Resolving ambiguous results of host-specificity tesls

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spot (Cercospora solani melongenae Chupp.). A variety ofbroad-based pesticides was used against these pests, most of which are registered for other.
Resolving ambiguous results ofhost-specificity tesls:thecase0ftwo Leptinotarsa (Coleoptera: species Chrysomelidae) lorbiological control ol Sulanun elaeagnifoliumCavanilles (Solanaceae) inSouth Africa T.Olckersr & pE. Hullev'?

l2Plnnt Prute(tiottRescnrch his;tutc, prihfe BagXg05g,pictermaritzburs,3200SouthAlrico 'D.parlDttttI DfZnnloflttt'tdE Lot otogt,Rho(fus Lj irJersitV, Crahamstoton, 6140SouthAfrica Two lealfeeding chrysomelidsfrom North America,LeptinoLarsa texarm(Schaeffer)and Lltnot.:t:n dcftrh {Stiil), are promising candidatesfor the biological conrrol of soldrrlr, elnLngtiloliunCavanilLes(Solanaceae) in South Aftica. permissionior releasewas delayed becausethe.beetlesfed on cultivated eggplant (So/anrlrr,'lclofigcra Linnaeus)under cage conditions.After considerabledeliberationand further investig;tion,it was concluded that the resultsof the cagetestshad beenoveremphasized.The be;des were clearedfor release in SouthAfrica on the following grounds:(i) neitherL.,pfirotnrffspeciesattackseggplanr rn their native North American habitats; (ii) in South Aftica, many insect heriivores of Solanaceae feedon eggplantin cultivation but causeminor damagerelativeto cosmopolitan Polyphagouspests;(iii) as with L. tsirr?rd and L. defzcta, Conctrylocin rntrgfiu Olivie, a South African chrysomelidthat also occurson eggplantin cultivation, fed on eggplantin indoor cages,but preferredits natural Sold,'rrrhostsin largeoutdoorcages;(iv) eggiiantcultivation methods include crop rotation and severe pesticide regim;s, whic-h"should exclude Lepfirofals along with the other insects.This evidenceshowed that L. teMna andL. det'ccLa are,at the most, only a minor threatto eggplantcultivation in SouthAfrica, and the beetles were clearedfor releasein South Africa during 1992. Key words: Coleoptera,Chrysomelidae,LLTti\ttnlsa,host_specificity,Solanu,nelacag tloIi ta.Slfltu tnclottrrrn, weedbio(ontrol.

INTFODUCTION SolanumelaeagniloliunCavanilles (Solanaceae), eggplant if releasedin South Africa (Olckers & an exoticweed ofarableand pastoralland in South Zimmermann 1991;Olckers et a/.,in press). Africa, cannot be exclusively controlled by Eggplantis a minor veget,rblecrop in South conventional methods (Wassermannel dl. lggg). Africa and is grown throughout the country by The possibility of biological control is currently market gardeners(Annecke & Moran 1982;Bosch& centred around two leaf-feedingChrysomelidae, Oosthuizen 1987).The largest cultivations are in Leptitlotarsalexala (Schaeffer) and Lcptinotarsa the TransvaalLowveld,where eggplantis grown dcfa.,a (Stit), imported from North America.Ho*throughoutthe yedr as an annualcrop (Bosch& evet releasesof these two specieswere initially Oosthuizen 1987).To resolve whethir L. texann delayed becausethey deveioped on cultivated a\d L. tlefectashould be released or not, we eggplant (Solanummelongena Linnaeus)rn cages, investigated (i) cultivation practices in the even though the two specieshad never been Lowveld, (ii) attackby native Solarrm rnsectsand recorded from eggplant in their native North (iii) the effectol pesticides, currently usedon eggAmerican habitat (Neser et al. lgg} Olckers & ptant, on L. lcxanoand L. defucta. Zimmermann1991). Biologicalcontrol ot S,elaeagnifolium had co se- MATEFIALS AND METHODS quently reached a stalemate in that eggplant appeared to be a 'neutral' host and was thus Cultivationol eggptant unlikely to be immune to any folivorous agents The conditions under which etgplant is during specificitytesfs.ln spiteof this,it wasdrgued cultivated were determined by means of a that l?plinotnrsnspeciesare unlikely to attack questionnairesutvey during 1990,incorporating AfticanEntomology2(2)t jS7-144 (j954)

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the 11 most productive farms in an area around Kaapmuiden (25.32531.20E)and Louw's Creek (25.35S31.17E)in the TransvaalLowveld. Native insects on eggplant in South Alrica Surveysof the insectherbivoresthat attack eggplant were conductedon eachof the 11farms and included cultivations that had been treated with insecticidesas well as thosethat had not. Further collections were made in the eastern CaDe Provinceon eggplantin cultivdtionnedrBathuist (33.30526.498) and onexperimentaloutdoorplots at Grahamstown (33.19526.32E)and Uitenhage (33.43S 25.26E).On eachsamplingoccasion,collections were madeon at least20plants.Ectophagous herbivoreswere collectedin the field and parts of plants were taken for further examination.Stems were dissected to e\pose endophagous species and the foliagewas searchedfor'cryptic' folivores. Fruit and flowers were kept in emergencecagesto allow immature herbivores to complete their development.Voucherspecimensof unidentified insect specie5,referred to by their accession numbers, were placed in the Albany Museum, Crahamstown, and in the National Collection of Insects,Pretoria. Host-specificity tests with native beetles Of the native solanaceousbeetles,Colrcryloclexir frgrinnOlivier (Chrysomelidae)and Epilachnahirta (Thunberg) (Coccinelidae)are the most closely rclatedto Leptinotarsa speciesand alsoattackonly plants in the genus Solanun (Olckers & Hulley 1989a,b,1991).StaNation testswere carriedout on C. f(rina. Tenneonatelarvae were placedon each of the test species,which included potted eggplants and two native hosts,Solnnumlirtnneanum Hepper & Jaegerand SolanumcoccineutrJacquin. rearedtoadulthood and the Surviving larvaei^r'ere mortality and duration ofthe immature stageswas recorded. Ten replicates on each of the three specieswere carried out. Oviposition choice tests were carried out with C. tigrina and E. hirtn on potted plants in an outdoor walk-in cage.Eight pots of S.lirnacanult and eight pots of e8gplantwereplacedat opposite endsof the cageand40beetlesofeachspecieswere simultaneously released in the centre. Daily counts of beetles and eggs were made on the plants. At the end of each week, the beetleswere collectedand the plants changed.The freshplants were rotated to the oppositeends of the cageand

the beetleswere again released.The experiment was continuedfor four weeks. Pesticide trials PottedS.eLteIgnifoli& ll1plants were sprayedwith registereddosagesof the seven pesticidesmost commonly used on eggplantin the Lowveld. Two highly toxic chemicals, monocrotophos and profenofos,which are known tobelethal toa wide range of insectsand mites (Vermeulenef al. 1992), were not tested.For each of the sevenchemicals that were tested,therewere l0 experimentalplants and 10 unsprayedcontrol plants. Adults and late instar larvae of L. teani were tested separately. Five individuals were placedon eachplant, which wasenclosedby a 4l plasticcylindet theopen end of which fitted into the rim of the Dot. The cylinders were ventil.ited by 3 cm holei covered with gauze. The trials lasted 24 hours, during which feeding was monitored. Mortality was recordedafter 24 hours and monitored for uD to four weeksto confirm kills and allow pupaiing larvae to emerge.

RESULTS Cultivation ot eggplant On the 11 farms surveyed, eggplant occupied approximately6 % of the land under cultivation, confirming its status as a minor crop. Most growers (55 7.) planted one crop annually,while others planted two (18 %), three (18 %) and even tour (9 "/o)crops annually. Beforeplanting, Iands are deep-ploughed,fertilized and fumigated to conkol nematodes (Bosch & Oosthuizen 1987). Plantings occurred during most months of the year and plants remained in the soil for 9-12 months. Eggplant was rotated with a vadety of non-solanaceouscrops such as pawpaws/ beans, cucurbits,maizeand sweetcom,to limit the buildup of solanaceouspestsand diseases Red spider mite, Tefranychus cinnabarinus(Boisduval), was regardedby the growers as the most important pest, followed by lepidopterouslarvae (ASrolisspeciesand Helicoacrpaarmigera(Hibrter\) and aphids (Apl isld bneScopoll and Myzus persicae (Sulzer)).Theseare all polyphagousspecieswhich occur worldwide (Annecke& Moran 1982).Other pests included root-knot eelworms (Meloidogyne species:Nematoda)and diseasessuch asbacterial (Smith) Smith), wilt (PseLdomonas solanacearum

Olckers& HulleytHostspecificityin Leptinotarsa

139

Table 1. Pesticidesused on cultivationsot eggplantin the TransvaalLowveld. Chemical Miticides Chinomethionate Abamectin Insecticides Demeton-S-Methyl Monocrotophos(C) Dichlorvos Deltamethrin(C) Bifenthrin Dimethoate Profenofos C)4luthrin(C) (C) Endosulfan Fungicides Copperoxychloride l\,4ancozeb Metalaxyl Nemacides Aldicarb(C) Fenamiphos

Registrationon solanaceouscrops'z Red spidermite(G, To) Fled spider mite, rust mite (To) Red spidermite(To) Aphids(E, Pe, Po,To) Bed spider mite, rust mite (To);aphids (Po, Tb); Lepidoptera(Po, To); dipteranleaf miners(Tb,To);tobaccobeetle(Tb) Lepidopiera(To) Lepidopiera(To) Red spider mile, Lepidoptera,dipteranleaf miners (To) Aphids(Po,Tb) Red spider mite, thrips,dipteranleaf miners (To);aphids, Lepidoptera(Po, To) Lepidoptera(To) Aphids(Po);thrips(Tb);Lepidoptera (Tb,To) Blight(Po,To);bacterialspot(Pe,To) Blight (Po, To)i Fusaluar rot, scab (Po) Blight(Po,To) Aphids (Po, Tb); nematodes(Tb, To)jtobacco beetle,tobacco red mite (Tb) Aphids (Po); nematodes(Po, Tb, To);tobaccored mite (Tb)

I (C) ndicaleschemcals reg slered lorcoleopteian pesls inc !di.g ion solanaceolscfops) 2 E = eggp anl G = goosebetres Pe = peppers.Po = polatoes Tb = tobacco and To = lomaloes aner Vermeuen et at ( 1992).

fungal wilt (Ftst,"irn oxysporumlycopelsr.i(Sacc.) Snyder & Hansen),f:ungalblight (Alter aria solllli (Ellis & Martin) Jones& Grout) and fungal leaf spot (Cercospora solanimelongenae Chupp.). A variety ofbroad-basedpesticideswas usedagainst thesepests,most of which are registeredfor other solanaceouscrops (Table l). Pesticideswere applied at rates varying from once a week to once every three weeks, but most were applied once every two weeks. Highly toxic chemicals such as monocrotophos and profenofos were applied as required. Native insects on eggplant in South Africa Foufteen insect and two mite species,most of which attackthe foliage(Thble2),arelistedaspests ofeggplant (Annecke& Moran 1982).The majodty (75 Vo)are polyphagous and also pests of other, non-solanaceous crops,supporting the contention that generalistspeciesare the major pestsof eggplant. Our collections in the Transvaal and eastern Cape revealed 28 insect species that attacked eggpJant.of which at lea.t 17 species\^ere recruited from r.ative Solnnumspecies (Table 3).

Damageobsened on both vegetativeand reproductive tissueswas thus due to a combination of generalistand oligophagousinsects.Only 10 insect specieswere recorded on cultivations treated with broad-based pesticides and, with someexceptions,theseoccurredin fewer samples than on unsprayed cultivations (Table 3). The observabledamage on sprayed cultivations was limited becausethe numbers of individuals of eachinsectspeciesrecorded,although not quantified in thesesurveys,was always low. By contrast, unsprayed cultivations supported greater numbers of individuals and thus higher levels of damage. Host-specificity tests with native beetles Although larvae of the tortoise beetleC. fg,'ita took longer to develop on eggplant,mortality on eggplant was not significantly different from that on the two native So,irrr4 species(Table4). However,among the native hosts,larvalmortality was significantly lower and development quicker on S.linnaeanumthan on 5. coccineum. Theseresults indicate that eggplantis as suitableas the natural hosts of C. tigrina.By con&ast,eggplant was less

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Table2. Insectandmitespeciesrecorded as pestsot eggplantin SouthAfrica(afterAnnecke & Moran1982). Species COLEOPTERA Chrysomelidae Conchyloctenia hybi da 8dheman DIPTERA Anthomyildae Delia platura (Meigen') HEMIPTERA Aphidldae Aph,:slabaeScopoli MyzuspeBicae (Sulzet) Coleidae AnoplocnemEcuMipes(Fabticittsl Pentatomidae Nezae vitidula (Linnaeus, LEPIDOPTERA Gelechiidae Phthodmaea opercuIIeIa lzelletl Scrobipalpaheliopa(Lowet) Nocluidae Agrotis ipsilon (Hulnagel) Agtotis IongidentiIera (Hampsonl Agtotissegetum(Denis& Schiffermr.iller) AgtotissubalbaWalker HeIicoverya am igera (Hibnei THYSANOPTERA Thripidae ThtipstabaciLindeman ACARINA Eriophyidae Aculopslycope$ici(Massee, Tetranychidae Tetranychus (Boisduval) cinnabarinus

Pansdamaged

Host ranger

Foliage

Solanaceae

Stems& roots

Polyphagous

Foliage Foliage

Polyphagous Polyphagous

Growlhtips

Polyphagous

Foliage& fruit

Polyphagous

Foliage& stems Flowerbuds

Solanaceae Solanaceae

Roots& foliage Roots& foliage Boots& foliage Roots& foliage Foliage& huit

Polyphagous Polyphagous Polyphagous Polyphagous Polyphagous

Foliage

Polyphagous

Foliage

Solanaceae

Foliage

Polyphagous

1. Polyphagds species also anack plants tom fam li€s olher than Solanaceae

suitable than S. elaeagnifolium for L. fexanaand L. defecta(Olckers et al., in press). Conchyloctenia tigrina neverthelessdisplayed a strong feeding and oviposition preference for S,linnaeanumcompared with that for eggplant (Thble5), which was reminiscent of the preferences displayedby L. leranaar\d.L, det'ecta far S.elaeqgrifolium (Olcketset al., in press). The ladybird E. hifa, by contrast, showed no ovipositional preferences for its natural host, although it was encountered more frequently on eggplant(Table5). Epilachna hirta hasa wider host range than C. tigrina a d, unlike C. tigrira, also attackspotatoes(Annecke& Moran 1982).

Theseresults suggest that L, texafloarLdL. det'ecta, which have even nanower reported host ranges tha C. tigrina (Iacques7972;Hsiao 1974Table 3), are likely to be less of a threat to eggplant than C, tigrina. Pestlcide trials Miticides proved toxic to L. felar4, in particular the late instar larvae (Table 6). Although chinomethionate did not kill adults, it caused appreciable larval mortality, while propargite killed some adults and most of the larvae. Although feeding damagewas not quantified, it was apparent that both miticides inhibited adult

Olckers& Hulley:Host-specificity in Lepairotarca

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Table3. Inseclherbivores (UNS)cultivations associated withsprayed(SPB)and unsprayed oI eggplant (Solanummelongena) in SouthAlrica.Specieswherespecimens werefoundonly onceare excluded. Incidence is reflected as lhe percentage of thetotalnumberof samplesin whichtheinsectsoccufied.

Species FOLIAGE COLEOPTEBA Chrysomelidae Chaetocnemasp. (AcRh 465) Conchyloctenia hybida Bohema Conchyloctenia tigi na Oliviel Coccinelidae Epilachna hhla (f hunbeel Epilachna payku i Mulsanl Curculionidae Sciobius pulus (Sparrman) DIPTERA Agfomfzidae Liiomyzasp. Cecidomyiidae (AcRh 609) HEI\'IPTERA Cicadellidae AcRh 648 Coreidae C/etussp. (AcRh 526) AcanthocotisfasciolatusFabricius Anoplocnem is cuNi pes F abricius Lygaeidae Sp,Tostethus sp. (AcRh 574) Unidentifiedsp. Pentatomidae Nezara viridula (Linnaeusl HaIyd icoI us p re toi ae Dislan'l Unidentifiedsp. Membracidae Oryrach is delaknde i Faimaie Tingidae Urcntius hystice us lqichletl LEPIDOPTERA Noctuidae Eublemmasp. (AcRh 644) Helicoveea am igeta (Hibnet) Pardasena sp. nr diversipennis Gaede Gelechiidae Phthoi maea opercu Iella lzellet) FBUIT DIPTERA Lonchaeidae SiIba op hy toides (Bezzi) Muscidae Atherigona sp. (AcRh 470) LEPIDOPTERA Pyraustidae Daaba hisalis (Walkei

lncadence SPR UNS

Host ranger

1

100 33 56

50

89 33

Oligophagous(8) Oligophagous(7)

22

Unknown

22 44

Polyphagous (1) Oligophagous

33

Oligophagous(4)

50

44

50

44

Unknown Oligophagous(8) Polyphagous

50

-

33

(11) Oligophagous Oligophagous(7) Oligophagous(7)

l1

Polyphagous Unknown

1',| 1l

Polyphagous Unknown Unknown Oligophagous(8)

11

Oligophagous(4)

33 11 22

Oligophagous(8) Polyphagous Oligophagous(2)

1l

Solanaceae

50

(3) Oligophagous

75

(3) Oligophagous

100

(8) Oligophagous

AfricanEntomology Vol.2, No.2, 1994

142 Table3 - continued

FLOWERS COLEOPTERA Nitidulidae Pr,,ia sp. (AcRh504) LEPIDOPTERA Gelechiidae Scrobipalpasp. nt. corcrefa (Meyrick)

33

83

(7) Oligophagous

100

(8) Oligophagous

1. Oligophagols nsectsattack on y So/arum planG nlrnbers n brackeb srgnilyrhe numbefol nat ve So/anum hosls Po yphagous nsectsalso atack panls lrom lami es otherlhan Solanaceae

Table 4. l,rean (1 S.E.) mortality and developmental Tabfe 5. Host selection by adults ol Conchyloctenia duralion ol Conchyloctenia tig na laNae rcared on eggtigina and Epilachna hirta as determined by their mean planl (Solanum melongenal and two native So/anum (1 S.E.) distribution and oviposition on eggplant sDecies. (Solanum melongena) relative to the native So/anum linnaeanumin a ouldoot cage. Plant species S. linnaeanum S. melongena S. coccineum

Mortalityr 1.4I 0.3 a 2 . 5 1 0 . 5a b 3 . 6 1 0 . 9b

Duration(days)' 30.3t 0.2 a 3 4 . 0 1 0 . 4b 32.2!0.5c

1 Meanscomparedby o.e-way ANOVA|lhose lollwed by lhe same letlef are nol sig.ilicanlly difierenl(P > 0 05iDuncans mulliplerangetest)

and larvalfeeding.By contrast,control plantswere totally defoliated. In cultivations, miticides are applied weekly to once every two weeks, suggesting that they may themselves exclude L. texarut. The systemic insecticide demeton-S-methyl, registered for aphids, was ineffective against L. texanoadlilts but killed most larvae. Contact insecticides,used againsta variety of pests,were the most toxic of the pesticidesto L. texana(Table 6). Endosulfan was the least toxic and slowest acting, while dichlorvos, deltamethrin and cyfluthdn were 98-1007olethal,and had an immediate effect. Inhibition of feeding was also observedwhere the insecticideswere lesseffectiveor did not act immediately. Many of the contact insecticidesare registered for coleopteranpests (Table 1) and regular applications of these will preventL. /.xdrafrom survivingon eggplant.

Distributionr

Ovipositionr

C. tigrina S. Iinnaeanum S. melongena

1 2 . 3i 0 . 8a 1 . 5 1 0 . 3b

2 1 . 5 : r3 . 9a 4 . 6 1 1 . 6b

E. hina S. linnaeanum S. melongena

7.1 ! 0.5 a 1 1 . 9r 0 . 5 b

8 0 . 2 1 1 5 . 8a 1 0 8 . 2 11 6 . 4a

Plantspecies Insect species

L Mea.s compa€d by one way ANQVA those follMed by lhe same bner are not sign icanty difterenl( P > 0.05i Duncans mulliplerangetesl)

recruited from native Solanum species, as these may indicatethe possiblefate of imported biocontrol agents. None of the native oligophagesare re8ardedas pestsof eggplant,for one or more of the following reasons: 1. Indigenous insect species associated with Solanun gerreftlly have a narrow range of alternative hosts and originate from small populations that occur on sparsely distdbuted plants. Their incidenceon eggplant is overshadowedby other generalistpests,which arequick to reacheconomically damaging thresholds. 2. Of the several native herbivore speciesthat can survive on eggplant, most apparently prefer their natural Solanumhosts, as did the native DtscusstoN chrysomelidC. tigrinl. Larrae ol C. tigrina developed more slowly on eggplant, which would inOur surveys revealeda far greater diversity of crease their exposure to natural enemies and insectsinjudous to eggplant than reported in the insecticides(Brown et al.'1980\. literature (Annecke& Moran 1982).Of particular 3. The small areasunder cultivation, as well as interest were the many oligophagousspecies rotational practices,makeseggplant lesspredicF

Olckers& Hulley:Host-specilicityin Leptinotarsa

14i)

Table6. Percentage modalityof adultsandlaNaeol Leptinotarsa texanafollowing exposure plants.lrortalitywasrecorded to pesticides appfiedto Solanumelaeagnitolrum after24 hours andagainafterfourweeks.

Chemicall

(lvl) Chinomethionate Control (l\il) Proparagite Conkol Demeton-S-methyl (Sl) Control (Cl) Endosulfan Control (Cl) Dichlorvos Control (Cl) Deltamethrin Control cyfluthrin(cl) Control

24 hours

4 weeks

0 0

0 0 40 4 I 2 64 2 98 I 98 0 98 0

2 0 2 't0 0 98 8 98 0 98 0

24 hours

4 weeks

38 0 0 0 18 0 54 0 100 0 '100 0

84 0 60 0 70 10 a2 6 100 0 100 0 100 2

0

L M = milicide,Sl= syslemrc nsecticide Cl= contact nsectcide

able and vulnerable to oligophagousinsectsfrom other Solarumspecies. 4. Intensive applications of broad-basedpesti cides againstgeneralistpestsalso suppressdamageby Solaramoligophages. Similarly, L, fexanaa\d L. deFcfaare unlikely to become pests of eggplant for the following reasons: l. Neither speciesaftackseggplantin theAmericas (Olckers& Zimmerrnann 1991;Olckers et al., in press).Certainly,their reportedhostranges(Jacques1972;Hsiao 1974)arefar narrower than those of many South African solanaceouschrysomelids (Olckers& Hulley 1989a,b,1991).In common with C. tiyina, both L. temno and L. det'ectadeveloped on eggplant,but showed strong oviposition preferencesfor their natural hosts (Olckers et a/., in press). 2. In contrastto the situation in North America, major eggplantcultivationsdo not overlap with S. eheqg tfoliuminfestationsin SouthAfri ca.Leptinotnrsatenna and L. defecta are thus unlikely to have accessto eggplantcultivations. 3. Should host expansion and colonization of eggplant neverthelessoccut eggplant cultivation practiceswould curb establishment.Crop rotation would disrupt beetle populations. Rotation of potato crops is used effectively as a control

stlategy to limit colonization by post-diapause (Say),in Colondo beetles,Leptinotarsa decemlineafo the U.S.A. (Hare 1990).Furthermore, L. decemlircatdin rotated potatofields have lower levelsof pesticide resistancethan in non-rotated fields, sincerotationindirectly reducesselectionfor resistanceby reducing the frequencyof sprays(Roush elrl. 1990).Regularsoil fumigation for nematodes should cause mortality in pupating larvae and diapausing adu lts of L. temna and L, det'ecta,whtle foliar applications of insecticidesand miticides will kill feeding adults and particularly laryae. Copper-basedfungicides,which are also used in South Africa (Thble 1), inhibit feeding by L. decen /ircafaand reducedamageto eggplantoltivations in the U.S.A.(Hare 1984,1990)and should do the samelo L. fexotlaa\d L. defecfo. In conclusion,there is no reasonto suspectthat L. texona and L. defectI will cause significant problems on eggplant. Many solanaceousherbivores cause extensive damage to eggplants in cagesand evenattackeggplantin the field,but are not regarded as pests either by farmers or from reportsin the literature.This supportsour conclusion that eggplant is a 'neutral' host but is not tlueatened by oligophagous leaf-feederswhich are not normally associatedwith it. Theseconsiderations support the contention of Olckers &

African EntomologyVol. 2, No. 2, 1994 Zimmermann (1991) and Olckers ef ni. (in press) that L. texana a\d L, defecfa do not threaten eggplant cultivations in South Africa and that their lelease in South Africa for the biocontrol of S. elaeagnifolium is fully justified. ACKNOWLEDGEMENTS We thank R.L. Kluge, M.P Hill and anonymous referees for comments on the manuscript. The following are acknowledged for providing infor-

mation on the cultivation of eggplant and for alIowing collections on their farms: P Caetano, R. Colmanet, W Colmanet, A. Elliot, B. Glanville, N. Grobler, W Kotze, W. Mathewson, A. McDonald, K. Mullins and D. Secco.We are grateful to the following pesticide companies for providing samples of their products for use in the pesticide trials: Bayer South Africa (Pty) Ltd, Ciba-Geigy (Pty) Ltd, Chemfit (Pty) Ltd, HoechstSouth Africa (Pty) Ltd, Shell south Aflica (Pty) Ltd and Uniroyal Chemical (Pty) Ltd.

REFEBENCES ANNECKE, D.P & MORAN,V.C.1982.b$ectsatd Mites of Cultionted Plants i1t South Afii.d. Butterworths, Durban. BOSCH, S.E.& OOSTHUZEN, A.S.A. 1987.Egg-ftuit prcduction. Tomatoes,peppersand egg-frlrit.Fal,rt 1-4. ing it1Sotfh At'ticaA.1,119a7: BROWN,I.J.,JERMYT.& BUTT,8.A.1980.The influence of an alternativehost plant on the fecundity of the Colorado potato beetle, Leptitlotarcadccenlineata (Coleoptera:Chrysomelidae).An,nls of lh. EnfomoIogicalSocietyof America73t 197-199. HARE, J.D. 1984.Suppressionof the Colorado potato beetle, Leptinotarca decemlitlcata(Say) (Coleoptem: witha copperChrysomelidae),onsolanaceouscrops Etltonology13:10L,-. basedfungicide. Enrrironmental 1014. HARE, J.D.1990.Ecologyand managementof the Coloof Enfolllology351 mdo potato beetle.Arnual RenieTo 81-100. HSIAO,T.H. 1974.Chemicalinfluenceon feedingbehavio\t of Leptinotnrcnbeetles, ln: Browre, L.B. (Ed.) Experinental Analysis of Insect Behaoiour.237-247. Springer-Verlag, New York. JACQUES,R.L. 1972.Taxonomicrevision of the genus Leptinotarsa(Coleoptera:Chrysomelidae)of North America.Ph.D.thesis,PurdueUniversity,Layfayette. NESER,S.,ZIMMERMANN, H.G., ERB,H.E. & HOFF. MANN, J.H. ]990. Progressand prospectsfor the biological control of two Solanumweeds in South Africa. In: Delfosse, E.S. (Ed.) Proceedings of the SeoenfhInfclnafiotlalSymposiutn on BiolosicalControl of W:eds.371-381.lstitnto Sperimentale per la Patologia Vegetale,Italy. OLCKERS.T. & HULLEY PE. 1989a.Insect herbivore diversity of the exotic weed Solant writianwn Scop.and threeother Sol4nrnrspeciesin the eastem Cape.louftal of the EntotlologicalSoci.tllof Sottthem Atuica52:8143.

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