![Typical profiles of electric current generated by an adult housefly placed on a grounded iron plate in a negatively charged insulated conductor (an insulated iron plate, NC-IP) with voltages of −15 (A), −14.5 (B), −14 (C),−12 (D), −10 (E), and −8 kV (F). Arrows 'a' and 'b' indicate the electric current produced by the fly upon attraction to the NC-IP and the subsequent electric current generated by the captured fly, respectively. The total amount of electricity released from the captured fly was determined as the total amount of electric current (TAEC; µA min) generated by the fly, calculated as the area bounded by the x-axis and the profile curve of current generation. Arrow 'c' indicates the time until death of the captured fly. The total amount of electric current (AECD) until fly death was also calculated [24].](https://www.researchgate.net/publication/361409539/figure/fig1/AS:11431281079085897@1660528178185/Typical-profiles-of-electric-current-generated-by-an-adult-housefly-placed-on-a-grounded_Q320.jpg)
![(A) Electrostatic insect sweeper (EIS) used to trap insects resting on greenhouse tomato leaves. (B) Schematic representation of the EIS structure. (C) Schematic representation of the inner EIS structure. (D) EIS capturing whiteflies on leaves. (E) Schematic representation of insect capture on a leaf (plan view). Red and green arrows indicate the directions of insect attraction and leaf-surface sweeping with the EIS, respectively. (F) Whiteflies trapped by the EIS insulated conductor wire. SC, sealing cap; SN, stainless net; SP, spacer; ICW, insulated conductor wire; PVC-P, polyvinylchloride pipe; N-VG, negative voltage generator; SB, storage battery; GR, grip; SDEF, single-charged dipolar electric field; WF, whitefly; LS, leaf surface. [7].](https://www.researchgate.net/publication/361409539/figure/fig3/AS:11431281079085900@1660528178437/A-Electrostatic-insect-sweeper-EIS-used-to-trap-insects-resting-on-greenhouse-tomato_Q320.jpg)
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Citation: Kakutani, K.; Matsuda, Y.;
Nonomura, T.; Toyoda, H. An
Electrostatic Pest Exclusion Strategy
for Greenhouse Tomato Cultivation.
Horticulturae 2022,8, 543. https://
doi.org/10.3390/horticulturae8060543
Academic Editor:
Manuel González-Núñez
Received: 18 May 2022
Accepted: 16 June 2022
Published: 18 June 2022
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4.0/).
horticulturae
Review
An Electrostatic Pest Exclusion Strategy for Greenhouse
Tomato Cultivation
Koji Kakutani 1, Yoshinori Matsuda 2,* , Teruo Nonomura 2,3 and Hideyoshi Toyoda 4
1Pharmaceutical Research and Technology Institute, Anti-Aging Centers, Kindai University,
Osaka 577-8502, Japan; kakutani@kindai.ac.jp
2Laboratory of Phytoprotection Science and Technology, Faculty of Agriculture, Kindai University,
Nara 631-8505, Japan; nonomura@nara.kindai.ac.jp
3Agricultural Technology and Innovation Research Institute, Kindai University, Nara 631-8505, Japan
4Research Association of Electric Field Screen Supporters, Nara 631-8505, Japan; toyoda@nara.kindai.ac.jp
*Correspondence: ymatsuda@nara.kindai.ac.jp
Abstract:
Electrostatic devices generating an electric field (EF) are promising tools for greenhouse
tomato cultivation. In these devices, an EF is generated in the space surrounding an insulated
conductor (IC) that is charged by a voltage generator. Thus, a physical force is exerted on any insect
that enters the EF, as a negatively charged IC (NC-IC) pushes a negative charge (free electrons) out
of the insect body. The insect is polarized positively to be attracted to the NC-IC, and a grounded
metal net (G-MN) repels the insect. This dual function of the apparatus (insect capture and repulsion)
is the core of the electrostatic pest-exclusion strategy. In this study, we applied various innovative
EF-based devices to evaluate their efficacy in greenhouse tomato cultivation. Our objective was to
determine the optimal apparatus for simple, inexpensive construction by greenhouse workers. The
results of this study will contribute to the development of sustainable pest-management protocols in
greenhouse horticulture.
Keywords:
attractive force; electric field; electric field screen; leaf miner; phototactic insect; repulsive
force; shore fly; thrips; whitefly
1. Introduction
In horticulture, insecticide-free greenhouse crop cultivation is a non-chemical com-
ponent of integrated pest management (IPM). This approach has been a major focus for
achieving sustainable pest control because it reduces the occurrence of insecticide-resistant
pests and addresses public pesticide concerns. The main obstacles to the practical imple-
mentation of non-chemical pest control systems are the application of individual methods
to an integrated pest control system at scales larger than the test experiments, and under
variable environmental conditions [
1
]. Physical techniques have potential as effective
supplementary measures against an unlimited range of targets under diverse conditions.
Electrostatic techniques are useful to generate physical barriers as the first step in a pest
management strategy for prevention, avoidance, monitoring, and suppression of pest
populations (the PAMS approach) [2].
Because electrostatic phenomena are less susceptible to biological and environmental
influences, physical pest control measures based on electrostatics are promising under
variable environmental conditions. For example, an electric field (EF) is defined as the
space surrounding an electric charge within which a perceptible force can be exerted
on another electric charge [
3
]. Thus, EF-based devices have been developed as a stable
method for trapping or repelling insect pests. In these devices, the EF is generated in the
space surrounding a conductor that is negatively charged [
4
,
5
]. To produce attractive or
repulsive forces within the EF, the release (discharge) of a negative charge from the charged
conductor must be suppressed by covering the conductor with an insulating material such
Horticulturae 2022,8, 543. https://doi.org/10.3390/horticulturae8060543 https://www.mdpi.com/journal/horticulturae
Horticulturae 2022,8, 543 2 of 20
as polyvinylchloride (PVC). An EF will also form in the space surrounding a positively
charged insulated conductor. Pairing oppositely charged insulated conductors at a definite
interval forms a double-charged dipolar electric field (DDEF) [
5
]. A single-charged dipolar
electric field (SDEF) is formed by placing a negatively charged insulated conductor (NC-IC)
and a grounded metal net (G-MN) within the EF, facing each other [
5
]. The strength of
the force thus generated is determined according to the strength or intensity of the EF,
which is optimized by controlling the voltage applied to the insulated conductor and
the distances between the charged insulated conductor and the G-MN, and between the
oppositely charged paired insulated conductors (pole distance). In the SDEF and DDEF,
the generated force is sufficiently strong that insects that enter the EF cannot escape the
trap. In this study, we examined the efficacy of various apparatuses that produce SDEF
and DDEF for EF-based pest control by using video recordings. These apparatuses have
simple structures and are easily constructed by using inexpensive common materials and
a voltage generator [
5
]. Our objective was to provide basic data for the application and
development of electrostatic techniques for pest control.
Greenhouse tomatoes have several insect pests including the whitefly (Bemisia tabaci
[Gennadius] [Hemiptera: Aleyrodidae]) [
6
–
10
], green peach aphid (Myzus persicae [Sulzer]
[Hemiptera: Aphididae]) [
6
,
7
], western flower thrips (Frankliniella occidentalis [Pergande]
[Thysanoptera: Thripidae]) [
6
,
7
,
10
], tomato leaf miner (Liriomyza sativae Blanchard [Diptera:
Agromyzidae]) [
8
,
10
,
11
], and shore fly (Scatella stagnalis [Fallén]
[Diptera: Ephydridae]) [6,7]
.
In this study, we evaluated the performance of various electrostatic pest control devices by
using some of these pests. The results of this study will contribute to the development of
feasibly EF-based pest control apparatuses for greenhouses.
2. SDEF-Based Capture-and-Kill Insect Trap
2.1. Fabrication of the Device
The first step in EF production is to charge an insulated conductor by using a voltage
generator. In this study, we used a voltage generator powered by a rechargeable lithium
storage battery to enhance an initial voltage (12 V) to a desired voltage within the range
1–20 kV
by using an integrated Cockcroft circuit [
12
] and an integrated transformer. Nega-
tive and positive voltage generators were used to charge an insulated conductor negatively
and positively, respectively (Figure S1) [
5
]. Thus, the voltage-enhanced negative voltage
generator collects negative electricity from a ground and supplies it to a conductor linked
to the voltage generator (Figure S1A). Negative charge accumulates on the surface of the
conductor; an insulating PVC tube with a resistivity of 10
9Ω
cm prevents the conductor
from releasing surface charge (i.e., discharge). The surface charge of the conductor po-
larizes the insulating cover dielectrically: negatively on the outer surface and positively
on the inner surface [
13
]. Finally, a negative surface charge on the insulated conductor
generates an EF in the space surrounding it (Figure S1B). By contrast, a positive voltage
generator pushes free electrons from the linked insulated conductor to a ground, positively
charging the outer surface of the conductor (Figure S1C), which in turn positively charges
the insulating coating through dielectric polarization (Figure S1D) [
13
]. Thus, negative
and positive charges on the surface of an insulating coating each produce an EF in their
surrounding space.
When a grounded non-insulated conductor is placed within an EF produced by the
charged insulated conductor, free electrons in the grounded conductor are pushed to the
ground by the negatively charged insulator surface. As a result, the grounded conductor
facing the charged insulated conductor becomes positively charged through electrostatic
induction [
14
]. Opposite charges on these two conductors form dipoles in the original EF to
produce the SDEF (Figure 1A). In this study, the SDEF was produced by opposing a charged
insulated iron wire and a stainless-steel G-MN consisting of 1.5 mm mesh (Figure 1A) or
a charged insulated (soft PVC-membrane-coated) iron plate to a grounded non-insulated
iron plate (Figure 1B).
Horticulturae 2022,8, 543 3 of 20
Horticulturae2022,8,xFORPEERREVIEW3of20
1A)orachargedinsulated(softPVC‐membrane‐coated)ironplatetoagroundednon‐
insulatedironplate(Figure1B).
Figure1.Single‐chargeddipolarelectricfield(SDEF)producedwithinanEFproducedbyanega‐
tivelychargedinsulatedconductor(NC‐IC)byopposingachargedinsulatedironwiretoa
groundedmetalnet(A)orachargedinsulatedironplatetoagroundednon‐insulatedironplate
(B).N‐VG,negativevoltagegenerator;DP‐I,dielectricallypolarizedinsulatorwithnegativecharge
onitssurface;EF,electricfield;NC‐IW,negativelychargedironwire;NC‐IP,negativelycharged
ironplate;GIN,groundedironnet;GIP,groundedironnon‐insulatedplate[5].
2.2.InsectCapturethroughDischarge‐MediatedPositiveElectrification
IntheSDEF,thenegativechargeoftheNC‐IChasarepulsiveforcetoaninsecten‐
teringtheEFandpushesfreeelectronsoutoftheinsectbodytotheground(Figure2A),
positivelyelectrifyingtheinsectsuchthatitisattractedtotheNC‐IC(Figure2B)[15,16].
Duringthisprocess,freeelectronsarereleasedfromtheinsectbodyduetotheconductiv‐
ityofitsouterprotectivecuticle[17–21].Asanexample,VideoS1showsfouradultinsects
(whitefly,greenpeachaphid,westernflowerthripsandtomatoleafminerfly)being
blownintothespacebetweentheG‐MNandtheNC‐IC,whichconsistsofinsulatediron
wire,followedbyitssuccessfulattractiontotheNC‐IC.
Figure2.Schematicrepresentationofinsectcaptureshowingdischarge‐mediatedpositiveelectrifi‐
cationofaninsectinanSDEF.TheSDEFwasproducedwithintheEFofanNC‐IC.Freeelectrons
wereejectedoutoftheinsectbody,producingpositiveelectrification(A),andthepositivelyelectri‐
fiedinsectwasattractedtotheNC‐IC(B).Redarrowindicatesthedirectionoffreeelectronmove‐
ment.Blackarrowindicatesthedirectionoftheforceattractingthepositivelyelectrifiedinsectto
thenegativelychargedinsulatedconductor.N‐VG,negativevoltagegenerator;DP‐I,dielectrically
Figure 1.
Single-charged dipolar electric field (SDEF) produced within an EF produced by a negatively
charged insulated conductor (NC-IC) by opposing a charged insulated iron wire to a grounded metal
net (
A
) or a charged insulated iron plate to a grounded non-insulated iron plate (
B
). N-VG, negative
voltage generator; DP-I, dielectrically polarized insulator with negative charge on its surface; EF,
electric field; NC-IW, negatively charged iron wire; NC-IP, negatively charged iron plate; GIN,
grounded iron net; GIP, grounded iron non-insulated plate [5].
2.2. Insect Capture through Discharge-Mediated Positive Electrification
In the SDEF, the negative charge of the NC-IC has a repulsive force to an insect entering
the EF and pushes free electrons out of the insect body to the ground (Figure 2A), positively
electrifying the insect such that it is attracted to the NC-IC (Figure 2B) [
15
,
16
]. During
this process, free electrons are released from the insect body due to the conductivity of its
outer protective cuticle [
17
–
21
]. As an example, Video S1 shows four adult insects (whitefly,
green peach aphid, western flower thrips and tomato leaf miner fly) being blown into the
space between the G-MN and the NC-IC, which consists of insulated iron wire, followed
by its successful attraction to the NC-IC.
Horticulturae2022,8,xFORPEERREVIEW3of20
1A)orachargedinsulated(softPVC‐membrane‐coated)ironplatetoagroundednon‐
insulatedironplate(Figure1B).
Figure1.Single‐chargeddipolarelectricfield(SDEF)producedwithinanEFproducedbyanega‐
tivelychargedinsulatedconductor(NC‐IC)byopposingachargedinsulatedironwiretoa
groundedmetalnet(A)orachargedinsulatedironplatetoagroundednon‐insulatedironplate
(B).N‐VG,negativevoltagegenerator;DP‐I,dielectricallypolarizedinsulatorwithnegativecharge
onitssurface;EF,electricfield;NC‐IW,negativelychargedironwire;NC‐IP,negativelycharged
ironplate;GIN,groundedironnet;GIP,groundedironnon‐insulatedplate[5].
2.2.InsectCapturethroughDischarge‐MediatedPositiveElectrification
IntheSDEF,thenegativechargeoftheNC‐IChasarepulsiveforcetoaninsecten‐
teringtheEFandpushesfreeelectronsoutoftheinsectbodytotheground(Figure2A),
positivelyelectrifyingtheinsectsuchthatitisattractedtotheNC‐IC(Figure2B)[15,16].
Duringthisprocess,freeelectronsarereleasedfromtheinsectbodyduetotheconductiv‐
ityofitsouterprotectivecuticle[17–21].Asanexample,VideoS1showsfouradultinsects
(whitefly,greenpeachaphid,westernflowerthripsandtomatoleafminerfly)being
blownintothespacebetweentheG‐MNandtheNC‐IC,whichconsistsofinsulatediron
wire,followedbyitssuccessfulattractiontotheNC‐IC.
Figure2.Schematicrepresentationofinsectcaptureshowingdischarge‐mediatedpositiveelectrifi‐
cationofaninsectinanSDEF.TheSDEFwasproducedwithintheEFofanNC‐IC.Freeelectrons
wereejectedoutoftheinsectbody,producingpositiveelectrification(A),andthepositivelyelectri‐
fiedinsectwasattractedtotheNC‐IC(B).Redarrowindicatesthedirectionoffreeelectronmove‐
ment.Blackarrowindicatesthedirectionoftheforceattractingthepositivelyelectrifiedinsectto
thenegativelychargedinsulatedconductor.N‐VG,negativevoltagegenerator;DP‐I,dielectrically
Figure 2.
Schematic representation of insect capture showing discharge-mediated positive electrifica-
tion of an insect in an SDEF. The SDEF was produced within the EF of an NC-IC. Free electrons were
ejected out of the insect body, producing positive electrification (
A
), and the positively electrified
insect was attracted to the NC-IC (
B
). Red arrow indicates the direction of free electron movement.
Black arrow indicates the direction of the force attracting the positively electrified insect to the nega-
tively charged insulated conductor. N-VG, negative voltage generator; DP-I, dielectrically polarized
insulator with negative charge on its surface; NC-IW, negatively charged iron wire; GIN, grounded
iron net; GM, galvanometer; TI, test insect [5].
Horticulturae 2022,8, 543 4 of 20
The force required to attract an insect to the NC-IC is directly proportional to the
increase in the voltage applied to the insulated conductor. More importantly, free electrons
that are pushed out of the insect body are recorded as a transient electric current by a
galvanometer integrated into the grounded line (Figure 2). Using 15 insect species (8 orders,
15 families, 15 genera; body length, 0.8–5.1 mm), we examined the voltages showing a
100% capture rate for each test insect (Figure 3A) [
22
]. The test insects were individually
transferred onto the EF-side surface of the G-MN by using an insect aspirator to examine
the attraction of the insect to the NC-IC. We detected a linear correlation between body
size and the voltage applied to the insulated conductor, indicating that higher voltages
were required to capture larger insects. The relationship between insect body size and
the electric current released from the insect upon its attraction to the NC-IC is shown in
Figure 3B. In this experiment, the insulated conductor was charged at
−
13.1 kV to obtain
a 100% capture rate for all tested insect species. The results indicated that larger insects
released larger electric currents upon attraction to the NC-IC.
Horticulturae2022,8,xFORPEERREVIEW4of20
polarizedinsulatorwithnegativechargeonitssurface;NC‐IW,negativelychargedironwire;GIN,
groundedironnet;GM,galvanometer;TI,testinsect[5].
TheforcerequiredtoattractaninsecttotheNC‐ICisdirectlyproportionaltothein‐
creaseinthevoltageappliedtotheinsulatedconductor.Moreimportantly,freeelectrons
thatarepushedoutoftheinsectbodyarerecordedasatransientelectriccurrentbyagal‐
vanometerintegratedintothegroundedline(Figure2).Using15insectspecies(8orders,15
families,15genera;bodylength,0.8–5.1mm),weexaminedthevoltagesshowinga100%
capturerateforeachtestinsect(Figure3A)[22].Thetestinsectswereindividuallytrans‐
ferredontotheEF‐sidesurfaceoftheG‐MNbyusinganinsectaspiratortoexaminethe
attractionoftheinsecttotheNC‐IC.Wedetectedalinearcorrelationbetweenbodysizeand
thevoltageappliedtotheinsulatedconductor,indicatingthathighervoltageswererequired
tocapturelargerinsects.Therelationshipbetweeninsectbodysizeandtheelectriccurrent
releasedfromtheinsectuponitsattractiontotheNC‐ICisshowninFigure3B.Inthisex‐
periment,theinsulatedconductorwaschargedat−13.1kVtoobtaina100%captureratefor
alltestedinsectspecies.Theresultsindicatedthatlargerinsectsreleasedlargerelectriccur‐
rentsuponattractiontotheNC‐IC.
Figure3.Relationshipsbetweeninsectbodysizeandminimumvoltagefor100%insectcapture(A)
andinsectbodysizeandthemagnitudeoftheinsectelectriccurrentat13.1kV(B).a,Germancock‐
roach;b,riceweevil;c,greenriceleafhopper;d,greenhouseshorefly;e,adzukibeanweevil;f,red
flourbeetle;g,Asiantigermosquito;h,greenpeachaphid;i,commonclothesmoth;j,bathroomfly;k,
westernflowerthrip;l,orientaltermite;m,tomatoleafminerfly;n,booklouse;o,whitefly[22].
TheforcegeneratedintheEFisfundamentallyinfluencedbytheappliedvoltageand
poledistance,withlongerdistancesrequiringhighervoltages.Table1showsthevoltages
requiredtocapturealltestinsectsforarangeofdistancesbetweentheNC‐ICandG‐MN.
Table1.Voltage(kV)requiredtocapturealltestinsectpestsatdifferentpoledistancesinthe
single‐chargeddipolarelectricfield(SDEF).
InsectPestsTestedPoleDistance(mm)
a
5710
Whiteflies2.74.26.2
Greenpeachaphids3.24.56.5
Westernflowerthrips4.26.37.3
Tomatoleafminerflies3.65.16.2
Shoreflies4.85.97.5
Figure 3.
Relationships between insect body size and minimum voltage for 100% insect capture
(A) and insect body size and the magnitude of the insect electric current at −13.1 kV (B). a, German
cockroach; b, rice weevil; c, green rice leaf hopper; d, greenhouse shore fly; e, adzuki bean weevil;
f, red
flour beetle; g, Asian tiger mosquito; h, green peach aphid; i, common clothes moth; j, bathroom
fly; k, western flower thrip; l, oriental termite; m, tomato leaf miner fly; n, book louse; o, whitefly [
22
].
The force generated in the EF is fundamentally influenced by the applied voltage and
pole distance, with longer distances requiring higher voltages. Table 1shows the voltages
required to capture all test insects for a range of distances between the NC-IC and G-MN.
Table 1.
Voltage (
−
kV) required to capture all test insect pests at different pole distances in the
single-charged dipolar electric field (SDEF).
Insect Pests Tested
Pole Distance (mm) a
5 7 10
Whiteflies 2.7 4.2 6.2
Green peach aphids 3.2 4.5 6.5
Western flower thrips 4.2 6.3 7.3
Tomato leaf miner flies 3.6 5.1 6.2
Shore flies 4.8 5.9 7.5
aDistance between the charged insulated conductor wire and grounded metal net.
Horticulturae 2022,8, 543 5 of 20
2.3. Insect Death Caused by the Release of Free Electrons during Continuous Capture by the NC-IC
The field strength of the SDEF is determined by the applied voltage and pole distance.
Uneven pole distance can occur as a structural fault in the field produced by the NC-IC
(insulated iron wire) and G-MN (Figure 1A). By contrast, the dipolar field produced by
a pair of identical iron plates has an even distance along the entire face of the plate pair
(Figure 1B), such that current generation from the insect can be examined without positional
influence. By using this apparatus and the adult housefly Musca domestica (Linnaeus)
(Diptera: Muscidae), which is sufficiently large to generate significant electric current, we
traced current generation by the housefly throughout the capture process [
23
,
24
], from
its attraction to the NC-IC (Figure 4A) to its confinement to the charged plate (Figure 4B).
Figure 4C shows a typical profile of the electric current generated by the adult housefly. The
total amount of electric current generated by the housefly is a crucial factor in its survival.
Horticulturae2022,8,xFORPEERREVIEW5of20
aDistancebetweenthechargedinsulatedconductorwireandgroundedmetalnet.
2.3.InsectDeathCausedbytheReleaseofFreeElectronsduringContinuousCapturebytheNC‐IC
ThefieldstrengthoftheSDEFisdeterminedbytheappliedvoltageandpoledis‐
tance.Unevenpoledistancecanoccurasastructuralfaultinthefieldproducedbythe
NC‐IC(insulatedironwire)andG‐MN(Figure1A).Bycontrast,thedipolarfieldpro‐
ducedbyapairofidenticalironplateshasanevendistancealongtheentirefaceofthe
platepair(Figure1B),suchthatcurrentgenerationfromtheinsectcanbeexaminedwith‐
outpositionalinfluence.ByusingthisapparatusandtheadulthouseflyMuscadomestica
(Linnaeus)(Diptera:Muscidae),whichissufficientlylargetogeneratesignificantelectric
current,wetracedcurrentgenerationbythehouseflythroughoutthecaptureprocess
[23,24],fromitsattractiontotheNC‐IC(Figure4A)toitsconfinementtothechargedplate
(Figure4B).Figure4Cshowsatypicalprofileoftheelectriccurrentgeneratedbytheadult
housefly.Thetotalamountofelectriccurrentgeneratedbythehouseflyisacrucialfactor
initssurvival.
Figure4.(A,B)Schematicrepresentationofelectriccurrentgenerationbyaninsectuponitsattrac‐
tiontoaninsulatedironplate(NC‐IC)(A)andduringsubsequentconfinementtothechargedplate
(B).Redarrowindicatesthedirectionofmovementoffreeelectronspushedoutoftheinsectbody
bytheNC‐IC.Blackarrowindicatesthedirectionoftheattractiveforcedrawingthepositivelyelec‐
trifiedinsecttothenegativelychargedinsulatedconductor.(C)Typicalprofileofelectriccurrent
generatedbyaninsectplacedonthegroundedironplate.Arrows‘a’and‘b’indicateelectriccurrent
producedbytheinsectuponitsattractiontothenegativelychargedinsulatedironplateandduring
subsequentconfinementtothechargedplate,respectively.Thetotalamountofelectricityreleased
fromtheflywascalculatedasthetotalamountofelectriccurrent(TAEC)(μAmin)generatedby
thefly,accordingtotheareaboundedbythex‐axisandtheplottedcurveofgeneratedcurrent.
AbbreviationsareprovidedinFigure1.
Inthisexperiment,allfliesthatweretransferredtothegroundedplatewerecaptured
bytheNC‐ICat<8kV,suchthatnofliesescapedfromthetrap.Anexampleofcurrent
dischargeforarangeofappliedvoltages(8to15kV)isshowninFigure5.Inthis
experiment,weexaminedchangesinthemagnitudeofelectriccurrentanddurationof
currentgenerationamongthedifferentvoltages.Highervoltagesproducedalargeinitial
currentpeakwithashortduration.Athighervoltages14to15kV),thefliesdiedbefore
currentgenerationended;wecalculatedthelethalamountofelectriccurrent(AECD)as
120μAminforadulthouseflies,withlittlevariationamongindividualhouseflies(Figure
5A–C).Atlowervoltages,currentgenerationendedbeforetheAECDwasreached,and
thefliesremainedalivefor2–6hduringtheconfinedstage(Figure5D–F).Wereleased
thefliesfromthetrapbyswitchingoffthevoltagegeneratorbeforetheydied,andthen
examinedthedegreeofdamagetotheflies,whichwassufficienttokillallflieswithin3
daysaftertheirreleasefromthetrap.
Figure 4.
(
A
,
B
) Schematic representation of electric current generation by an insect upon its attraction
to an insulated iron plate (NC-IC) (
A
) and during subsequent confinement to the charged plate
(B). Red
arrow indicates the direction of movement of free electrons pushed out of the insect body by
the NC-IC. Black arrow indicates the direction of the attractive force drawing the positively electrified
insect to the negatively charged insulated conductor. (
C
) Typical profile of electric current generated
by an insect placed on the grounded iron plate. Arrows ‘a’ and ‘b’ indicate electric current produced
by the insect upon its attraction to the negatively charged insulated iron plate and during subsequent
confinement to the charged plate, respectively. The total amount of electricity released from the fly
was calculated as the total amount of electric current (TAEC) (
µ
A min) generated by the fly, according
to the area bounded by the x-axis and the plotted curve of generated current. Abbreviations are
provided in Figure 1.
In this experiment, all flies that were transferred to the grounded plate were captured
by the NC-IC at <
−
8 kV, such that no flies escaped from the trap. An example of cur-
rent discharge for a range of applied voltages (
−
8 to
−
15 kV) is shown in Figure 5. In
this experiment, we examined changes in the magnitude of electric current and duration
of current generation among the different voltages. Higher voltages produced a large
initial current peak with a short duration. At higher voltages 14 to
−
15 kV), the flies
died before current generation ended; we calculated the lethal amount of electric current
(AECD) as
120 µA min
for adult houseflies, with little variation among individual house-
flies
(Figure 5A–C)
. At lower voltages, current generation ended before the AECD was
reached, and the flies remained alive for 2–6 h during the confined stage (Figure 5D–F). We
released the flies from the trap by switching off the voltage generator before they died, and
then examined the degree of damage to the flies, which was sufficient to kill all flies within
3 days after their release from the trap.
Horticulturae 2022,8, 543 6 of 20
Horticulturae2022,8,xFORPEERREVIEW6of20
Figure5.Typicalprofilesofelectriccurrentgeneratedbyanadulthouseflyplacedonagrounded
ironplateinanegativelychargedinsulatedconductor(aninsulatedironplate,NC‐IP)withvoltages
of15(A),14.5(B),14(C),12(D),10(E),and8kV(F).Arrows‘a’and‘b’indicatethe
electriccurrentproducedbytheflyuponattractiontotheNC‐IPandthesubsequentelectriccurrent
generatedbythecapturedfly,respectively.Thetotalamountofelectricityreleasedfromthecap‐
turedflywasdeterminedasthetotalamountofelectriccurrent(TAEC;μAmin)generatedbythe
fly,calculatedastheareaboundedbythex‐axisandtheprofilecurveofcurrentgeneration.Arrow
‘c’indicatesthetimeuntildeathofthecapturedfly.Thetotalamountofelectriccurrent(AECD)
untilflydeathwasalsocalculated[24].
Thus,discharge‐mediatedpositiveelectrificationeffectivelytrappedinsectswithin
theSDEFandkilledthemthroughthelossofelectricityfromtheinsectbody.Theseresults
demonstratethattheSDEF‐generatingtrap‐and‐killdevicecanbeusedasaninsecttrap
forphysicalpestcontrol.Kakutanietal.[22]reportedthatallinsectsof15speciestested
weresuccessfullykilledduringcapturebythesameapparatus.Thetargetpestsforgreen‐
housetomatoesmainlyincludewhitefly,thrips,wingedandwinglessaphids,leafminers,
andshoreflies.Theseinsectscanpassthroughaconventional,woven,insect‐proofnet
withameshsizeofapproximately1.5mm.TheapplicationoftheSDEFapparatusde‐
scribedinthissectioncankillinsectsatlowappliedvoltages(1to4kV)andwithina
shortperiodoftime(1–2h)[24].Theseresultsstronglysupporttheuseofthisapparatus
fornon‐chemicalgreenhousepestcontrol.
2.4.FabricationofanElectrostaticSoilCover(ESC)toTrapEmergingAdultLeafMiners
ThefirstSDEF‐producingdeviceappliedforpestcontrolwasanESCdesignedto
trapadulttomatoleafminersemergingfromundergroundpupae[11].Leafminerlarvae
hatchfromeggsdepositedontheleafsurface,wheretheyeatleaftissues,andthenfallto
thegroundandcrawlunderthesoiltopupate;theadultfliesemergeandovipositeggs
onahostplant.Thislifecycleallowspersistentinfestationofgreenhousetomatoes[25].
TheESCwasdevelopedtocoversoilbedsinagreenhouse;itsstructure(Figure6A)con‐
sistsoftwosetsofironrodsweldedtoanironframe.ThefirstsetiscoatedwithaPVC
membraneandlinkedtoavoltagegeneratortosupplyanegativechargetotheironrods,
whereasthesecondremainsuninsulatedandislinkedtoagroundline.Eachsetofiron
Figure 5.
Typical profiles of electric current generated by an adult housefly placed on a grounded
iron plate in a negatively charged insulated conductor (an insulated iron plate, NC-IP) with voltages
of
−
15 (
A
),
−
14.5 (
B
),
−
14 (
C
),
−
12 (
D
),
−
10 (
E
), and
−
8 kV (
F
). Arrows ‘a’ and ‘b’ indicate the
electric current produced by the fly upon attraction to the NC-IP and the subsequent electric current
generated by the captured fly, respectively. The total amount of electricity released from the captured
fly was determined as the total amount of electric current (TAEC;
µ
A min) generated by the fly,
calculated as the area bounded by the x-axis and the profile curve of current generation. Arrow ‘c’
indicates the time until death of the captured fly. The total amount of electric current (AECD) until
fly death was also calculated [24].
Thus, discharge-mediated positive electrification effectively trapped insects within
the SDEF and killed them through the loss of electricity from the insect body. These results
demonstrate that the SDEF-generating trap-and-kill device can be used as an insect trap for
physical pest control. Kakutani et al. [
22
] reported that all insects of 15 species tested were
successfully killed during capture by the same apparatus. The target pests for greenhouse
tomatoes mainly include whitefly, thrips, winged and wingless aphids, leaf miners, and
shore flies. These insects can pass through a conventional, woven, insect-proof net with
a mesh size of approximately 1.5 mm. The application of the SDEF apparatus described
in this section can kill insects at low applied voltages (
−
1 to
−
4 kV) and within a short
period of time (1–2 h) [
24
]. These results strongly support the use of this apparatus for
non-chemical greenhouse pest control.
2.4. Fabrication of an Electrostatic Soil Cover (ESC) to Trap Emerging Adult Leaf Miners
The first SDEF-producing device applied for pest control was an ESC designed to trap
adult tomato leaf miners emerging from underground pupae [
11
]. Leaf miner larvae hatch
from eggs deposited on the leaf surface, where they eat leaf tissues, and then fall to the
ground and crawl under the soil to pupate; the adult flies emerge and oviposit eggs on a
host plant. This life cycle allows persistent infestation of greenhouse tomatoes [
25
]. The
ESC was developed to cover soil beds in a greenhouse; its structure (Figure 6A) consists of
two sets of iron rods welded to an iron frame. The first set is coated with a PVC membrane
and linked to a voltage generator to supply a negative charge to the iron rods, whereas the
second remains uninsulated and is linked to a ground line. Each set of iron rods is offset in
a zigzag pattern to form the SDEF between the iron rods (Figure 6B). The ESC was placed
Horticulturae 2022,8, 543 7 of 20
on a soil bed to capture adult leaf miners at a voltage of
−
4 kV as they emerged from the
soil surface and jumped into the space of the ESC [
11
]; the successful operation of the ESC
is shown in Video S2.
Horticulturae2022,8,xFORPEERREVIEW7of20
rodsisoffsetinazigzagpatterntoformtheSDEFbetweentheironrods(Figure6B).The
ESCwasplacedonasoilbedtocaptureadultleafminersatavoltageof4kVasthey
emergedfromthesoilsurfaceandjumpedintothespaceoftheESC[11];thesuccessful
operationoftheESCisshowninVideoS2.
Figure6.Diagramofanelectrostaticcovering(EC)tocaptureadulttomatoleafminerfliesemerging
fromundergroundpupae(A)andanSDEFformedbetweennegativelycharged,insulatedironrods
andgrounded,non‐insulatedironrods(cross‐sectionalview)(B).Redarrowindicatesthepathofa
leafminerthatemergedfromapupainasoil.GN‐IF,groundednon‐insulatedironframe;CI‐IF,
charged,insulatedironframe;N‐IR,non‐insulatedironrod;I‐IR,insulatedironrod;VG,voltagegen‐
erator;SDEF,single‐chargeddipolarelectricfield;SP,spacer,UP,undergroundpupa;SL,soil.[11].
3.Single‐ChargedDipolarElectricFieldScreen(SDScreen)
3.1.AvoidanceoftheSDEFbyInsects
Inapreviousstudy,weexaminedtheabilityofanSDEF‐producingapparatusto
capturewhiteflies[26].Eventually,whitefliesthatwereplacedontheEF‐sidesurfaceof
theG‐MNwerestronglyattractedtotheNC‐IC,whichconsistedofaninsulatedironwire
(Figure7A),whereasthoseplacedontheoutsidesurfaceofthenetinsertedtheirantennae
intheSDEFandavoidedenteringit(Figure7B).
Figure7.Schematicrepresentationofinsectcapture(A)andrepulsion(B)afterinsectplacementon