) and 4-hydroxy-7,8-epoxyjasmone (6), and alkyl-substituted δ-lactones 3,4-dihydro-
5-methyl-6-pentyl-2H-pyran-2-one ( ), 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]heptan-2-one ( ),
8]. In the present study, the activity of natural
1
2
3
4
±
7
8

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5-hydroxy-5-methyl-6-pentyltetrahydro-2H-pyran-2-one (
9
), and 5-methyl-6-pentyl-1,13-dioxabicyclo
[4.1.0]heptan-2-ol (10) by comparing aphid behavior on leaves treated with the derivatives to aphid
behavior on cis-jasmone- and dihydrojasmone-treated leaves (Tables 1 and 2). The activities of
hydroxyderivatives were generally similar to those of the natural compounds, with the exception of
the duration of non-probing intervals, which were shorter on (
) -treated leaves and the frequency and duration of probes, which were more numerous and shorter
on ( )- treated leaves than on dihydrojasmone ( )-treated leaves. The reduction in the duration of
individual non-probing periods on leaves treated with ( ) did not affect the total time that aphids
spent on non-probing activities in comparison to the situation on ( )-treated leaves. The increase in the
number of relatively short probes on ( )-treated leaves caused an increase in the total duration of the
pathway phase activity and a slight decrease in phloem phase activities in comparison to ( )-treated
leaves. The activity of the epoxyderivative ( ) did not differ from the activity of cis-jasmone ( ), but the
application of 4-hydroxy-7,8-epoxyjasmone ( ) caused a decrease in the duration of non-probing
intervals and an increase in the duration of sap ingestion periods in comparison to the values of these
parameters on cis-jasmone ( )-treated leaves. In consequence, the total non-probing time was twice
as short as on cis-jasmone ( )-treated leaves and the phloem phase index was significantly higher on
4-hydroxy-7,8-epoxyjasmone ( )-treated leaves than on cis-jasmone ( )-treated leaves. The activities of
alkyl-substituted -lactones that were obtained from dihydrojasmone ( ) varied, depending on the
compound. The effects of the application of 3,4-dihydro-5-methyl-6-pentyl-2H-pyran-2-one ( ) on
aphid behavior were similar to those caused by dihydrojasmone ( ). The application of 5-methyl-6-
pentyl-1,13-dioxabicyclo[4.1.0]hepan-2-one ( ) and (-)-5-hydroxy-5-methyl-6-pentyltetrahydro-2H-
pyran-2-one ( ) caused a significant reduction in the duration of individual non-probing intervals,
but this did not affect the total time that aphids spent on non-probing activities in comparison to
the effect of the dihydrojasmone ( ) application. At the same time, the probes were more numerous
and shorter on ( )- and ( )-treated leaves than on ( )-treated leaves, which resulted in an increase in
the total duration of pathway activities and the decrease in the phloem phase index. Also, aphids
on ( )-treated leaves were more successful in finding sieve elements and feeding than the aphids on
)-treated leaves. The application of 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]heptan-2-ol (10) caused
3)-treated leaves than on cis-jasmone
(1
4
2
3
1
4
2
5
1
6
1
1
6
1
δ
2
7
2
8
9
2
8
9
2
8
(2
only slight changes in aphid behavior as compared to the dihydrojasmone (2) treatment, with no
significant effect on the overall behavior of aphids (Tables 1 and 2).
All jasmonates that were the subject of the present study are worth considering as elements of
sustainable aphid control, possibly as components of the “push–pull” strategy. In this approach
to insect control, pests are repelled or deterred from the crop (the “push”) and simultaneously
attracted (the “pull”) to other areas, such as trap crops or barrier crops, which act as “sinks” for
non-persistent viruses (viruses are lost by infective vectors while probing on plants of barrier crops)
or mechanical obstacles that impede the colonization of the protected crop [38
to probe beyond outer layers of mesophyll may contribute to the limitation of the transmission
of semi-persistent and persistent viruses [34 35]. Considering the results of the present study,
5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]heptan-2-one ( ), an attractant that enhances the process of
,39]. The reluctance
,
8
plant acceptance by M. persicae, may be used as a “pull” component, while all the remaining substances,
the deterrents that impede the ability of the peach potato aphid to recognize the host plant during the
early stages of probing, may be applied as a “push” component.
3. Material and Methods
3.1. Compounds
The structures of compounds
M. persicae are presented in Schemes 1 and 2. cis-Jasmone (
from Sigma Aldrich (Sigma Aldrich, St. Louis, MI, USA) (cis-jasmone W319600 Sigma Aldrich),
dihydrojasmone W376302 Sigma Aldrich). The hydroxyderivatives and were obtained in the
1–
10 applied for the probing and feeding behavior experiments on
1
) and dihydrojasmone ( ) were purchased
2
3
4

Molecules 2018, 23, 2362
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process of microbial transformation of cis-jasmone (
1
) and dihydrojasmone (
2
), respectively, which
was the content of the paper reported before [31]. Epoxyjasmone (
5) and alkyl-substituted δ-lactones
(7
) and ( ) were synthesized in the reaction with m-chloroperoxybenzoic acid and were subsequently
8
converted into oxyderivatives 6, 9, and 10 using the enzymatic system of wild fungal strains [32].
3.1.1. Microorganisms
In the process of transformation of racemic 7,8-epoxyjasmone (5), nine wild fungal strains
(Fusarium coulmorum AM10, Fusarium equiseti AM15, Botrytis cinerea AM235, Absidia glauca AM254,
Bauveria bassiana AM278, Absidia cylindrospora AM336, Cunninghamella japonica AM472, Chaetomium sp.
KCh6651, and Didymosphaeria igniaria KCh6670) that came from the Department of Chemistry, Wroclaw
University of Environmental and Life Sciences (Wroclaw, Poland) were tested as biocatalysts. The aim
of using the wild type of fungal strains in the process of biotransformation was the economy aspect
of the performed experiments and processes, the results of which can potentially be applied in the
◦
industry. Microorganisms were maintained on Sabouraud 4% dextrose-agar slopes at 4 C and freshly
subcultured before use in the transformation experiments.
All screening experiments, as well as the biotransformations of ( )-7,8-epoxyjasmone (5) in the
±
preparative scale, were carried out according to the method described earlier [31]. A portion of 1 mL of
the pre-incubation culture solution was used to inoculate two or three 2000 mL flasks, each containing
◦
500 mL of the cultivation medium. The cultures were inoculated at 25 C for 48–72 h on a rotary shaker
(150 rpm). Then, 50 mg of a substrate was dissolved in 5 mL of acetone added to each flask. After
1–6 days (depending on the culture) of incubation, the mixtures were extracted with dichloromethane
(3
×
300 mL), dried (MgSO4) and concentrated in vacuo. The transformation products were separated
using column chromatography [32].
3.1.2. Analysis
Gas chromatography (GC) analysis was carried out using a HP-5 column (cross-linked methyl
silicone gum, 30 m
×
0.32 mm
×
0.25 µm) and an FID detector using the following temperature
program: injector 250 ◦C, detector (FID) 250 ◦C, column temperature: 70 ◦C, 70–175 ◦C (rate
◦
◦
◦
◦
20 C/min), 175–300 C (rate 40 C/min), 300 C (hold 2 min). The enantiomeric compositions
of the obtained products were determined using chiral GC analysis with a CP-cyclodextrin-B
◦
(25 m
×
0.25 mm
×
0.25
µ
m) chiral column. The temperature program was as follows: 80 C,
80–200 ◦C (rate 0.6◦/min), 200 ◦C (hold 1 min). NMR spectroscopic measurements were carried out
for CDCl3 solutions on a Bruker Avance AMX 300 spectrometer (Bruker, Rheinstetten, Germany).
IR spectra were performed for liquid films with Thermo-Nicolet IR300 spectrophotometer. Optical
rotations were measured on JASCO P-2000-Na digital polarimeter (JASCO Inc., Easton, MD, USA)
with iRM controller using dichloromethane as a solvent (concentration denoted in g/100 mL).
( )-7,8-Epoxyjasmone (5 δ: 1.04 (t, J = 7.5 Hz, 3H, CH3-10), 1.61 (m,
): oily liquid, 1H NMR (CDCl3),
±
2H, CH2-9), 2.26 (s, 3H, CH3-11), 2.27 (dd, J = 14.3 and 7.3Hz, 1H, one of CH2-6), 2.39 (m, 2H, CH2-4),
2.51-2.54 (m, 3H, CH2-5 and one of CH2-6), 2.85 (m, 1H, H-8), 3.03 (m, 1H, H-7); 13C NMR (CDCl3),
δ
: 209.16 (C-1), 172.55 (C-3), 136.85 (C-2), 58.66 (C-8), 55.72 (C-7), 34.27 (C-4), 31.89 (C-5), 22.09 (C-6),
21.24 (C-9), 17.59 (C-11), 10.64 (C-10); IR (film, cm−1): 1698 (s), 1648 (s), 1385 (m).
4-Hydroxy-7,8-epoxyjasmone (6): oily liquid, 1H NMR (CDCl3),
: 1.06 (t, J = 7.5 Hz, 3H, CH3-10), 1.63
δ
(m, 2H, CH2-9), 1.72 (s, 1H, -OH), 2.14 (s, 3H, CH3-11), 2.27–2.33 (m, 2H, one of CH2-5 and one of
CH2-6), 2.54–2.57 (m, 1H, one of CH2-6), 2.82 (dd, 1H, J = 718.4 and 6.12 Hz one of CH2-5), 2.87 (m, 1H,
H-8), 3.05 (m, 1H, H-7), 4.77 (m, 1H, H-4). 13C NMR (CDCl3),
δ: 204.87 (C-1), 170.61 (C-3), 138.33 (C-2),
71.64 (C-4), 58.60 (C-8), 55.31 (C-7), 44.08 (C-5), 21.97 (C-6), 21.12 (C-9), 13.91 (C-11), 10.53 (C-10). IR
(film, cm−1): 3428 (s), 1702 (s), 1649 (s).

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3.2. Aphid Behavioral Studies
3.2.1. Cultures of Aphids and Plants
The peach potato aphids and th◦e Chinese cabbage Brassica rapa subsp. pekinensis (Lour.) Hanelt
were reared in the laboratory at 20 C, 65% r.h., and L16:8D photoperiod. One to seven days old
apterous females of M. persicae and 3-week old plants with four to five fully developed leaves were used
for experiments. M. persicae were obtained from the laboratory culture maintained at the Department
of Botany and Ecology for many generations since 2008. All experiments were carried out under the
same conditions of temperature, relative humidity, and photoperiod. The bioassays were started at
10:00–11:00 a.m.
3.2.2. Application of Compounds
Each compound was dissolved in 70% ethanol to obtain the recommended 0.1% solution [40].
All compounds were applied on the adaxial and abaxial leaf surfaces by immersing a leaf in the
ethanolic solution of a given compound for 30 s [26,29]. Control leaves of similar size were immersed
in 70% ethanol that was used as a solvent for the studied jasmonates. Experiments were performed 1 h
after the compound’s application to allow for the evaporation of the solvent. Every plant and aphid
were used only once.
3.2.3. Aphid Settling
This bioassay allows the study of aphid host preferences under semi-natural conditions.
Aphids were given free choice between control and treated excised leaves that were placed in a
Petri dish. Aphids were placed in the dish equidistance from treated and untreated leaves, so that
aphids could choose between treated (on one half of a Petri dish) and control leaves (on the other
half of the dish). Aphids that settled, i.e., they did not move and the position of their antennae
indicated feeding [41], on each leaf were counted at 1 h, 2 h, and 24 h intervals after access to the leaf.
Each experiment was replicated eight times (eight replicates, 20 viviparous apterous females/replicate).
Aphids that were moving or not on any of the leaves were not counted. The data were analyzed using
a Student’s t-test (STATISTICA 6.1. package). If aphids showed a clear preference for the leaf treated
with the tested compound (p < 0.05), the compound was described as having attractant properties.
If aphids settled mainly on the control leaf (p < 0.05), the compound tested in the respective choice
test was stated as being a deterrent. From the data thus obtained, the relative index of deterrence (DI)
was calculated: DI = (C-T/C+T) where C was the number of aphids settled on control leaf, T was the
number of aphids settled on the leaf treated with tested compound. The value of DI ranged between 1
(ideal deterrent) and −1 (ideal attractant).
3.2.4. Aphid Probing Behavior
Probing by M. persicae in tissues of plants treated with jasmonates was monitored using the
technique of electronic registration of aphid behavior known as an EPG (electrical penetration graph)
that is frequently employed in insect–plant relationship studies [42,43]. By using the EPG technique,
it is possible to monitor aphid probing and feeding behavior within plant tissues, localize natural
plant resistance factors, and reveal the effect of exogenously applied compounds that may influence
plant–aphid interactions [28,36,44,45]. Aphid decisions whether to leave or remain on the plant and
continue probing and feeding are based mainly on chemical information within plant tissues that is
detected with contact chemoreceptors in the gustatory organ in the pharynx [46]. At the same time,
the alteration of aphid behavior during probing following the exogenous application of xenobiotics
demonstrates indirectly the transcuticular and within-plant transfer of these xenobiotics [44]. The EPG
technique allows a separate analysis of aphid behavior at pre-ingestive (within non-phloem tissues
before the first phloem phase) and ingestive (within the phloem) phases of probing [46]. In the
experimental set-up, aphid and plant are made parts of an electrical circuit, which is completed when

Molecules 2018, 23, 2362
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the aphid inserts its stylets into the plant. A weak voltage is supplied in the circuit, and all changing
electric properties are recorded as EPG waveforms that can be correlated with aphid activities and
stylet position in plant tissues [47]. The parameters describing aphid behavior during probing and
feeding, such as the total time of probing, proportion of phloem patterns, number of probes, etc.,
are good indicators of plant suitability or interference of probing by chemical or physical factors in
plant tissues [48]. Jasmonates were applied to test leaves of intact plants as described earlier. Aphids
were attached to a golden wire electrode with silver paint and starved for 1 h prior to the experiment.
The experiments were repeated 25 times for each jasmonate/aphid combination and each replicate
consisted of a freshly prepared aphid and a plant. Incomplete recordings were rejected from analysis.
The probing behavior of aphids was monitored for 8 h continuously. A Giga-8 DC EPG system with a
1 G
Ω of input resistance (EPG Systems, Wageningen, The Netherlands) was used to record the EPG
waveforms. EPGs were recorded and analyzed using Stylet+ Software (EPG Systems, Wageningen,
The Netherlands). Signals were saved on the computer and the various behavioral phases were
labelled manually using the Stylet+ software. The following EPG patterns were distinguished: np
(non-penetration, when aphid stylets did not have contact with plant tissues), A, B, C, F (pathway
phase—penetration of non-phloem tissues), E1 (salivation into sieve elements), E2 (ingestion of phloem
sap), and G (ingestion of xylem sap). The E1/E2 transition patterns were included in E2. EPG
parameters were calculated manually and individually for every aphid. The waveform patterns that
were terminated by the end of the experimental period (8 h) were not excluded from the calculations.
The relevant information is provided in the explanation to the tables. The mean and standard
errors were subsequently calculated using the EPG analysis Excel worksheet created for this study.
The experimental results were analyzed with a one-tailed Mann–Whitney U-test using the STATISTICA
9.0 package (StatSoft, Tulsa, OK, USA).
4. Conclusions
The behavioral study demonstrated that cis-jasmone (
hydroxyderivatives: (+)-(R)-4-hydroxyjasmone ( ) and (+)-(R)-4-hydroxydihydrojasmone (
epoxyderivatives: ( )-7,8-epoxyjasmone ( ) and 4-hydroxy-7,8-epoxyjasmone ( ), and alkyl-substituted
-lactones: 3,4-dihydro-5-methyl-6-pentyl-2H-pyran-2-one ( ), 5-hydroxy-5-methyl-6-pentyltetrahydro
), and 5-methyl-6-pentyl-1,13-dioxabicyclo[4.1.0] heptan-2-ol (10) impeded aphid
1
), dihydrojasmone (
2), and the
3
4),
±
5
6
δ
7
-2H-pyran-2-one (
9
activity during early stages of probing, at the level of non-phloem tissues, which caused a failure in
finding the food source in plant sieve elements. 5-Methyl-6-pentyl-1,13-dioxabicyclo[4.1.0]heptan-2-
one (8) enhanced the process of plant acceptance by M. persicae. The chemical structure of the studied
compounds had a significant influence on their effect on aphid behavior. The presence of a hydroxy
group in the structure of jasmonates played a key role in this respect, in particular when it was
correlated with the lactone ring. Jasmonate derivatives containing these two structural fragments were
more active biologically than the other compounds studied.
Author Contributions: Conceptualization, A.G., K.D. and B.G.; Methodology, A.G., K.D. and B.G.; Validation,
A.G. and K.D.; Formal Analysis, A.G. and M.P.; Investigation, A.G., M.P. and K.D.; Resources, A.G.; Data Curation,
A.G., K.D. and M.P.; Writing-Original Draft Preparation, A.G. and B.G.; Writing-Review & Editing, A.G. and B.G.;
Visualization, M.P. and A.G.; Supervision, K.D. and B.G.; Project Administration, A.G. and K.D.
Funding: This research received no external funding.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds are not available currently. However, they may be provided
upon request from the authors.
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2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
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