Selected Abiotic and Biotic Environmental Stress Factors Affecting Two Economically Important

18 Pages·2016·1.15 MB·English

by  Allan T. Showler

agronomy
Review
Selected Abiotic and Biotic Environmental Stress
Factors Affecting Two Economically Important
Sugarcane Stalk Boring Pests in the United States
AllanT.Showler
USDA-ARSKnipling-BushlandU.S.LivestockInsectsResearchLaboratory,2700FredericksburgRoad,Kerrville,
TX78028,USA;[email protected];Tel.:[phone]
AcademicEditor:HerbCutforth
Received:11October2015;Accepted:21January2016;Published:1February2016
Abstract: Sugarcane, Saccharum spp., in the United States is attacked by a number of different
arthropod pests. The most serious among those pests are two stalk boring moths in the Family
Crambidae: thesugarcaneborer,Diatraeasaccharalis(F.),andtheMexicanriceborer,Eoreumaloftini
(Dyar). Thetwospeciesareaffectedbyabioticandbioticenvironmentalstressfactors. Waterdeficit
andexcessivesoilnitrogenalterphysicalandphysiochemicalaspectsofthesugarcaneplantthatmake
thecropincreasinglyvulnerabletoE.loftini. Weedgrowthcanbecompetitivewithsugarcanebutit
alsosupportsenhancedabundancesanddiversityofnaturalenemiesthatcansuppressinfestationsof
D.saccharalis.Inaninstancewherethestalkborerisconsideredastressfactor,proximityofvulnerable
cropstosugarcanecaninfluencelevelsofE.loftiniinfestationofsugarcane. Theadverseeffectsof
eachstressfactor,intermsofstalkborerattack,canbereducedbyadoptingappropriatecultural
practices,suchasadequateirrigation,judicioususeofnitrogenfertilizer,usingnoncompetitiveweed
growth,andnotplantingvulnerablecropsnearsugarcanefields. Understandingtherelationships
betweenstressfactorsandcroppestscanprovidevaluableinsightsforplantbreedersandtoolsfor
incorporationintointegratedpestmanagementstrategies.
Keywords:Saccharum;weeds;Diatraeasaccharalis;Eoreumaloftini;Mexicanriceborer;sugarcaneborer;
soil;vegetationaldiversification;drought;waterdeficit;corn;maize;resistance;cultivars;cultural
practices;irrigation;nitrogen
1. ThePlant
Sugarcane, Saccharum spp., is a perennial crop cultivated on «20 million ha in tropical and
subtropicalregionsofmorethan100countries[1–3]. Annualyieldintermsofstalksis«1325million
tonsharvestedforsugar,rum,chemicals,andenergy[2,4–7].IntheUnitedStates,sugarcaneproduction
occursmainlyinFlorida,Louisiana,Texas,andHawaii[8,9]. In2014,Floridacultivated«160,300ha
and harvested «15.2 million tons of sugarcane, Louisiana cultivated «156,000 ha and produced
«11.5milliontons,Texasgrew«13,400haandharvested«1.2milliontons,andHawaiihad«6800ha
thatproduced«1.3milliontons[8].
Thecropisvegetativelypropagatedbyplacingcuttingsandwholestalksinfurrowsandcovering
themwithsoil. Aftereachharvesttheregrowth,orratoon,growsfromthestubbletobeharvestedthe
followinggrowingseason. Insomeplacesitispossibletoharvest20successiveratooncropsfroma
singleplanting[10],butadverseenvironmentalstressfactorsincludingweedcompetition,stalkborer
injury,pathogeninfection,lowwintertemperatures,waterdeficit,poorsoilaerationanddrainage,and
weakcultivargenotypesdiminishproductivityfromoneseasontothenext(termed“stubbledecline”),
commonlylimitingratoonproductiontoonlyoneortwoseasons[11–13].
Agronomy2016,6,10;doi:10.3390/agronomy6010010 www.mdpi.com/journal/agronomy
Agronomy2016,6,10 2of18
2. TheStalkBorers
Injurytothecropinflictedbyherbivorousarthropodsrepresentsabioticstresstothesugarcane
plant. Manyoftheabioticandbioticfactorsdiscussedbelow(i.e.,waterdeficit,weedcompetition,
soilnitrogen)canexertstressonthesugarcaneplantwhichmightaffecttheherbivoreandtheamount
of damage it causes. Among the herbivorous arthropods that attack sugarcane are stalk boring
insects,thesugarcaneborer,Diatraeasaccharalis(F.),andtheMexicanriceborer,Eoreumaloftini(Dyar)
(bothLepidoptera: Crambidae)arethemosteconomicallyimportanttosugarcaneproductioninthe
UnitedStates[14].
Diatraea saccharalis arose in tropical areas of the Western Hemisphere and it invaded the
UnitedStatesthroughLouisianain1855[14]. ThepestisnowestablishedalongtheUnitedStates’
Gulf Coast from south Texas to southern Florida, the Caribbean, and Latin America from Mexico
to subtropical parts of northern Argentina [14]. Other host plants are maize, Zea mays L.; rice,
OryzasativaL.;sorghum,Sorghumbicolor(L.)Moench;andsudangrass,Sorghumbicolor(L.)Moenchssp.
drummondi (Nees ex Steud.) de Wet and Harlan used as livestock forage, and large-diameter
graminaceousweedsincludingJohnsongrass,Sorghumhalepense(L.)Pers.,Paspalumspp.,Panicumspp.,
Holcus spp., and Andropogon sp. [15–18]. In the United States, larvae mostly overwinter in weedy
grassesandadultsemergeinAprilandMay,followedby4–5nonsynchronousgenerationsthrough
autumn [19,20]. Numbers of adults in sugarcane decline during mid-summer [21]. A summer
generationrequires25–40daystocomplete,andtheinsectundergoesaformofdormancyduringcool
wintermonths[19].
Diatraeasaccharalisisa“plantvigorinsect”thatisattractedtoplantsgrowingvigorously. Thepest
ovipositsonnewleavesandnewinternodes,theflatovaleggslaidingroupsof2to>80[14]mostly
on exposed upper and lower surfaces of leaves, particularly near the top to the plant [14]. Hence,
theeggstageisvulnerabletoacomplexofeggpredatorsandparasites[14,22]. Forlarvaerearedon
sugarcaneandmaize,averagefecundityis«700eggs,butthisdeclineswhenlarvaearerearedon
other host plants, including johnsongrass [23]. First instars tend to feed on leaf tissue, sometimes
tunnelingdirectlyintothemidrib;secondandthirdinstarsboreintothestalk(manymoveupthestalk
beforetunnelinginside)[19,24]. Duringwarmseasonslarvaldevelopmentusuallyrequires25–30days
(30–35daysincoolweather)anddevelopmenthaltswhencoldwintertemperaturesforcetheinsect
tooverwinterandsometimestobedormant,ofteninweeds[25]. Pupationoccursinachamberthat
thelarvachewswithinthestalk,athin“window”ofplanttissueremainingasabarriertopredators,
parasites, and insecticides [14]. Adults emerge from the pupae in 8–9 days (up to 22 days in cool
weather). Moths are yellow or straw-colored with male and female wingspans of 18–28 mm and
27–39mmwingspans,respectively[14]. Theforewingismarkedwithseveralbrownlengthwiselines
andthemalehindwingisduskycomparedtothewhitefemalehindwing. Duringthe3–8dayadult
stage,flightandovipositionmainlyoccurafterdark[14].
Tunnelinginmaturesugarcanestalksweakens,lodges,andkillsuppergrowthand,intheinner
whorlofyoungplants,tunnelingcauses“deadheart”(generallydoesnotresultinsugarcaneplant
biomass and sugar yield losses) [19]. Heavy infestations can result in substantial stalk damage,
diminishing juice quantity and purity, reducing sucrose yield by 10%–20% [14,25]. The larval
tunnelsfurthercontributetoproductionlossesbyprovidingportalsofentryforinfectionbyredrot,
ColletrotrichumfalcatumWent,andotherfungithatweakenordestroystalktissueandbreakdown
sugar[26–29]. Ulloaetal.[30]reportedthatanaverageofoneboredinternodeperstalkresultsin
2.5 kg less sugar per ton of harvested sugarcane. While D. saccharalis is presently the key pest of
sugarcaneinLouisiana[31–33],itsprevalencemightdeclineonceE.loftinipopulationsincreaseand
becomestabilizedthere. InsouthTexas,E.loftinisupplantedD.saccharalisasthekeypestofsugarcane
soonafteritsarrivalfromMexicointheearly1980s[34–36].
ControlofD.saccharalisreliesmostlyoninsecticideapplicationstriggeredbyreachinganeconomic
injurythreshold[14,32]. Althoughbiologicalcontrolusingindigenousandexoticparasitoidwasps
and parasitic flies has met with some success in Florida [37], it has been less effective elsewhere
Agronomy2016,6,10 3of18
in the United States [14]. Entomopathogens such as Beauveria bassiana (Balsamo) Vuillemin and
Metarhiziumanisopliae(Metsch.) SorokwereunabletosuppressD.saccharalispopulationsunderfield
conditions[38,39],andalthoughBacillusthuringiensisBerlinerwasreportedtoreduceD.saccharalis
injurytosugarcanestalksby75%[40],ithasnotbeenadoptedbygrowers. Anotherformofbiological
control,conservationofnaturalenemies,islinkedwithbioticenvironmentalstressfactorsandcanbe
enhancedbyusingcertainculturalpractices. Also,somesugarcanecultivarsexhibitresistancetraits
thatofferdifferentdegreesofprotection[14].
EoreumaloftiniisamajorsugarcanepestindigenoustowesternMexico[26,41]. Firstdetectedin
theUnitedStatesintheLowerRioGrandeValleyofsouthTexasin1980[42–44],theinsectinvadedthe
riceproducingareasofeastTexasby1989[35,45,46]andLouisianaricein2008[47,48]. Byearly2015
E.loftinihadspreadtoriceandsugarcaneineightparishesofsouthernLouisiana[36]. Oneadultwas
trappedinFloridainMarch2012andasoflateDecember2013moreadultshavebeentrappedinLevy
andMarioncountiesandlarvaeandpupaeweredetectedinfallpanicum,Panicumdichotomiflorum
Michx[49,50]. Eoreumaloftinilarvaeandpupaehavebeenfoundinatleast17speciesofgraminous
weedsandsixcropspecies(foralistoftheknownhostplantsseeShowleretal. 2011[51]). Cropsmost
pronetoattackarerice,sugarcane,maize,sorghum,andsomesorghumandsudangrasshybridsused
forlivestockforageandfeed[14,51–53].
Onsugarcane, E.loftinimostlyovipositswithinfoldsalongtheedgesofdryleaves, although
eggsarealsodepositedinfoldedgreenlivingtissueifitisavailable[54]. Ovipositionoccursrelatively
low on the plant; 96% of the eggs are located between the soil surface and ď80 cm above the soil
surface[55].Eggclustersrangefrom5to>80eggs[55].Earlyinstarsfeedonleaftissueandunderfresh
leafsheaths,andsomeboreintotheleafmidrib;laterinstarstunneldirectlyintothemainstalk[56].
Internodesaremostpronetoattackduringtheirfirst70daysofgrowth[57],althougholderinternodes
are also vulnerable as are new internodes near and at the plant’s apex. Tunnels within sugarcane
stalksarehorizontalandvertical(D.saccharalistunnelsaremostlyvertical)andsopackedwithfrass
that larvae are protected from predators and parasitoids [14,47,53]. Like D. saccharalis, late instars
chewachamberinsidethestalkandpupationoccursbehindaplanttissue“window”[14]. Adults
arestraw-coloredandtheirunmarkedwingsaredelta-shaped. InthesubtropicalLowerRioGrande
ValleyofTexas,E.loftini’slifecycleoccursover30–45days,and4–6asynchronousgenerationsare
producedeachyear[29,34]. Between«260and400eggscanbeproducedbyafemale[34]andalllife
stagescanbefoundthroughouttheyear[29,55,58]. SubstantialnumbersofadultE.loftiniemerge
frommaizeinnorthernTamaulipas,Mexico,duringFebruary,andpopulationsremainrelativelyhigh
throughmidsummer[29]. PeakflightactivityintheTexascoastalbendareaoccursinMarchandApril,
andagaininthefall[58].
Protectionfromnaturalenemiesandmanyinsecticidesinsidepluggedtunnelscontributedtoward
thepest’srapidpopulationexpansioninsouthTexas,whereE.loftinireplacedD.saccharalisasthe
keysugarcanepest[34,59]. StalkinjuryfromE.loftinitunnelingdiminishessugaryieldandheavy
infestationscanstuntandlodgestalkssoseverelythatharvestiseconomicallyimpractical[29,34,47,60].
InsouthTexas«20%ofsugarcaneinternodeswerereportedashavingbeendamagedparticularlyby
E.loftini[61]andinadditiontothedamagecausedbytunnels,theentryandexitholesareportals
ofinfectionbyredrot. Larvalpopulationdensitiesgenerallydonotexceedonelarvapersugarcane
stalkintheLowerRioGrandeValley[62]although50%–80%boredinternodeshavebeenreportedon
somecultivarsinTexas[42,43,63]. Estimatesofpercentagesugaryieldlossforeverypercentageof
boredinternodeshaverangedfrom0.5%to1.3%perha[61,64]. EconomiclossresultingfromE.loftini
injury to south Texas sugarcane has been reported as being US $575–$690 per hectare [56,60] and
US$10–$20millionannually[34,61]. AneconomiclossprojectionforLouisianasugarcanethatmight
becausedbyE.loftinionceitbecomesfullyestablishedamountedtoUS$220million[35]. Economic
projectionsforFloridaarenotavailable.
EarlyattemptstouseinsecticidesagainstE.loftinihavefailedtoincreasesugarcaneproductionin
southTexas[60,61]andE.loftinisprayswerediscontinuedduringthe1990s[34]. Morerecentresearch
Agronomy2016,6,10 4of18
revealed that some relatively new insecticides can exert acceptable levels of control [65], but their
adoptionforuseagainstE.loftinihasnotbeenwidespread. Intermsofclassicalbiologicalcontrol,
«27indigenousandexoticparasitoidwaspsandparasiticflieshavebeenreleasedtocombatE.loftini
intheLowerRioGrandeValleywithoutsuccess[14,53]. Variousentomopathogensandentomogenous
nematodeshavebeentriedandtheyalsofailedunderfieldconditions[14,34,39]. Plantingresistant
sugarcane cultivars is another way of protecting crop yields against pests, and some cultivars of
sugarcanethatofferdegreesofresistanceagainstE.loftiniarebecomingavailableandnewresistance
factorshavebeenidentified[14,53,63].Althoughsomeculturalpractices(e.g.,plowingdownsugarcane
stubbleinfallowfieldsandselectingoptimalplantingdates)havebeensuggested[14,53],theyhave
not been implemented for E. loftini management. Other cultural tactics related to environmental
factors (discussed in the next two sections) aim to reduce E. loftini damage to sugarcane, but it is
likelythattheseexamplesdonotrepresentallpossiblewaysofmanipulatingenvironmentalfactors
toachievedesirablelevelsofsuppression. Researchhasidentifiedtwoabioticenvironmentalstress
factorsandthreebioticenvironmentalstressfactorsthatcanbemodifiedwiththegoalofreducing
E.loftiniinfestations.
3. AbioticEnvironmentalStressFactors
3.1. WaterDeficitorDroughtStress
A variety of abiotic factors, some of which induce plant stress, can affect herbivorous pests,
includingtemperature,relativehumidity,andphotoperiod,butthesecannotorarenotdeliberately
manipulatedusingculturalpracticesinfield-growncommercialsugarcane. Whilemoderatedrought
stressisharmfultosomeherbivorousarthropods,itcanalsoincreasepopulationsofmanyherbivorous
arthropodsthatinflictcorrespondinglymoreinjurytoacropthatisalreadystressedandpossibly
damaged from the effects of water deficit or from other pests [66]. Drought-enhanced host plant
suitability for such insects is typically followed by declining suitability as the stress becomes
increasinglysevere[67]. Thedecliningsuitabilityoccursbecauseofinsufficientwaterforthepest’s
requirementsandbecauseofhostplanttissuedesiccation,necrosis,andsenescence[66].
Waterdeficitresultsingreaterabundancesofdryleaftissueonsugarcanestalksthanonstalks
where sugarcane is grown under well-watered conditions [68,69]. Numbers of E. loftini eggs on
sugarcane plants have been positively associated with numbers of dry leaves [69,70] which curl
or fold at the edges. A laboratory experiment demonstrated that, given a choice between folded
greensugarcaneleaves,flatdrysugarcaneleaves,andfoldedpaperapproximatelythesamecolor
asdrysugarcaneleaftissue,eggswerealmostexclusivelydepositedonthefoldedgreenleaves[54].
Whenfoldedgreenleaveswerepresentedalongsidedryfoldedleaves,thedryleaveswereusedfor
oviposition[54].Hence,drynessandfoldsarebothcharacteristicsofsugarcaneleavesthatarepreferred
byE.loftiniforoviposition[54]. Agreenhouseno-choicecageassayusingpottedsugarcaneplants
fromwhichdryleaffoldsweretrimmedawaywithscissorshad93.8%fewereggsthannontrimmed
plants(Figure1)[54]. Delayingtheonsetofleafsenescenceandreducingthequantityofdriedleaves
bymaintainingadequatesoilmoisturewillminimizethedevelopmentofsugarcaneleafcharacteristics
that are preferred as oviposition sites. Delaying water deficit-associated leaf drying by judicious
irrigationislikelytoprotectsugarcanefromearlyandpossiblymidseasoninfestationsthattypically
injurethelowerinternodes.
Even after soil dries, normal evapotranspiration rates in most plants often continue for some
time [71] by accumulating free amino acids, especially proline, and other organic solutes as
osmoregulants [72]. Osmotic stress in plants involves several interconnected molecular pathways
thattransmitsignalsandproducestress-responsemetabolites[73,74],andgenetranscriptsassociated
withsignalingcanbeup-ordown-regulatedwithinminutesofstressinduction[75,76]. Asdrought
conditionscontinue,plantsoftenhaverelativelylowosmoticpotential[77–79],heightenedoxidative
stress [80,81], and to reduce water loss to the extent possible, accumulations of osmolytes such as
Agronomy2016,6,10 5of18
antioxidants,aminoacids,carbohydrates,andinorganicions,alteringtheattractivenessandnutritional
value of the plant to herbivorous arthropods [68–70,82]. Chemical cues (semiochemicals) emitted
byplants,frequentlyinvolvingvolatiles,haveamajorroleinhostplantselectionandutilizationby
herbivorousarthropods[83–90].
Agronomy 2016, 6, 10  5 of 18 
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FigurFeig1u.reM 1.e Manea(n˘ (±S SEE)) nnuummbbeerrss ofo Ef. Elo.ftilnoif tlainrvialla ernvtaryl heonltersy pehro sluegsarpcearnes sutaglakr icna gnreeesnthaolkusien nog‐rceheonicheo use
no-chcoaigcee acsasgayesa wsshaeyres twheh ceurrelst hanedc uforlldssa anlodnfgo tlhdes eadlgoensg oft hderye ldeagfe tsisosufed wryerlee aefxctiissesdu,e dwrye lreeaveexsc wiseerde, dry
placed on the cage floor at a sort of “mulch”, or plants were left intact and without “mulch” as a 
leaveswereplacedonthecageflooratasortof“mulch”,orplantswereleftintactandwithout“mulch”
control; different letters over bars indicate significant differences (p < 0.05) [54]. 
asacontrol;differentlettersoverbarsindicatesignificantdifferences(p<0.05)[54].
The preference of E. loftini to oviposit on drought stressed sugarcane [14,53,68–70] was 
Tdheemopnrsetrfaetreedn cwehoenf Ea .sulogfatirncainteo couvltiivpaors irtesoisntandtr otou gEh. tlosfttirneis s(Led 03s‐u37g1a)r cuanndeer [1w4e,5ll3‐i,r6r8ig–a7t0e]d was
democnosntrdaittieodnsw wheans afosuungda rtoca bnee csuusltcievpatribrlees iusntadnert tdorEou.lgohftti ncoin(Ldi0ti3o-n3s7 1()uupn tdoe 8r8w%e lbl-oirrerdig aintteedrncoodnedsi)t ions
was f[o1u4,n5d3,6t3o,9b1e]. Rsueascye‐Jpotniebsl eet ualn. d[6e8r] rderpoourtgehdt thcoatn wdeitlil‐oirnrsig(autepd tsoug8a8r%canbeo wreads 4in4%te rlensos dsuessc)e[p1t4ib,5le3 ,t6o3 ,91].
E. loftini oviposition and injury to the crop was ≈60% lower than in water deficit stressed sugarcane 
Reay-Jones et al. [68] reported that well-irrigated sugarcane was 44% less susceptible to E. loftini
of susceptible (e.g., LC 85‐384) and resistant (e.g., HoCP 85‐845) cultivars but oviposition preference 
oviposition and injury to the crop was «60% lower than in water deficit stressed sugarcane of
and levels of injury to stalks relative to each cultivar did not change (i.e., HoCP 85‐845 had 44% less 
susceptible (e.g., LC 85-384) and resistant (e.g., HoCP 85-845) cultivars but oviposition preference
injury  than  LCP  85‐384  within  each  irrigation  regime)  [68,70].  Under  controlled  greenhouse 
andlevelsofinjurytostalksrelativetoeachcultivardidnotchange(i.e.,HoCP85-845had44%less
conditions, well‐watered sugarcane plants had 82.8% to 90.2% fewer E. loftini eggs on them than 
injurywtahtaenr dLeCfiPcit8 s5t-r3e8ss4ewd pitlhainntse, alacrhvairl reingtartyi ohnolreesg oinm seta)l[k6s8 w,7e0r]e. 4U4.n4d%e troc 9o4n.5t%ro llleesds agbruenednahnotu, asnedc oadnudlitt ions,
well-wexaitt ehroeldes swuegraer rceadnuecepdl abnyt 6s4h.3a%d t8o2 8.88.%9%t o[6990].. 2A%lthfoeuwgehr EE. .lolfotifntiin pireefgegrss toon dethpeomsit tithsa enggws aotne rdrdye ficit
stressleedaf ptilsasnutes, ,lilvairnvga sluegnatrrcyanheo lleeasf otinsssutea lokf swwateerre d4e4fi.c4i%t sttroes9s4ed.5 %plalnetsss maibguhnt datatrnatc,ta mnodrea deguglt laeyxiintgh oles
werefreemdualceesd thbayn 6n4o.n3s%tretsose8d8 .p9l%an[t6s 9b]e.cAaultsheo ouf gthheE h.eliogfhtitneniepdr ecfoenrcsetnotrdaetiponoss iotfi tnsuetrgigenstos,n sudcrhy ales afrfetei ssue,
livingasmuignaor accaindes tlheaatf atirses euseseonftiwala ftoerr idneseficcti gtrsotrwetshs eadndp ldaenvteslompimgehntta ttot raadcutlmthooroed e[g69g,7l0a]y. iInt gisf peomssailbelse than
that dry leaf tissue might serve as a cue for E. loftini females to oviposit on plants with relatively high 
nonstressedplantsbecauseoftheheightenedconcentrationsofnutrients,suchasfreeaminoacidsthat
accumulations of nutrients beneficial to the resulting larvae [54,69]. Water deficit in nonirrigated field 
areessentialforinsectgrowthanddevelopmenttoadulthood[69,70]. Itispossiblethatdryleaftissue
plots increased accumulations of free nonessential amino acids aspartic acid, proline, serine, and 
mightserveasacueforE.loftinifemalestoovipositonplantswithrelativelyhighaccumulationsof
tyrosine, and essential amino acids histidine, isoleucine, and methionine and intensified pressure 
nutrientsbeneficialtotheresultinglarvae[54,69]. Waterdeficitinnonirrigatedfieldplotsincreased
from E. loftini occurred in those plots [70]. Another field study showed that elevated levels of free 
accummueltahtiioonninseo afnfrde aesnpoarnteics asceindt iinal saumgairncoanaec widesrea sapssaorctiiactaedci wd,itphr oovliinpeo,sisteiornin per,eafenrdentcyer obsyi En.e l,oaftnindi [e6s8s]e. ntial
aminoWaactiedr sdhefiisctiitd iinn ea, gisroeelenuhcoiunsee, wanitdhomute tchoinofnoiunnedainngd fiancttoernss icfioemdmporne stsou frieelfdr osmituaEt.iolonfst iinnidouccceudr rae din
thosespulbosttsa[n7t0ia]l.lyA wnoidthere rrafinegled asntudd lyesssh voawriaebdiltihtya toef lferveea taemdilneov ealcsido facfrceuemmuleatthioionns itnheana nwderaes pdaerteticcteadc idin
sugaricna nfieeldw‐gerreowasns soucgiaatrecdanwe [it6h9]o. Dvirpoousgihtito sntrepsrse efelerveantceed bayccEu.mloufltaitnioin[6s8 o]f. fWreaet gelrudtaemficici taicnida, gglryeceinneh, ouse
withohuistticdoinnefo, uisnoldeiuncginefa, cletuocrisnec,o lmysminoe,n mteothfiioenldinsei, tpuhaetnioynlaslainnidneu,c perdolainseu, sbesrtinane,t tihalrleyonwinied,e tryrroasningee, and
valine, total free essential amino acids in three repeated bioassays (in two of the bioassays, free 
lessvariabilityoffreeaminoacidaccumulationsthanweredetectedinfield-grownsugarcane[69].
alanine also increased) on two cultivars (Table 1 shows data for one of the three bioassays) [69]. 
Droughtstresselevatedaccumulationsoffreeglutamicacid,glycine,histidine,isoleucine,leucine,
In addition to free amino acids, fructose has also been associated with oviposition preference and 
lysine,methionine,phenylalanine,proline,serine,threonine,tyrosine,valine,totalfreeessentialamino
injury to sugarcane stalks [92,93], but water deficit stress has not yet been evaluated for its effects on 
acidsinthreerepeatedbioassays(intwoofthebioassays,freealaninealsoincreased)ontwocultivars
fructose concentrations. 
(Table 1showsdataforoneoftheth reebioassays)[69].Inadditiontofreeaminoacids,fructosehasalso
beenassociatedwithovipositionpreferenceandinjurytosugarcanestalks[92,93],butwaterdeficit
stresshasnotyetbeenevaluatedforitseffectsonfructoseconcentrations.
Agronomy2016,6,10 6of18
Table 1. Mean (˘ SE) picomoles of free amino acid per microliter of sugarcane stalk juice in
twocultivars,L97-128andCP70-321,thatwerewellwateredordroughtstressedinagreenhouse[69].
Treatmentb
FreeAminoAcidsa
L97-128W CP70-321W L97-128D CP70-321D
Alanine 3560˘193b 5836˘1324b 12,257˘1423a 7857˘2277ab
Arginine 1436˘185a 677˘52b 1084˘93a 855˘35a
Asparticacid 2074˘158 2827˘233 2516˘61 2118˘311
Glutamicacid 18˘18b 7˘7b 126˘43a 860˘8a
Glycine 396˘52b 505˘37b 623˘83ab 653˘173a
Histidine 598˘85b 577˘77b 1642˘218a 1995˘273a
Isoleucine 605˘57b 565˘54b 1293˘204a 2858˘47a
Leucine 441˘79b 510˘52b 776˘23a 2639˘88a
Lysine 367˘94b 375˘57ab 650˘80ab 514˘65a
Methionine 225˘20b 239˘64b 771˘88a 1241˘168a
Phenylanaline 258˘43b 226˘49b 908˘88a 1008˘88a
Proline 558˘36b 518˘99b 1198˘89a 4062˘51a
Serine 2306˘285c 4315˘623b 4468˘913b 8875˘931a
Threonine 1490˘95b 2258˘192ab 2954˘444a 3887˘510a
Tyrosine 209˘24 186˘26 357˘84 515˘60
Valine 1193˘260b 1563˘30ab 2797˘502a 5584˘259a
Essentialaminoacidsc 6616˘145b 6992˘68b 12,878˘1472a 20,585˘983a
Total 15,749˘540c 21,189˘2108bc 24,424˘2837b 45,528˘2656a
Meanswithineachrowfollowedbydifferentlettersaresignificantlydifferent(p<0.05),one-wayANOVA,
randomized complete block design, df = 3,12; a Cystine was detectable but not found in the samples;
bW,wellwatered;D,droughtstressed;cComprisedofarginine,histidine,isoleucine,leucine,lysine,methionine,
phenylalanine,threonine,andvaline.
Inregionsofrelativelylowrainfallandinregionsthatexperienceperiodsofdrought,sugarcane
should be adequately irrigated to avoid exacerbating E. loftini infestations [14,66,69,70,94,95]. The
eldana borer, Eldana saccharina Walker (Pyralidae), a stalk boring lepidopteran pest of sugarcane
and other gramineous crops in Africa [96–99], responds to some environmental stimuli much like
E.loftini[14]. Droughtstress,forexample,isassociatedwithsevereE.saccharinainfestations[99–102]
andE.saccharinanumbershavebeenreportedtodecreaseinresponsetorainfall[103]. Larvalgrowth
ofE.saccharinaismorerapidandmorerobustinwaterdeficitstressedsugarcanethaninwell-watered
plants. Hence, African sugarcane growers are advised to keep their sugarcane fields adequately
irrigated[100,104,105].
3.2. SoilNitrogen
Nutrient-poorsoilsareasourceofplantstresswhichisoftenamelioratedbyapplyingfertilizers.
Relatively high soil nitrogen concentrations in forms that are assimilated by plants can augment
the nutritional value of species that host chewing and sucking herbivorous arthropods [106–110].
In this way, rich or excessive soil nutritional quality can exert stress by increasing the intensity of
pestinfestation. Highsoilnitrogen, forexample, affectsthedegreetowhichsugarcaneisinfested
andinjuredbyE.loftini[93]. InfieldplotslocatedintheLowerRioGrandeValley, organicmatter
with1.1%N(3320ppmnitrate)appliedatrelativelylowandhighrates8mobeforeplantingresulted
in2.6-to4-foldmoresoilnitrateatplantingtimethannoncompostedsoil[93]. Therecommended
rate of nitrogen fertilizer for Lower Rio Grande Valley sugarcane was applied at the beginning of
twoconsecutivegrowingseasons. Sugarcaneleaftissuefromtheheavilycompostedplotscontained
substantiallymorenitrogenthanleaftissuefromlowcompostandnoncompostedcontrolplots[93].
Leaf tissue from plants grown on heavily composted soil during the first growing season had
significantly(p<0.05)morenitrogenthanleaftissuefromthecontrol[93]. Freearginine,histidine,
and lysine, and total free essential amino acids and total (includes nonessential) free amino acids
wereingreaterabundancesinleavesfromtheheavilycompostedplotsthaninleavesfromtheother
treatments [93]. Further, fructose was ě2.2- and ě1.7-fold more abundant in sugarcane grown on
Agronomy 2016, 6, 10  7 of 18 
Agronomy2016,6,10 7of18
Agronomy 2016, 6, 10  7 of 18 
heavily composted soil than on the other plots (glucose and sucrose concentrations were not affected) 
hheedaauvvriililynyg cc oothmmepp poolssattneetdd a ssnoodiill r ttahhtaaonno noo nng rttohhwee oointthhgee srre ppasllooottnsss ((,gg rlleuusccpooessceet iaavnneddly ss (uuFccirrgooussreee cc 2oo)nn [cc9ee3nn].tt rrNaattuiioomnnbsse wwrsee orreef  lnnaoortvt aaaflff fEeec.c ttleoefddti))n i 
dduuerrniintnrggy  tthhhoeel eppslla aannnttd aa nnadddu rralattt ooeoxonint  gghrrooolwewsii nningg  sssueeagasasoorncnassn,, reree ssstppaeelckctstii vvweelelyyre (( FF≥ii2gg.u3u‐rrfeeo 2l2d))  [[a99n33d]]..  ≥NN2uu‐fmmolbbdee rgrssr eooafft lleaarrr,vv raaells EEp.e. llcootffittviinneiliy , 
eennitntrr yyh ehhaoovlleielssy a acnnoddm aapddouusltltte edexx piittl ohhtoosl letehssa iinnn  sisnuu gtghaaerrc coaatnnheee srs ttpaalllkokstss w w(Feeirgreeu ě≥re22 ..333)‐- ff[oo9ll3dd] .aa Tnnhdde ě ≥e2n2‐-hffoaolnlddc gegdrre enaatuteetrrr,,i trrieeossnppaeelc cvttiiavvleuelleyy ,,o f 
iinns hhueegaaavvricillayyn cceoo pmmlappnootssstt eeinddc pprellooatstsse stth hpaarnno diinnu tcthhtieeo noot tohhfee rEr p.p llloooftttssin ((iFF aiiggduuurrleets 33 w)) [[h99i33c]]h..  TTcohhneet ereninbhhuaatnnecsc eetddo  ntnhuuett rrmiittiiaoognnnaaillt uvvdaaleluu oeef o otffh e 
ssuunggeaaxrrctc aganneene peprlalaantnitostnsi  niancnrcderae tashesese sap mrporodouudncutt ciootifno inno fjuoEfr. yEl ot.f otloi tnfhtiiean dci ruaodlptus. lwTtshh weic ahhsicscoohnc citaroitnbioturntieb osuft toheost hsttoe p mtlhaaeng tmn viatuugldnneietrouafdbteihl ieotfyn  tethxoet E . 
gneelnoxfett rignaetini oeanrnaadtni odfnrt uhacnetdao msteho eu canomtnoocfeuninnttrj uaortfiy ointnojsu trhyseu tcgor gothepse.t scT rhotehpaa. stT shotehc ieaa stsisoouncgioaaftri,ho onws othfpi hclahon stto vpculcaulnnrets r vauibnlin lietryrealtabotiilEvit.eyll oytfo ti lnEoi.w   
alonfctdoinnfirc ueancnttordas etifocrnuosnc,tc omesneitg rhactot inobcnee snas turliamgtgiioetnisntsgs  tsnhuuagttgrtiehtsieotsns autlgh faaartc, twothrhe if cohsru otghcaecru ,p reswsithn i[cr9eh2l ]a. otAicvcletuhlyrosul ogiwnh  csrouenlgacaterinvcaetrnlayet  isoltonowso, ls 
mco(incglchuetmnbtpreasat oilofin mssti,at limknsgi)g nhgurt otbrwiet niao  innlia mtlhfieati cnhtgeoa rnvfuioltryr ticthoieomnppaelos tsfat[ec9dt2o ]pr. lAfootlrst h wtohueerg eph ecssoutm g[p9a2rric]s.a enAdel toshfto o1uo8gl%sh ( mcsluougrmea rpsctsaaonlkfes s stttaholakonsls )i n 
g(crtlouhwem noptishn eotrfh  tsertehaalektamsv)ei lgnyrtosc wodmunp riinons gtth etedh ehp felioartvssti lwgyr eocrowemicnopgmo sspeteraidsso epdnl,o otthfsa1 w8t %ienrcemr ceooarmseesp wtraialskse smdt hooafr en1 t8ihn%at nhm eooforfstehe sett rbaytlkr eisna ttthemnaensni fitinse d 
dthuEer. io nltoghfteitnrh ite‐rienfiadrtsumtcgeenrdot swin dijunurgryins [eg9a 3tsh]o.e nS f,tiartshlkta sgt riinonw cthrienea glso eswewa csaoosmnm,p tohorasett  tainhncadrn ecaoosfnefst wreotalb sp ymloiontsrt eew nthesriafien e1 od6f%fEs. ealtno bfdtyi n 3in1i-%tien ndhsueiafciveedide r, 
iEn.rj uleosrfyptien[c9i‐t3ii]nv.edSluytac, letkdhsa iinnn jiutnhr yeth l[eo9 w3h]i.gc Sohtm aclopkmso sipntoa tsnht dep llcooowtns t [cr9oo3lm]p. plootsst wanedre c1o6n%troaln pdlo3t1s% wheerea v1i6e%r, raensdp e3c1t%iv ehlye,atvhiaern, 
irnestpheechtiivgehlyc,o tmhapno sitnp thloet sh[i9g3h] .compost plots [93]. 
e 0.5
u Control
s
y leaf tissueg dry leaf tis00..4500..34 a a CLCHoihoCLHgwinohcihgt wk icrchcoeo ok cnlcmemo olnpmipmt otlopeipstsortotetssrtt a a
e/g drtose/0.30.2 b b b b b b
uctosg fruc0.2 b b b b b b
rm 0.1
f
g n
ma0.1
n Me 0.0
ea 2010 2011  
M 0.0
2010 2011
Figure 2. Mean (SE) mg/g dry weight of fructose found in leaves of sugarcane,  maize, and sorghum; 
FFiigdguuifrrfeeer 22e..n MMt leeeaattnne r((˘s SoSEvE)e) rmm bgga//rgsg  dwdryirty hwwineei egigahchth to otfy ffprfrueuc octotfo ssseue gfofaouru ninnddd iinicn alelteeaa vsveiegssn ooifff iscsuaugngata rdrcciaafnfneeer,,e mnmcaaeiizsz ee(,p, a a<nn 0dd. 0ss5oo)rr gg[9hh3uu]m.m  ;; 
ddiiffffeerreenntt lleetttteerrss oovveerr bbaarrss wwiitthhiinn eeaacchh ttyyppee ooff ssuuggaarr iinnddiiccaattee ssiiggnniifificcaanntt ddiiffffeerreenncceess( (pp< < 00..0055)) [[9933]].. 
30
a
Control
30
d 25 Chicken litter a
an no. larval entry and Mean no. larval entry anadult exit holes/stalk adult exit holes/stalk112205051120505 cCHCLcoiohgHLwnihcoit gk rccwcoheoo ln ccmcm oolpipmtmotoebpspsrototbsstt a a
Me 5 0 b b b
Larval entry holes b Adbult exbit holes
0
Larval entry holes Adult exit holes
FigFuigruer3e. 3M. Meaena(n˘ (S±ES)En) unmumbebresrso foEf .El.o fltoifntiinlia lravravlaeln etnrytryh ohloesleasn adndad audlutletx eitxihto hleosleisn isnu sguagrcaarcnaenset asltkaslks 
gFrigogrwuornwe on3n.  oMfinee flaidenl pd(±l oSptElso)at nsm uaemmnbedenerddse wodf i wtEh.i tlchohf ticichnkiie clnkaerlvnita tllei tret,neortrr, yloo rhw olol(ew1s0  a(21n,30d02 6,a3dk0u6g l/tk hgeax/h)itaa h)n oadlnehdsi  gihnhi gs(uh3 g0(6a3,r09c61a,6n91ek6 gs t/kaghlk/ahs)a ) 
agmraoomwuonnu tonsntos f foicefol dcmo ppmloopstots,s ata,nm adnenidnd ienndo n nwo-naitm‐ha mecnhedincedkdeedcno  clniottntreotrrl,o pol lrpo tlloso,tws2, 0 (2110101,21H,,3 i0Hd6ia dklgaglo/ghCoa o)C .a,onT.,d XT ;hXlie;g tlhtee trt(es3r0os6v ,o9ev1re6br a kbrgas/rhfsoa rf)o r 
eaamecahocuthyn pttyse pooeff  ochofo mhleoplioens ditn,i cdaaintcedat siein gs nnigiofinnci‐faaincmatnedtni fddfeiefrdfee ncreocennsctre(ops l(< pp 0l<o. 0t0s5.,0) 25[90) 31[9]1.3, ]H. idalgo Co., TX; letters over bars for 
each type of hole indicate significant differences (p < 0.05) [93]. 
In addition to being similarly affected by water deficit stressed sugarcane plants, E. saccharina 
Inadditiontobeingsimilarlyaffectedbywaterdeficitstressedsugarcaneplants,E.saccharina
inijunrjuyInrty oa tdsoud sgiutaigoracnar cntaoen ibene iiAnn fgAr ifscriaimciasil iaesrx elayxc aeacrfebferacbtteaedtdebd by byhy we haaevtaeyvru yds ueefsoiecf iotnf si nttrriotergsosegenedfn es rfuetigrltaiizrleiczraen[r1e 4[ 1p,14l0,a14n0,t14s1,,1 1E1].1. ]Ms.a Mcocdhoeadrreainrtaeat e 
ninintjuriotrrgyoe tgnoe nsfeu rfgetairlrtiiczlaieznreear  ipnapp Alpicflraiictcaiaot iniosn ies xirase crceeorcbmoammtemedn ebdnyed dheedian vinyS  ouSuosteuh othAf  nfAritifcrroaicgateo ntoa f veaorvtiidoliizdine rit ne[n1te4sni,1fsy0ifi4yn,1ign1gE1 ].E. sM.a csocadhccaehrriaanrtiaen a 
inniiftnerofsetgasettnaiot infoesnrts[i 1li[0z14e0,r14 1,a11p1]p1p]l iacparattiircotuincl uairslal yrrelycd oudmruimnrigenngpd eeprdeior diinosd Ssoo fuodtfh rd oAurofgruhigctah[ t1t o0[ 15a0]v.5o].iI dnI nia nrateeranesassiwf ywhinehgree rEeE.  .Esal.o ccfltohifantriininiis a is 
pinrpoferbsoltebamlteioamntiasct ii[cn1 i0sn4u s,g1ua1gr1ca]ar cnpaean,regti,rc oguwrloaewrrlsyer sshd souhuroilnduglad lp saoelrsaioop adppsly polnyfi  tndroirtgoroeugngehfnet  rft[ei1lri0tzi5le]irz. ejIurn dj uiacdrioiecuaioss luywsl[hy1e 4[r,19e43 ,]E9.3. ].l oftini is 
problematic in sugarcane, growers should also apply nitrogen fertilizer judiciously [14,93].
Agronomy2016,6,10 8of18
4. BioticEnvironmentalStressFactors
4.1. WeedGrowth
WeAegdrongormoy w201th6, 6e, x10e rtsavarietyofeffectsontheecologyofsugarcanefields[94],them8o osf t18o bvious
beingcompetitionwiththecrop. Infestationsbyweeds,especiallyperennialslikejohnsongrass,can
4. Biotic Environmental Stress Factors 
causesubstantialeconomiclosses[112–114]ofupto84%[115].Weedscompetemoreeffectivelyagainst
sugarca4n.e1. tWhaeend mGraowntyh short-seasonrowcropstoanextentbecauseofsugarcane’srelativelywiderow
spacing(«1W.8eemd )garonwdths leoxwertss ea evdarliientgy ogfr eoffwectths o[n1 1th6e] .ecLoelosgsyc oofm supgeartcitainvee fiaenldns u[9a4l],w theee mdosspt oebcvieiosuds ieback
whenthbeeisnugg caormcpaenteiticoann woipthy thcleo csreosp.o Ivnefershtaetaiodns[ 2b2y, 1w1e7e]d,sb, uestpuecnicalolyn tpreorlelnendiaalsn lnikuea jlohsnusmonmgrearssw, ceaend shave
beenasscoacuisaet esudbwstaitnhtiarel decuocntoiomnisc ilnosssuesg [a1r1c2a–n1e14s]t aolfk udpe tnos 8it4y%,b [i1o1m5].a sWs,eeadnsd ccoommpemtee rmcioarle seuffgeacrtivperloyd  uction
against sugarcane than many short‐season row crops to an extent because of sugarcane’s relatively 
of up to 24%, 19%, and 15%, respectively [22]. While weeds are clearly stress factors under many
wide row spacing (≈1.8 m) and slow seedling growth [116]. Less competitive annual weed species die 
circumstances,inwetenvironments(e.g.,southernLouisiana)theyarenotaslikelytocreateconditions
back when the sugarcane canopy closes overhead [22,117], but uncontrolled annual summer weeds 
ofwaterhadveefi bceitenst raesssosciinatesdu gwairthca rneedu[9ct4io]nass itnh esuygaarrceatnoe csotamlkp deetensfiotyr, sbuionmliagshs,t adnudr icnogmtmheerceiaarl lsyugpaarr tofthe
growingprsoedauscotino.n Aoff utepr toth 2e4%su, 1g9a%r,c aannde 1c5%an, roepspyecctliovseelys ,[2e2x].c Wluhdilien wgeeendos uargeh clesaurnlyl isgtrhetsst ofacktiolrlsa unnnduera lweed
undergrmowantyh c,itrhcuemdsetnansceems, iant wofetd ernyvvireognemteantitos n(eb.ge.,c soomutehseran mLouulicshiatnhaa) tthceoyn asreer vnoets asso liilkmelyo itsot ucrreeat(el owfree
conditions of water deficit stress in sugarcane [94] as they are to compete for sunlight during the early 
prolinelevelsinthesugarcaneindicateabsenceofwaterdeficitstress[118])[119]. InthedrierLower
part of the growing season. After the sugarcane canopy closes, excluding enough sunlight to kill 
RioGrandeValley,weedsmightcompleteforwateraswellasforspaceandlightwhenthesugarcane
annual weed undergrowth, the dense mat of dry vegetation becomes a mulch that conserves soil 
isyoung. ItispossiblethatweedsaremorelikelytoaffectsugarcanephysiochemistryinsouthTexas
moisture (low free proline levels in the sugarcane indicate absence of water deficit stress [118]) [119]. In 
inwaysththe adtriienrc Lreoawseer iRnifoe sGtraatniodne VbayllEey.,l owfteiendist mhaignhitn cowmeptlteetre efonrv wiraotnerm ase nwtesl.l as for space and light 
Whwilheenm tahney swugeaercdansep eisc ieysouanrge. aIltt eirsn paotessihboles ttshtaot pwheeydtos pahrea gmoourse nliekmelya totod easffe[c1t1 9su],gparactahnoe gensof
sugarcapnheys[i9o4c]h,eamnisdtryD .ins ascocuhtahr aTliesxaasn idn Ew.alyosf titnhiat[ 1in4c],rewaseee idnsfehstaatvioena lbsyo Eb. eleonftinsih othwann itno wfaecttielirt ate the
environments. 
reductionofdamageinflictedbyD.saccharalis(Figure4)[120–122]. Predationcanbeadecisivefactor
While many weed species are alternate hosts to phytophagous nematodes [119], pathogens of 
againstD.saccharalis,particularlyinwetormoistregionswhereredimportedfireant,Solenopsisinvicta
sugarcane [94], and D. saccharalis and E. loftini [14], weeds have also been shown to facilitate the 
Buren, populationsflourish[22,123]. Usingstable-activablerareearthelementsastracerstomark
reduction of damage inflicted by D. saccharalis (Figure 4) [120–122]. Predation can be a decisive factor 
(presumaagbailnystm Do. nsoacgcyhanreal)isS, .pianrvtiiccutlaarcloyl oinn wieest, oSrh omwoilset rreegtiaoln.s[ 1w2h2e]rde erteedr mimipnoerdtetdh fairtet hanetd, Sisoclerneotpesifso raging
territoriiensvi[c1t2a 0B]uarreen,s puobpsutalantitoianlsl yflosumriaslhl e[r22i,n12w3]e. eUdsyinsgu sgtaabrlcea‐ancetipvalobltes ,rpareer meairttthi neglemdeenntsse arsc torlaocnerisz atot ionand
thatresumlaterkd (ipnre6s0u%malbelsys mDo.nsoagcycnhea)r aSl.i sinivnicjutar ycotloonsieusg, aSrhcoawnleers etta lakl. s[1t2h2a]n dientersmuginaerdc athnaet fitheel ddipsclroettse devoid
foraging territories [120] are substantially smaller in weedy sugarcane plots, permitting denser 
ofweedgrowth. Intermsofthenaturalenemycomplex,Louisianasugarcanefieldsinfestedwith
colonization and that resulted in 60% less D. saccharalis injury to sugarcane stalks than in sugarcane 
monocot,dicot,andamixofbothweremorediverseintermsofsoilsurface-andfoliage-associated
field plots devoid of weed growth. In terms of the natural enemy complex, Louisiana sugarcane fields 
arthropiondfess,teidn cwluithd imngonnocaottu, rdailcoet,n aenmd iae smoixf oDf .bsoathcc whaerrael ims,orteh adnivebraser ein-s oteirlmssy osft esmoils s[u1r1fa7c]e.‐ aSnudg arcane
systemsfoilniaLgeo‐uasissoicainataeds uarpthprooprtoděs8, i4ncslpuedciniegs noatfusrapli edneerms,ieism opf Do.r tsaacnchtaeraglgis, pthraend baatorer‐ssooilf sDys.tesmacsc [h1a1r7a].l is[124],
in18famSuigliaersca[n1e2 5s]ysatnemdss pinid Leorudisiivaneras istuyppaonrdt a≥8b4u nspdeacniecse osfa srpeidinercsr,e aimsepdorbtayntw eegegd pgrerodawtotrhs ionf sDu.g arcane
saccharalis [124], in 18 families [125] and spider diversity and abundances are increased by weed 
fields [22,126–128]. Anthocorids, nabids, reduviids, earwigs, carabids, various wasps, and other
growth in sugarcane fields [22,126–128]. Anthocorids, nabids, reduviids, earwigs, carabids, various 
naturalenemiesofD.saccharalishavealsobeenreportedtobemorenumerousinweedysugarcane
wasps, and other natural enemies of D. saccharalis have also been reported to be more numerous in 
habitatsthanwhereweedshavebeeneliminated[22,121].
weedy sugarcane habitats than where weeds have been eliminated [22,121]. 
50
Treatments
s
e Weedy sugarcane field plots
od 40 Weedless sugarcane field plots a
n
e a
nt
d i 30
e
r
o
b
ge 20 b b
a
nt
ce 10
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e
P
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1985 1986
Year

Figure4F.igMureea 4n. M(˘eSanE ()±p SeEr)c peenrtcaegnteasgoesf osfu sguagracracannee iinntteerrnnooddees sbobroedre bdy bDyiaDtraiaeat rsaaeccahsaaraclcihs ainr awlieseidny wanede dyand
weedless sugarcane field plots at harvest during two growing seasons, Assumption Parish, Louisiana; 
weedlesssugarcanefieldplotsatharvestduringtwogrowingseasons,AssumptionParish,Louisiana;
significant (p < 0.05) differences are indicated by different letters over the bars [22]. 
significant(p<0.05)differencesareindicatedbydifferentlettersoverthebars[22].
Agronomy2016,6,10 9of18
Conservationofweedsalongfieldbordershasbeensuggestedformaintainingpopulationsofa
parasitictachinidfly,Lixophagasphenopheri(Villen.),whichattackstheNewGuineasugarcaneweevil,
RhabdoscelusobscurusBoisd.,inHawaii[129]. Becauseuncontrolledweedgrowthisoftendeleterious,
limitedweedhabitat“islands”withinsugarcanefields[117]orconfiningweedstofurrowswithearly
seasonweedcontrolonlyontherowtopsmightbewaysofconservingS.invicta,spiders,andother
arthropodsthatparasitizeandconsumeD.saccharalis[22].
ApreliminaryreportsuggeststhatS.invictamightpreyonE.loftini[130],hence,vegetational
diversification using weeds might enhance populations and diversity of natural enemies [14,53],
reducinginjurymuchinthesamewayasS.invictacanforD.saccharalis. InthedryLowerRioGrande
Valley, however, rankweedgrowthincottondidnotresultinelevatednumbersofS.invicta[131]
whichreacheshigherdensitiesinwetterregionssuchassouthernLouisiana[123]. Therefore,inthe
LowerRioGrandeValley,weedconservationwiththeaimofincreasingnaturalenemypopulations
mightnotbeparticularlyeffective.
4.2. GreenchopLeafResidue
Thecommonpracticeofburningtheleavesoffthestalksofsugarcanejustbeforeharvestpollutes
theair,resultsinadversehealtheffects[132–134],andcancausedeteriorationofsoilstructureand
lossoforganicmatterandnutrients[135,136]. Sometimestheleavesareinsteadstrippedfromthe
stalks, often cut into small pieces and left as a 15–20-metric ton/ha mat of “greenchop” covering
thesoilsurface[137]8–10cmdeep[37,138]. Whilegreenchopmulchhasbeenreportedtoimprove
sugarcaneyield[139–143],itcanalsoimmobilizeNandP[144,145],inhibituptakeofsoilNunder
certainconditions[146,147],and,presumablybecauseoftheinducedstress,reducetillering[148]and
yield[149]. PlantingseasonsugarcanestalksharvestedintheLowerRioGrandeValleyhad2.3-and
2.8-foldmoreE.loftinientryholesperstalkinfieldplotswheregreenchopwasleftonthesoilsurface
asamulchandwheregreenchopwasmechanicallyincorporated20cmintothesoil,respectively,than
inplotswithoutgreenchop[150]. Duringthesamegrowingseason,percentagesofE.loftini-injured
internodesperstalkwere2.3-and2.6-foldhigherinplotswithgreenchopmulchandsoil-incorporated
greenchop,respectively. Statisticallysignificanteffectsofgreenchop,however,didnotoccurduring
theratoonseason[150]. Althoughgreenchopcaninducestresstosugarcanebyinterferingwithsoil
nutrientavailability,thedifferenceinE.loftinidamagedinternodesdidnotoccurasaresultofelevated
nitrogenandfreeaminoacids. Itispossiblethatthegreenchop,whichdriesinthefield,itselfattracted
E.loftini.
4.3. ProximitytoSusceptibleMaize
CropsthatarevulnerabletoE.loftinicanserveasreservoirsforthepestwhich,onmovingintothe
sugarcane,intensifiesstresstotheplantsfromlarvaealreadytunnelingwithinstalks. Wheresugarcane
and maize are grown (along with other crops) as a patchwork agricultural landscape, such as the
LowerRioGrandeValley,E.loftini-susceptiblemaize,preferredoversugarcane[51,52],canaccumulate
thepestuntilthemaizeisharvestedandtheadultsmoveintosugarcane[52]. Threemonthsafter
AugustharvestofmaizeintheLowerRioGrandeValley,larvalentryholesinNovember-harvested
sugarcanestalks(sugarcaneinsouthTexasisusuallyharvestedNovember–December)hadincreased
by7-to8-fold(Figure5)[52]. TacticsthatmighthelptoreducemovementofE.loftinifromharvested
maizeintosugarcaneincludegrowingE.loftini-resistantmaizecultivarsnearsugarcaneandavoiding
E.loftinisusceptiblemaizecultivars[52].
TwotransgenicBtmaizevarieties(registeredforuseagainstanumberoflepidopterouspests
but not E. loftini, Table 3) were demonstrated to exhibit resistance against E. loftini injury in the
LowerRioGrandeValleycomparedwithtwomaizecultivarslackingresistancetolepidopteranpests
(Table3)[151]. Oneofthetworesistantcultivars,Pioneer31G71,decreasedlossesofentirestalksfrom
lodgingandfungalrotby60%andreducednumbersoflarvalentryholesby41%[151]. Theother
resistantcultivar,GoldenAcres28V81,reducedstalklossby94.6%andentryholesby>99%[151].
Agronomy2016,6,10 10of18
NumbersoflarvalentryholesinPioneer31G71werenotstatisticallylowerthaninnon-Btcontrol
Agronomy 2016, 6, 10  10 of 18 
cultivars [151], and because the cultivar was associated with a <70% decline in adult emergence,
iteisffneocttivaen tortaapb lcyroepff efocrti vsueptprarpescsrinopg Efo. rlosfutipnpi rinesjusirnyg toE .nleoaftribnyi isnujugrayrctaonne e(aTrabbyles u3)g. aOrcna nGeo(ldTaebnl eA4c)r.es 
On28GVo8l1d estnalAkcsr, ehso2w8eVv8e1r,s ntaol kasd,uhlot wexeivt ehro,lneos awdeurlet oebxsitehrvoeleds [w15e1r]e. Aobns eidrveaeld d[e1a5d1] e.nAdn tirdaepa cludletiavdare nfodr a 
trasptaclku lbtiovrairnfgo rpaesstt awlkillb obrei nmgoprees tatwtriallcbtievem tohraena tsturasccteipvteibthlea ncuslutisvcaeprst,i balnedc uslttaivlkasr sw,ailnl dbest alelksss wpriollnbee to 
lessshpatrtoenrientgo, slohdatgtienrgin, ga,nldod sgtainlkg ,roant ddissteaalskerso, tedxtiesenadsiensg, ethxteeinr dcainpgacthiteyi rtoc acpoanctiitnyuteo tcroapntpininuge tthraropupginhg its 
thgrorouwghinigts sgeraoswonin [1g4s]e washoinle [c1u4r]twailhinilge acudrutlati elimngeragdeunlctee tmo ethrgee enxcteentot atchheieevxetedn btya cGhoieldveend AbycrGeso 2ld8Ven81. 
AcIrne sth2e8 sVa8m1.e Ivnetinh,e as aBmt Cervye1iAn,ba mBatiCzery c1uAltbivmara tihzeatc dueltcirveaarsethda studrevcirveaals oefd Ds.u sravcicvhaalraolfisD t.os nacecahralyra zliesro 
townaesa rslyugzgeersotewda stos ubgeg ae sttreadp tocrboep afotrr atphactr oppesfot r[1th12a]t. pGeostld[1e1n2 A].cGreosl d2e8nVA81c rwesas2 8aVlm81oswt acsoamlmploestetly 
cormespisletatenlty troe silsatravnatl toE.l alrovftailnEi .bloofrtiinngi b(oTrainbgle (T3a) b[l1e541)].[ 1W51h].itWishh itliasrhvlaalr vfeaeldfeinegd in“gtra“ctrkasc”k ss”casrcraerdre dthe 
thoeuotuetremrmosots ttitsissusue eoof fGGooldldeenn AAccrreess 2288VV8811 wwiitthhoouutt ppeenneettrraattiinngg tthhees statalklk,,s usuggggesetsitningga natnibtiiboisoissias satsh tehe 
babsaissiosf orfe sriesstiasntacnec[e1 5[115].1H]. eHnecnec,eG, oGldolednenA cArecrse2s8 2V88V18i1s ias pao pteontetniatlilayllsyu siutaibtalbelter atrpapp lpanlatnfto froEr .Elo. fltoinftiini 
egeggsgws iwthithn engeliggliibglieblrei srkistko ttoh ethset asltkal[k1 5[115].1]G. rGorwoiwnignga tar atnrasngsegneincimc maizaeizve avraiertiyetlyi kleikGe oGldolednenA cArecsres 
282V88V18w1 iwthithhi ghhigbhi obcioidciadlaalc aticvtiitvyitayg aaginasintsEt. Elo. fltoinftiinwi iwthiitnhiang arigcruicltuulrtualralal nladnsdcascpaepseisn tienrtmerimnginlegdlewd iwthith 
susguagracarcnaenfie eflidelsdms mighigthbt ebteh tehbe ebsetswt awyayo fo“fd “edpelpoyloinyign”g”m maizaeizea saas da edaedaden edndtr atrpapcr ocrpopto top rporteoctetct 
susguagracarcnaen.eF. oFromr manaynyy eyaerasrist iht ahsabs ebeenenre rceocmommmenedneddedth tahtagt rgorwoweresrps lpanlatnstu sguagracracnaenaes afsa rfaarw aawyaays as 
popsosisbslieblfero fmromm amizaei,zbe,u btutht ethreo rleoloef otrf atrnasngsegneicnsicisn isnt asltkalbko broerremr manaangaegmeemnetnmt imghigthcth cahnagnegteh athtaptr pacraticctei.ce. 
ReRseisstiasntacnecme amnaangaegmeemnet,nht,o hwoewveevr,ecro, ucoldulrde mreaminaiann ainss iusesu[1e 5[21]5.2]. 
s
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FigFuigruer5e. M5. eManea(n˘ S(±E )SnEu) mnubmerbseorfs Eo.fl oEft. ilnoiftlianriv laalrevnatlr yenhtoryle shoinlems ainiz me,asiozreg, hsuomrg,haunmd,s aungdar csuangearocnanthee on 
hatrhvee shtadravteesfto rdmataei zfoera nmdasizoerg ahnudm s(oinrgAhuugmu s(ti)na nAduignussut)g aarncda nien osnutghaerchaanrve eostni ttshde ahtear(ivneNst oivtse mdabteer )(,in 
fieNldopvleomtabsesra),y ,fHieildda plglootC aos.s,aTyX, ,HUiSdAa;lgdoif fCeroe.,n tTlXet, teUrSsAov; edrifbfaerrsenwt itlhetinteersa cohvyeer abrainrsd iwcaittehisnig enaifichca ynetar 
dififnedreicnactees s(ipgn<if0i.c0a5n)t[ d52if]f.erences (p < 0.05) [52]. 
TaTbalebl2e. 2B.t Bmt amizaeizvea vriaertiieetsieasn adntdh ethpee pstessatsg aaginasitnwst hwichhicthh ethyeayr earree griesgteisrteedre[d15 [11]5.1]. 
  PestPsests   
VVaraireiteytya nanddA accttiivveeG geennee  ComCmoomnmNoanm neame  ScientSificiceNntaifmice name 
Pioneer 31G71  blacbklcaucktw courtmworm  AgrotiAsgiprsoitliosn ipHsiulofnn aHgeulfnagel 
cornearworma Heliothiszea(Boddie)
HX1 gene  corn earworma  Heliothis zea (Boddie) 
Europeancornborer OstrinianubilalisHübner
faElluarormpeyawno cromrn borer  SpodopterOasfrtruigniipae nrduabiJl.aEl.isS Hmüitbhner 
Pioneer31G71
lessercornstalkborer Elasmopalpuslignosellus(Zeller)
HX1gene fall armyworm  Spodoptera frugiperda J.E. Smith 
southerncornstalkborer Diatraeacrambidioides(Grote)
southlwesessetre rcnorcno rsntablko rbeorrer  DiaEtrlaasemagopraanlpduioss leilglnaoDseylalurs (Zeller) 
sugarcaneborer Diatraeasaccharalis(F.)
southern corn stalk borer  Diatraea crambidioides (Grote) 
westernbeancutworm LoxagrotisalbicostaSmith
southwestern corn borer  Diatraea grandiosella Dyar 
sugarcane borer  Diatraea saccharalis (F.) 
western bean cutworm  Loxagrotis albicosta Smith