:~~;"..

~',rl

.~

",~: -, .:~I oj

l"':~

,:: August 1990 FIR~

;t,!.'f: the largest larva is T

-~ --'.-::-;,,:-. -';":ra?:" -- - liT." ;-~~'--, that examine

" - - . I of reslstar~- - accurate when

.~, tightly co~"! ::::: ,. Ther.e£ore. lab.

MICHAEL J. FIRKO. AND JANE LESLIE HA y~

Southern Field Crop Insect Management Laboratory, USDA-ARS,Stoneville, MiSliSlippi 38776" .

on size variatioIJ the resolution (: this end, we q

relationshil. weight

!. Materia!i ... We collected H. vi

;; ber 1987 from a 950~ (three cotton varietie. Leland, Washington C

t randomly collected fr,:: field. Larvae were re"~.. containing about 15 J

t Hartley 19&5) contain~ 6; Hartley 1987). Of;~~ survived to the pupal:~,; oratory colony. Initial.~ ed in 4-liter card boar~ females in each at 25t": a photoperiod of 14:1(J!'; which were designed: netic diversity in the

; among generations. r... were used at all time~. each container 3-4 tin~ died, and larvae from'5': ed among the breedin,$ ~~ surviving to the adult'" ~ opment time) were pr

"and given the opportl,f- quent generations. Co:11.:' 3-5 generations with

~: 200,543, 1,1&5, and 1,(: virgin adults were coil. determined, and they

in 0.5-litcr cardboardperimental cohort. Rei,

-: minimized by pairin~;. ferent sul>colonies. N<,~ vae, and not alllar";ll'~ 54 m31t.'s product.od th.

, pt.'rimt'nt...- Each I:lrva \\'as \,'('i

:' no morc tl13n 1 h bt'fowith t"itht'r 0.1 or 1.0 j.gr:lde; f.\fC Carpor3t!

': tonl.' (31131ytic31 graul.)," originOiI uit.'t cups ,,'her

dit'u ur pupated, Largo~ fur 1.0-"1; trt'3tmC'nts.

'I ['II

.I

.t

VARIOUS MODELS have been proposed to predict

change in POpulations folJowing insecticide appli-

cation (Plapp et al. 1979, Taylor 1983, Georghiou& Taylor 1986, Uyenoyama 1986, Via 1986, Roush& McKenzie 1987). Resistance to any particularinsecticide depends not only on resistance allelesthat an individual POSsesses but also on a varietyof nonheritable genetic and environmental facton

- that affect the expression of resistance (Taylor 1983).

Thus, the accuracy of models designed to predictgenetic change depends not only on how accurately

, genetic factors have been de6ned but also on theextent to which epigenetic facton affecting genetic

'expression of resistance are considered., Because expression of resistance is affected bymultiple genetic and epigenetic factors, individualswithin populations do not fall into discrete cate-gories. Instead they show continuous tolerancevariation (Finney 1971). The term tolerance issometimes associated with low-level resistance, butwe use tolcrance In its original sense to refer to acontinuous measure (Finney 1971) of Icss-than-complc:tc rcsistalice (CLoorghiou 1972). For con-venien(."t', resistOince to illsecti<:iucs has lH-ocn typi-cally trc.':ltcu :IS a (.'at('gurical tr:lit (i,e., SU5(.'('ptihle

-Thi;-;:;;;--;;pr",. II.. ,rsull. of ,;;;-;~~i;"".\i;;;;:;;;-;;;-;PO'OfKiru,y "'oo~ ow pt'sIICNJe.J.., In consl,Iul~ an ..ndur-RIeIII or a '~Int'rK1lIIOfI I", ,I. use by L'~D,\ no, do.-s II "nply"'lj"r~linn und.., F""R.\ OJ, ~'"..rKJ..,10 Curr..nl all,lr l'~D\-\II'-~\Jt'., \\'nl..m. T.., 7\5'.)6

'Curr..nl add,f'Uc l'SD.\-.~, ~"F.s, /',n.-,.'I... La 713110

22:1FIRKO 61 H.'YES: LARVAL WEICIIT AND RESISTANCE IN TOBACCO 8UD\VORM~ugust 1990

the larg~t larva is jj':; hl';lvit"r than the smallest.AltlKlugh ,,'c.'ight ranges of this Inasnituuc may betypical of variation in fielll populatiollS. laboratorystudies thl1t examine particular factors affectingexpression nf resistance (e.g.. genetic factors) arecPost accurate when factors such as larval weightare either tightly controlled or precisely consid-

. ered. Therefore. laboratory-derived relationshipsbetween tolerance and weight can be coupled with

': data on size variation in wild populations to im-, prove the resolution of resistance predictions. To-

:' ward this end, we quantified larval tolerance to.. cypermethrin in laboratory-reared H. vireacens and';' examined relationships between tolerance and lar-.: val weight.

Table I. ScottrinA C'rit..ria

..\bilityto

rightitselr

Activity and ca~bilitiesScOft'

01I".5

e789

10

NoNoNoNoNoNo

NoYesYesYesYes

NoneMi- activity after persistent p~ngMinor activity, immediate resp)n5eSlight independent activity, responsiveActive, slow writhing. no controlAmve. vigorous writhing. no auempts to right

itselfAmve. attempts to right itselfActive, rights itself with difficultyActive, rights itself easily, but adverse effectsActive. rights itself easily, mi~ effects onlyAmve, no visible effecU

Eadt indivkluallarva was aulgned a -- from 0 to 10 at each~ <- text).

criminate against larvae in specific weight classes.larvae showing evidence of an impending or recentmolt were not used.

Beginning 0.5 h after treatment, we observedeach larva when it was agitated gently with a bluntprobe; upright larvae were rolled onto their backs.Responsiveness, activity level. type of activity, andability of the larva to right itself were the criteriafor scoring tolerance as a continuous trait. Elevenlevels of adverse response (0-10) ,vere distin-guished (Table 1). In other studies, individuals thatwere scored from 0 to 6 on our scale would havebeen considered dead (Roush & Wolfenbarger 1985,Luttrell et al. 1987, Hoy et al. 1988). We observedand scored each individual at 0.5, 1. 2. 4, 8, 24. 48.72, 96, and 120 h after treatment. Data from con-secutive observations were summed to providevariables for analysis that represented cumulativescores through times (T) 24, 48, 72, 96, and 120 h(variables T24h. T48h, T72h. T96h, and TI20h).Individual observations were not independent (e.g..once an individual died all subsequent scores were0). but this continuous measure of tolerance incor-porated degree of debilitation at numerous inter-vals and total survival time. SAS (SAS Institute.l985)was used for analysis of variance and regressionprocedur5.

:5t6.I)Sps,...,

Iyos.

1'5CO,1-if-er:2)

~~e-'1.\er-iereIe"e-Isl'

Results

Larval tolerance to cypermethrin in H, vlrt'scenswas expressed as a continuous trait at both doses(Fig- 1 and 2)- The shapes of thc freq\lellcy his-tograms of tolerance phenotypes ,,-ert! similar tothose describcd by Fillll!.'}' (19,1) for tolt'r:lllc!.' (>ht'.lIolypeS- Hislogram sllapt. tlt'I>t.'lltll'tll,arlly 1111 lilt'IIlIucrlyillg uisiriulilioll of loarv.aI \vl'i~llls 1II,Il \V.I~approximalt'ly \lIIifurlll- ~1;lIIY l'lr\";lt' l~).O-I,~".1III~) Ireall..cJ \villl 01 jig (.'YI)('rllll1hrili ~lIrvi\t'(lSlIIIIC illuiviullOJls Ih:ll r:Ulllal 11.IVt' 1)('l'lIl-I.I~~ilit'tl .1..alt'OJJ OJf It'r 24 h SlIbSl'tl"elllly rt'l'(lvl'rl,J. 1"III,tlt-tl.l'lIIcrgl..J ;as :ltlulls, OIIIJ rl'l)rlllllll-t'll- St)llIl' illtliviJ.

~ Materials and :\Iethods

We collected H, virescens eggs during Septem-ber 1987 from a 95G-acre (~380 ha) cotton field(three cotton varieties) immediately southeast ofLeland, Washington County, Mississippi. Eggs wererandomly collected from 5 plots (8 ha) within thefield, Larvae were reared in plastic cups (22,S ml)containing about 15 ml of artificial diet (King &Hartley 1985) containing a mold inhibitor (Powell& Hartley 1987). Of the field-collected eggs. 219survived to the pupal stage and founded the lab-oratory colony. Initially, pupae emerged and mat-ed in 4-liter cardboard cartons (25 males and 2.5females in each at 25 :t 2-(;, 60 :t 10% RH, anda photoperiod of 14:10 (L:DJ). Rearing techniques.which were designed specifically to maintain ge-netic diversity in the colony, resulted in overlapamong generations. Multiple breeding chamberswere used at aU times. Eggs were collected fromeach container 3-4 times each week until all adultsdied, and larvae from each collection were includ-ed among the breeding population, All individuals

, surviving to the adult stage (regardless of devel-, opment time) were provided with potential mates. and given the opportunity to contribute to subse-~ quent generations, Colony size was increased over.:: 3-5 generations with approximate cohort sizes of

.:", 200, 543. 1,185, and 1,699. Beginning in April 1988.-, virgin adults were collected daily, their sexes were:' determined, and they were mated as single pairs

in O.5-liter cardboard cartons to produce the ex-..;;, peri mental cohort. Relatedness between parents was.: minimized by pairing males and females from dif-

ferent subcolonies, Not all pairings produced lar-vae, and not all larvae were used; 158 females and54 males produced the 416 larvae used in this ex-

perilncllt.Eat:h 100rvii '''as wei~hcd to the neare5t a,1 mgnu IIIllrc thOln I II ht.'rorc topicOlI treatment (1,0 Ill)','ilh t:itllt.'r 0.1 or 1,0,.g cYI>C.'rmelhrili (tet:hllical-groldc'; I:~I(: Ulrl)(lrOltioll, l'rill("eloll. ~,J,) in ace-till It' (OIIIOIlytic;J1 ~raclc') Llr"Ole "'t.'re trt.'iltl-c.J illllWlrurigillOiI Uil't culls ,,'III'rt' tllt'Y rrffiililll'li ulltil theydic.'tl fir pul~Ic.'d. l,oIrgt.' lilr\oIl' "c're 1101 :I"Olil:lI)lt,{or I,U'Il); trr3tllll'III\. ,-\llllcllI~1a "~ JiJ lICIt Ui5-

~'.;r

.~ ,

...~.,..

~wi:~:.

~~~~:. . .~:,'

f~:-.". ,;--'~'.~..-.' ~.

~ .~~.~:..

. --:. ... '- .-

*...

1224J()t'JI~AJ. ()J.' ECO~OMI(: E~TO~IOLOG\'

Yr)'. ~'1. I\r). ..\ul:ust 1990 FIRKO 61 HA ,.

...

10

T0 60LER 50ANC 40E

.~..uz..~ 20'0

~

)0'

..uzw~20(7w

~ *so

..1

. .,. ,. 22 . JO ,. » ~ .. 50 ,. 58 Ii (

~nRI-

u .. ., .. '7 .. .t 20 ,. 22 a ,. a a 27

~n8ImFiS. 1. Frequency histogram of cumulative toler-

ance scores of H. viresccn8 larvae. dose - 1.0 JIg cyper-

methrin per larva. Larvae weighed 9.4-36.1 mg. Vari-

able. T72h (sum of tolerance Scores through 72 h. seetext); n = 173. ..

30

T~ 208H

10

200

Fig. 3. Plot of tolerance verStlarvae weighing 9.0-1i5.4 mg. nweight was linear. Least-squares I

Discussion

With topical application ofthat individuals in particular trceive and the actual amount 01iog detoxification vary slightly

30T 280L 26ER 24AN 22CE 20

uals probably survived because of their size alone.At larval weights < 100 mg, the relationship be-tween tolerance and weight \vas linear, with \veightvariation accounting for 55% of observed tolerancevariation (Fig. 3). Tolerance values reached an as-ymptote near l00-mg larval \veight. The l00-mgcutoff is probably dose-specific; based on our re-sults, \ve expect the asymptote to OCcur at heavierweights for higher doses. Tolerance scores of somelarge larvae approached the maximum possiblevalue. Only 5 of 31 larvae> 100 mg died beforereaching pupation (86% survival).

Most larvae (9.4-36.1 mg) treated \vith 1.0 JIgcypermethrin \vere totally debilitated within 24 h,none survived to pupation, and none showed evi-dence of \veight gain following treatment. The\veight range of these larvae is greater than thatusually used for He/iothis studies, but the resultscan be put into familiar perspective. No larvaescored higher than 4 at the 48-h observation, in-dicatillg that 1.0 JIg per larva corresponds with atleast a 48-h LO.. for this population. Table 2 showsfrequency distributions of tolerance scores at par-ticular observation times (24-, 48-, and 72-h ob-ser~'ations, noncumulative). Tables 1 and 2 can beused to generate LO, values for a variety of fatalsymptoms.

Among larvae treated with 1.0 JIg cypermethrin,\,'eight variation accounted for 11 ~ of the observedtolerance variation (Fig. 4). Less tolerance varia-tion \vas e-xplained by \veight variation at 1.0 JAgrelative to 0.1 JAg (Fig. 3) largely because a smallerweight range was examined (26.7 versus 91.0 mg).Genetic variation among individuals explainedmuch of the observed tolerance variation and willbe reported separatcly (M.l.F. & l.L.H., unpub-lished data); consequently, the amount of variationexplained by \ve-ight de-pendffi on the size of weightrange examincd. Over Vf'ry narrow weight ranges,weight variation explained oilly a sm:lll portion ofobS(.'rved tolerall<:c: vari:ltioll and ()tlll'r {(\<:tors pre-domillatt'd, Ilo\\"c'\'c'r. p\'pn CI\'pr a I (J-ln~ \\'pightrange typically uspcl {or pyrcthr<lid to\icity stlltlies

18No. larvae per observation period

Score24 h 48 h 72 h

01!3456

12

I:i~. I. rh.1 ,.f 1..I,.r,,"\-.. ,,'r'I..r"..' ",'i~1111I1; ~)..-;>u I m~. II

.\ugust 1990 FIRKO &: }IA\'~: LARVAL WEIGl IT AND RESI!lTANCE IN TOJ\A(;CO J\UI)WOII~I

70

060LEA 50APIC ~O

E

30

T

4208H

10

0 20 40 60 80 100 120 1~O 160 180

WEIGHT. MG

Fig. 3. Plot of tol~rance v~rsus w~ight for H. virescens larvae treated with 0.1 "g cypermethrin per larva forurvae w~ighing 9.O-liS.4 mg. n = 241. For larvae <100 mg (n = 205) the relationship between tol~rance and.eight was linear. Least-squares regression equation. tolerance - 18.03 + O.25(weight), rt = 55%; P < 0.0001.

our tests was treated with as precise a dose as pos-sible with microapplication techniques. Resistanceto insecticides has a complex biological and geneticbasis (Georghiou & Taylor 1986). Absorption rates,transport through cell membranes, and various

Discussion

With topical application of insecticides, dosesthat individuals in particular treatment groups re-ceive and the actual amount of insecticide requir-ing detoxification vary slightly. Each individual in

30T 28

0

L 26ER 24AN 22CE 20

18

12

;.:1~::;.~5:~~:.

~.~.~:.~'~;.~~~WEIGHT. MG

rij:, ,t, PI'.I nf 1,.I,'r;III('(O "lor~II' "..it.:"1 for 11 rirl"$l"l"ns larvac Ircall"tl ,,'il" 1,0 /I~ cypt'rmclhrill IIt'r 1;lr".1 rIar\'O1I' \,('j~"",~ ",1-:11,1 "'~o" = 17;ll,('.I'I.~I'I"r\"" r('~rl""C"1 «:11"0111011, 1I,II"rO1I1"(' = 15,16 + UI7\\'I"I!:hll,

~_".."-

..

't

1225FIRKO 61 H'\I~ust 1990J()l'"~.\L OF ECONOMIC E~TO~IOU)(;Y '"m. ~'3" I\().

I .1. of deto,ification ;.

.'t~ f,I' .h;1nisms thOlt a fect all I

I"'~vite these fOl<.,tors, rt.'laticI" ~ :alld larvOlI \\'ei~ht \\'t.'rtc.IlK _I' _I S I1\.1l1lific:u 1n our sluuy, ma

:~~lIibc:al1l1Y afft.'cled e~prcs', Previous reports of suscep

-rtain size classes of H,1I1"~ b"based on one 0 servation pelt~rs 1982. Roush & Wolfenipeated observations of the scated that they responded dC)'perroelhrin. Some larvae lter 24 h later recovered corlI1ortality based on a single cduce bias against larvae in pabecause larvae in different \

difterently over time, By dt. molt (see Mullins & Pietersobserving each larva. we dmortality or tolerance diffeclasses beyond reported lirt\veen tolerance and weight.

Tolerance variation amorplaiDed by weight variation nany number of genetically 1anisrns. Because insect gro\\-tparticular stages are genetic{Zirkle & Riddle 1983; Via 1seau 1987), genetically baSt'affects tolerance variation. Ivariation in field populationsasynchronous hatch. food av.Although weight variation.fecting e~pression of toleraThrelationships bet\\'een toler.mediate expression of toleralused to improve the accurac.to predict the direction and e)in populations follo\ving in'For example. linear relatio!ance and ,,'eight can be incgene (Taylor 1983). multi-gtor quantitative genetic (Viaunpublished data) models.

Expression of tolerance Jweight to an even greatercations than in laborator)' stplications of insecticides, th.ceives depends partly on alength (its surface area). \\'cubed function of length (5,Small lan-'ae receive a largergram of body \veight, Becau~ical that an iI\dividllal call J,on the extent of its ml'tabollatiol\Ship bl't\Vt"l'lI tull'rol II.., ,be lilll'.'r III fii'ld "pplic.'atillholVl' all i'Vi'1I ~ri'atl'r "J\'a

sm.illl.lrvai' tlla'I lh.,t prC:illiTl'c:llllilllli'" th,lt ,II'III~ il"'l'"1)()(I~ ~i"l' li',t::, "pr.I~' labll' ,L

28T0 26LE 24RAN22CE 20

T 1872 16H

14

WEIGHT. MG

FiS. S. Plot of tolrrance vrrsus wright for H. vire$«n6 larvar treated with 1.0"g cypermethnn per larva forlarvae wrighing 25 :t 5 mg. n - 91. Least-squares rrgression equation. tolerance - 12.06 + 0.28(wright).

45

T 400LE 35RA 30NCE 25

T 202~H 15

so

WEIGHT. M6Fi~. 6. Pint of tolerance versus wei~hl for II. vircsccns larvar ~howinl; illtl'ractioll Ik'lwefOlI cl,- allcl ".,'i~ht.

Slop4.'s differ by a fact"" of thrl"t! arKl arc significanll~ diffcro-nt (/\~O\' ;\, l' < 005, so'e Tahh' 3). (:irl'h's al"IIII'I,,'rreJtre»iun lille, larv tr"';lIt-cl ".ith 0.1 ~~ cYllermethrili l)t'r larv;l; I;lrval ".,,'j~hts 9 ()-;J{;.3 IIIJt, " = I)lJ, tnl,'roll"'" =18.22 + O.25(wei~ht), " = OJ~, l' < 002. 1'1I.5(OS and lo"."r r"'~r"-Sc\H," lill", larva.. trc';ltl'tl with 1.0,,~ cYI1t'm",thrilipc:r larva; larval Wl'l~ht~ 9-1-:3Ii I mg. " = 1 i3. tul"ranc" - 13.M + U t).'S(wc-i~ht), ,: - 0.00, I' -: OIl;}.

I-"IRKO &. H,-\YES: LAI\\'AL WI::IGIIT AND RESI~I.~~CE IN TOnA(;(;(1 1\\'U\\'OI\~1'\lgust 1990

Tuhl.. 3. R...ull~..r ""uly.i. "r ".rill""'. 1'.~li"j: r.or ill"l~rDClio" 1.~lw~~n d~ ,.r cYI...r"".lhri" un.1 ij:hl ..f ",.'ir n. I"r.n~

~\\'t"ight~ x wei~htError

Analyzed variable: cumulative tolerance $COr.. throll!:h 2-1 h(T2-1h). Lar,'ae treated with 0 1 jig per larv» ,,'.,ighe.l !JO~'J(;.'}mg, n - 69; larvae treated with 1.0 jig per larva weigh...1 94-36.1 mg, n - 173. Mean squares (MS) are based on Type III slimsof squares. " Significant at P - 0.05; ._, significant at P = 0.001.

f!

may provide relationships between tolerance andweight that more accurately reflect field patterns.

If large larvae are more tolerant than smalllar-vae because they have more resources to fight theinsecticide. the significant interaction between doseand weight may result for purely physical reasons.For example. at 1.0 IJ.g per larva, 20 g and 100 glarvae have 2 g and 10 g of body \"eight. respec-tively, for each 0.1 IJ.g of insecticide. a differenceof 8 g. At O.llJ.g per larva. 20 g and 100 g larvaehave 20 g and 100 g of body \\.eight. respectively.for each O.llJ.g of insecticide. a difference of 80 g.At lower doses. large larvae have relati\"t'ly moreresources to fight a given amount of insecticidethan they do at high doses.

In H. vtrescens, as in other pest species. resis-tance has developed more slo\rly in tht' field thanin laboratory selection experiments (Bro\\.n 61 Payne1988). Any epigenetic factor affecting expressionof tolerance can potentially facilitate or delay de-velopment of resistance in the field. ~Iost epige-netic factors probably delay resistance develop-ment in the field because of increasedenvironmental variability in field populations rel-ative to laboratory strains. Delayed resistance inthe field can result from effects mediated by \\"eightif enough larvae survive field application bt'Causeof their large size alone. Differences bet\veen lab-oratory and Geld in the length of time required forthe development of resistance may be reduced byusing empirically derived relationships to correctfor the relatively high variability in weight andother epigenetic factors i~ field populations.

II\llds uf Jctc)xi(icatioll art' clllly ~Cllllt' of the'!II' 'h;aIli,~IfIS that .I(fl'ct .1.1 illCli\iclll..I's toll'r.\II<"e,"It" I f I ' I '

I..pilt' Ill'~' .Ic:tors, rt' .ltltIJI!' III'!' Ic't\\l'C'II lolt~r-

I"~, ,lIlt! l;arv.11 \vl'i~hl \Vl'rl' rt',lJily ooservt.'(1 and.1""IIli6eJ ill OIlr ~tlIJy, Small Ji[fl'rc'IICt.'s ill \veight"'~"i6C:'ll1tly affl'<:tt'tll'xprl'ssiml of toll'ranct.','I\;rrt'..iuus repurts of s'I~'t.'ptioility illl:rl'ases \vith-'1 ..'t'rt;aill siZl' l'lasses of 11. ciresccrls larvae \vere~ on one observatioll per larva (~Iullins & Pie-~rs 1952, Roush & Wolfenbarger 1985). Our re-~..ted observations of the same individuals indi.,",led that they responded differently over time toC)permethrin, Some larvae that appeared dead af.trr 24 h later recovered completely. Estimates ofmortality based on a single observation may intro-duce bias against larvae in particular \veight classes~ause larvae in different weight classes responddiHerently over time, By deleting larvae nearing, molt (see Mullins & Pieters 1982) and repeatedlyobserving each larva, we detected no consistentDlortality or tolerance differences among weightclasses beyond reported linear relationships be-l"een tolerance and weight.

Tolerance variation among individuals not ex-pi..ined by \veight variation may have resulted from,n\ number of genetically based tolerance mech-Jnisms. Because insect growth rates and ,veights atp;lrticular stages are genetically determined traits,Zirkle & Riddle 1983; Via 198-1a,b; Roff & Mous-5I:3U 198i), genetically based variation in weight,,(fects tolerance variation. However, most weight\OIri3tion in field populations probably results from..synchronous hatch, food availability, or nutrition.Although weight variation is only one factor af.fecting expression of tolerance, laboratory.derivedrelationships between tolerance and factors thatmediate expression of tolerance in the field can beused to improve the accuracy of models designedto predict the dirt.'Ction and extent of genetic changein populations following insecticide applications.For example, linear relationships between toler-ance and weight can be incorporated into single-gene (Taylor 1983), multi-gene (Plapp et al. 1979),or quantitative genetic (Via 1986; M,j,F. & j,L.H"unpublished data) models.

Expression of tolerance may be mediated byweight to an even greater degree in field appli-cations than in laboratory studies. With aerial ap-plications of insecticides, the dose that a larva re-ceives depends partly on a squared function oflength (its surface area), whereas its weight is acubed function of length (Schmidt-Nielsen 1972),Small larvae receive a larger dose of insecticide pergram of body weight. Because the amount of chem-ical that an individual can detoxify depends partlyon the extent of its metabolic capabilities, the re-lationship between tolerance and weight may notbe linear in field applications, Large larvae mayhave an even greater advallta~~ <:ompared \\'ithsmalll..rv..e ttlall tllilt prcuictl'tIIIY a lillear nI()(lel.TI:C"llilllll'~ tll,Il apply ill~l'l.ticiul' in IlroportiOJI toblKly ~iZl' (t',J;., spray l.II,lt' ill'I,lil"lliclIl tl'c:llllicl"t'S)

.~ .." .: -Aeknowledgment -

We thank Randy Bell for the loan of his microappli-

cation equipment and P. O'Brien for helpful discussions

on He/lothls toxicity tests. We thank G. Snodgrass, W.

Kitten, D, Wolfenbarger. R. Luttrell, J. Schneider, andJ. Mallet for their helpful comments on the manUScript.

r,-

37

'ght.,)pt"..'l' .hril.

Referenees Cited

Rrnwn. T. ~I. & G. T. ""YII", 1')1111. 1':'I"'filll'.'II,,1sc.,I,'clioll [()f inM.clici,le f",.,loIll"" J 1':"0111. Elllo"'111Is I: 19-5u. -

';',.".,.

~.E.~'"';, .;..

--- ...".--- , ':

.12%8 J()l:II~Al. ()I-' E(:O~()~ll(: 1'=~T()\l()L()(;\' \f.t. ""1. 'N,

Survey 4

North (

(Coleopto

D.C. HE

ABSTRACf LaboratorLeptinotarsa decemlinecicals registered for useextensive in potato beetlelevels of resistance alsoresistance was Inc.t prorrand carbof uran resistanCI:Results also showed sigm:counties. among 6elds w

KEY WORDS Insecta.

COLORADO POTATO BEETLE, Le

",.t"dta (Say), adults and larvae;;defoliators of commercially grsoIdnum tuberosum L., in the ~aTheir control has involved nearlJl"ncy on insecticides and has re~~'ere insecticide resistance prob\forgash 1981, 1985; Gauthier to

rl"Sistance is extensive, the costsistant beetles on potato is highl"~istence of the commercial pot.1985). Although many areas ofhave had severe problems \vitlt3nce of the Colorado potato beetit was not until the mid-1980~growers in eastern North Carcperience declining control of Cutie populations \vith pyrethroidinsecticides used frequently on

Managing resistancE' iequires .levels and distribut.on of resthroughout the pot~to-gro\ving ro( the spatial patterns of variatiois essential to an understanding'resistance (Tabashnik et al. 198~

- results o( a 2-yr survey done to l

terns of variation that exist invalerate, carbo(uran, and azin1=populations of Colorado potato bgrO\ving regions o( eastcrn Nort

n".."h. n. T. .\ J. ,\. M,.Kr,,~i,'. Ic'It.. 1-:c:,.I..~t'lIt1il'S "I illSt't:tiCitlc' :lilt! :It.,lril'it!t, r"".-I:lltt." ,'1:'"I\t... 1':lIt"",,,1 :);!: 3/;:!-:lkl) . I"

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Materials and Me

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