PARASITES OF THE EUROPEAN CORN BORER (LEPIDOPTERA: PYRALIDAE) IN SOUTH CAROLINA'

PARASITES OF THE EUROPEAN CORN BORER (LEPIDOPTERA: PYRALIDAE) IN SOUTH CAROLINA' J. A. Wilson, Jr.' and J. A. DuRant Department of Entomology, Clemson University Pee Dee Research and Education Center Florence, South Carolina 9501-960 ABSTRACT A survey of the parasites of the egg, larval, and pupal stages of the European corn borer (ECB), Ostn'nia nubilalis (Hubner), was conducted in the Pee Dee and [\'lidlands regions of South Carolina during 1986-1987. The egg parasite survey also included 1985 and 1988. European com borer larvae and egg masses were collected primarily from com, Zea mays (L.). However, they also were collected from broadleaf dock, Rumex obtusifolius L., curly dock, R. crispus L., Irish potato, Solanum tuberosum L., sorghum. Sorghum bicolor (Lo), and wheat, Triticum aestivum L. Four parasite species were reared from ECB larvae: Lixophaga 51'. ncar uan"abili.<; (Coquillett), /...ydella thompsoni Herting, Pristomerus Sp;lIC1tor (F.), and Agathis agilis (Cresson). Three species of egg parasites were recovered: 7'richogmmma pretiosum Riley, 'I: exiguum Pinto and Platner, and 7'. (uentesi Torre. Lixophaga sp. near ooriabilis wus the most abundant parasite and was collected from six of the seven counties surveyed. In 1986 this tllchinid was reared from 6.0 and 9.0% of second lind third generation ECB fifth instar lorvae, respectively. The introduced parasite L. thompso1l; was reared from 4.% of the first generation ECB larvae couected from curly dock during 1986-1987. Key Words: European corn borer, Ostrillia "ubilalis (Hubner), J)ol'asitcs, biological control, Lepidoptera, Pyralidae. J. Agrie. Entomol. 8(): 109-116 (April 1991) The European corn borer (ECB), Ostrinia. nubilalis (Hubner), was first detected in the United States near Boston, Massachusetts in 1917 (Brindley and Dicke 196). During the 1960's it became established throughout South Carolina (DuRant 1969), where it is now a serious pest of several crops including corn, sorghum, and cotton. Up to four ECB generations per year occur in South Carolina. Diapausing mature larvae overwinter inside host plant material and moths emerge during April and May (DuRant 1969). The relatively low value of corn and sorghum, the difficulties encountered with insecticidal control of this pest on both corn and cotton (Umeozol' et al 1985, Savinelli et al. 1986), and increasing environmental concerns make biological control an attractive alternative. Brindley and Dicke (196) cited the lack of native parasites as a factor which has contributed to the success of the ECB in the United States. Attempts to establish exotic parasite species during the first half of this century resulted in 6 of 4 species becoming permanently established (Baker et a1. 1949, Brindley et a1. 1975). Recently, entomologists have expressed renewed interest in importing exotic ECB parasite species. Since the earlier attempts at biological control occurred prior to the Received fof" publication 6 July 1990; accepted 18 October 1990. Del)8rtment of Fertilizer lind Pesticide Control, P.O. Box 179, Columbia. SC 91. 109

110 J. Agric. Entomol. Vol. 8, No. (1991) establishment of the ECB in South Carolina, little is known about the parasite species in this state. This study was conducted to determine the parasite species composition and incidence of EeB parasitism occurring at selected locations in the Pee Dee and Midlands regions of South Carolina. MATERIALS AND METHODS One or two fields were surveyed in each of seven counties during 1986: Darlington (I), Dillon (), Marlboro (), Lee (4), Sumter (5), Lexington (6), and Newberry (7) (Fig. 1). These same locations were surveyed again in 1987, except the Lexington and Newberry locations were omitted. For all counties except Darlington and Dillon the only host plant species sampled was corn, Zea mays (L.). In Dillon County, wheat, Triticum aestiuum L., was sampled in 1987 in addition to corn. Plants sampled at the Darlington location were corn (1986, 1987); sorghum, Sorgh"m bicolor (L.) (1987); curly dock, Rumex crispus L. (1986, 1987); broadleaf dock, R. obtusi[olius L. (1987); and Irish potato, Solonum tuberosum L. (1987). Randomly selected plants were dissected and all ECB larvae and pupae and parasite puparia were collected. The number of ECB's per sample varied greatly depending on the ECB population density. AU collections were made during the growing season (May August) except for 10 diapausing ECB lalvae which were collected from com in Darlington County in November, 1986. These 10 larvae were placed in 0-ml diet cups containing ca. to ml of Bio-Mix artificial diet #9478 (Bio-Serve Inc., Frenchtown, New Jersey) and placed in a rearing room at 8 C and an 18:6 LD photoperiod to break diapause (McLeod Bnd Beck 196). Larvae collected during the growing season were placed on this diet and held at room temperature (4-8 C) under constant light. ECB pupae and parasite puparia were treated similarly, but the cups contained no diet. AU specimens were observed daily until moths or pamsites emerged. Dead ECB's were dissected and examined for parasites. Larval instars were determined by measuring head capsule widths using a binocular microscope equipped with an ocular micrometer. ECE egg masses were collected from COl'll in Dillon County in 1987, and from the following plants in Darlington County: corn (1985, 1987, 1988), Irish potato (1985, 1986), and Rumex spp. (1987, 1988). Egg masses were placed in 0-m! diet cups containing moistened pieces or paper towel, held in the laqol'atory as described above, and observed daily until eclosion or parasite emergence occw'i'ed. All parasite specimens were forwarded to specialists at the Biosystematics and Benelicial Insects Institute at Beltsville, Maryland for identification. Voucher specimens of ECB adults and parasite adults were placed in the Clemson University Insect Museum. RESULTS AND DISCUSSION 1986 Twenty-seven ECB pupae and 56 larvae were collected May - August. These included 19 third instal's, 140 foul"t.h instal's, und 67 fifth instal's. Thirty-one larvae (5.9%) were parasitized (Table 1). Twenty-five of these larvae (1 fourth instal' and 4 fifth instal's), all from corn, were parasitized by Lixophaga sp. near variabilis (Coquillett) (Diptera: Tachinidae). This species was collected from all counties except Lexington, where only seven ECB larvae were found. Andreadis (198)

WILSON and DU RANT: Europcan Com Borcr Parasitcs III 7-1 4 5_ 6- Fig. 1. European corn borer parasite survey locations in South Carolina, 1986 1987. Locations 6 and 7 were omitted in 1987. Table 1. Parasites reared from European South Carolina counties, 1986. com borer (EeB) larvae fl'ol11 seven County (ECB No. ECB No. % Parasite generntions, host) J8Ivae parasites parasitism species* Darlington 14 10 7.5 LV (I,, ; corn) Darlington 68 6 8.8 LT(5), AA(I) (I, curly dock) Dillon 87. LV (, ; corn) Lee 1.6 LV (, corn) Lexington 0 0 0.0 (, corn) Marlboro L4.J LV (1,, ; corn) Newberry 6 6 16.7 LV (, corn) Sumter (, ; corn) l7 5.9 LV Total~ 56 1 5.9 LV l"cllresents Lixophaga SJl. nem I,}{lriabilis (Coquille!). 1':1' represents Lydclla tllomp;ulfli Hert.ing, AA represents Ag(llhi,~ agi/is (Cresson).

11 J. Agric. Entomol. Vol. 8, NO. (1991) reported that the native parasite Lixophaga sp. was widespread in Connecticut but that it appeared to have no significant controlling effect on ECB populations, and Peail's and Lilly (1975) found low infestation levels of a species of Lixophaga in Massachusetts. We found parasitism of fifth instal' ECB larvae by Lixophaga sp. near uariabilis to be quite variable, ranging from 0.0 to.% (Table ). Much of this variability undoubtedly was due to the low numbers of larvae collected from fields containing extremely low ECB infestation levels. Although greater numbers of larvae would have been desirable, this was impractical because of the searching time required. Table. Parasitism of fifth instar European corn borer (ECB) larvae infesting corn in seven South Carolina counties by Lixophaga sp. near vanabilis (Coquillett), 1986. County Darlington ECB generation No. ECB larvae 78 18 % parasitism 5.1. Dillon 10 51 0.0.0 Lee Lexington 1.1 7 0.0 Marlboro 1 11 57 46 0.0.5. Newberry 8 1.4 Sumter 9 5 11.1 0.0 Totals 11 167 155 0.0 6.0 9.0 The remaining six parasitized larvae were first generation larvae from curly dock in Darlington County. Three fourth instal' lalvae and two fifth instal' larvae were parasitized by Lydella thompsorji Herting (Diptel'a: Tachinidae) and one third instal' lmva was parasitized by Agathis agilis (Cresson) (Hymenoptera: Bl'aconidae). Lydella thompsoni, first imported from Europe in 190, was once the most widely established and effective ECB parasite in the United States (Baker et al. 1949, Brindley and Dicke 196). This tachinid gradually disappeared in the 1960's (Hill et al. 1978, Andreadis 198). Burbutis et al. (1981) successfully reestablished L. thompsoni in Delaware in 1975-1976. Interestingly, this species was collected from

WILSON and DU RANT: European Com Borer Parasites 11 caged corn stalks infested with overwintering ECB larva from Charleston, Dillon, and Florence Counties during 1971-197 (J. A. D., unpublished data) when it apparently had died out elsewhere in this country (C. W. Sabrosky, U. S. Dept. of Agriculture Systematic Entomology Laboratory, Beltsville, Maryland, personal communication). No parasites were reared from the 7 ECB pupae or from the 10 diapausing larvae. Adult tachinids emerged from 1 of L7 puparin collected from ECB tunnels in corn during May - August. Six of these from Newberry, one from Marlboro, and three from Sumter County were Lixophaga sp. near uariabilis and two from Sumter County were L. thompsoni. /987 A total of 1110 ECB larvae including 0 second instal's, 4 third instars, 404 fourth instal's, and 4 fifth instars were collected. Only 4 of these (.%) were parasitized (Table ). Lixophaga sp. near uadabilis was reared from 1 third generation fourth instar larva from sorghum in Darlington County and from 1 second generation (1 third instar and 11 fifth instar) larvae from corn in Lee County. Table. Parasites reared from European corn borer (ECB) larvae from five South Carolina counties, 1987. County (ECB No. ECB No. % Parasite generations, host) larvae p8l'asites parasitism species Darlington 60 0 0.0 (I, brondlear dock) Darlington 117 4.4 LT(), AA(I) (I, curly dock) Darlington 1 4.6 PS (I, Irish potato) Darlington 74 1.4 LV (, sorghum) Darlington 17 5. PS (I,, ; corn) Dillon 77 0 0.0 (I, whent) Dillon 97 0 0.0 (I,, ; corn) Lee 17 1 9.5 LV (I, ; corn) Marlboro (I. ; corn) 90 1.1 PS Sumter 9 0 0.0 (I, ; corn) Totals IllO 4. 1..:1' rcllresctll<; L}lJdla tjlom/lsoni Her1in~. AA represent!' Agathis ngili.~ (Cresson), PS rcpre!;cnls P7i.~II)mcnl.~.~pill(j/fJr (F.), LV represent.s tix/jphngfl 5p. nenr vnnnbilis (Coquillel,!).

114 J. Agric. Enlomol. Vol. 8, No. (1991) Three additional parasite species were reared from first generation ECB larvae. Lydella thompson; was reared from 1 of 47 third instar larvae and from of 60 fourth instar lan'se infesting curly dock in Darlington County, and A. agilis was reared from 1 of these 47 third instar lalvae. Pnslomerus spinalor (F.) (Hymenoptera: Ichneumonidae) was reared from 1 of 11 second instar larvae, of 47 third iostar larvae, and of 9 fourth instar larvae infesting corn in Darlingt.on County; from 1 of 7 fourth instar larvae infesting Irish potato in Darlington County; and from 1 of 9 third instar larvae infesting corn in Marlboro County. In 1984 this parasite was reared from of 95 first generation ECB larvae collected from corn in Dillon County (J. A. D., unpublished data). Prior to this, P. spinator had not been recorded as a parasite of the ECB (R. W. Carlson, U.S. Dept. of Agricultw'e Systematic Entomology Laboratory, Beltsville, Maryland, personal communication). Additional parasite species reared from the ]984 Dillon County collection but not recovered during the current sul\!ey were Diadegma sp. (Hymenoptera: Ichneumonidae), Apanteles sp. (Hymenoptera: Braconidae), and Orgilus sp. (Hymenoptera: Braconidae). This was the first report of ECB parasitism by OrgiLus sp. (P. M. Marsh, U.S. Dept of Agriculture Systematic Entomology Laboratory, Beltsville, Maryland, personal communication). A single colony of the gregarious braconid Apanteles pyralidis Muesebeck was reared from an ECB larva from Indiana in 190 (Baker et al 1949). During 1989 two additional parasite species were reared from ECB overwintering in sorghum in Darlington County (J. A. D., unpublished data). One specimen of Spilochalcis side (Walker) (Hymenoptera: Chalcididae) emerged from a pupa and one specimen of Lespesia archippiuora (Riley) (Diptera: Tachinidae) emerged from a larva. Egg Parasites Three species of rrru.. /logramma (Hymenoptera: Tlichogrammatidae) were reared fl'om 464 ECB egg masses: T. pretiosum Riley, T. exiguum Pinto and Platner, and T. [uentesi Torre (Table 4). This genus is known for its great diversity of hosts (Ridgeway et al. 1981). TricJwgramma nubilale Ertle and Davis, which appears to be selective for the ECB (Curl and Burbutis 1978), was not collected. Four of 50 first generation egg masses (8.0%) collected from Irish potato in Darlington County in 1986 contained eggs parasitized by T pretiosum. In 1987 T exiguum parasitized eggs in 1 of 106 second generation egg masses (1.%) collected from com in Darlington County and in 6 of second generation egg masses (17.9%) collected from corn in Dillon County. Five of first generation egg masses (.7%) collected from Rumex spp. in Darlington County in 1988 were parasitized by T exiguum and T [uentesi. Although parasite species were not determined for all egg mass collections, all appeared to be Trichogramma spp. This study, including the 1984 and ]989 data, revealed that at least three dipterous and nine hymenopterous species arc parasites of the ECB in South Carolina. Lixophaga sp. near variabilis was collected most frequently, being recorded from six of seven counties in 1986 and two of five counties in 1987. This species was collected only from second and third generation ECB larvae. Lydella t./wmpsoni was reared from ECB larvae infesting curly dock in Darlington County during 1986 and 1987 and from overwintering ECB larvae in Dillon and Charleston Counties during 1971 197, indicating that this species is primarily a parasite of overwintering and first generation larvae. Pristomerus spinala,. was reared from

WILSON and DU RANT: European Corn Borer Parasites 115 Table 4. Parasitism of European corn borer (ECB) egg masses, 1985-1988. No. egg masses % parasitism County (ECB generations, Avg. no. Egg Individual Parasite (year) host) eggs/mass masses eggs species Darlington 56 (1, Irish 1.9 5.4 1. (1985) potato) Darlington 100 (. corn) 5.1 4.0 0. (1985) Darlington 50 (I, Irish 1.4 8.0.0t Trichogramma (1986) potato) pretiosum Darlington 4 (I, Rumex spp.) 15.8 8.8.0 (1987) Darlington 106 (, ; corn) 1.9 1. T. eriguum (1987) Dillon (. ; corn) 19.5 17.9 T. exiguum (1987) Darlington (I,!?W71CX spp.) 0.9.7 7.8 T. exiguum (1988) T.. /uelltesi Darlington 1 (, corn) 1. 9.5. (1988) Darlington '1 (, corn) 19.6 0.0 0.0 (1988) Undetermined. t AI>llroximale. first generation larvae from Dillon County in 1984 and rrom Darlington and Marlboro Counties in 1987, but was not collected in 1986. This study indicates that although several ECB parasite species occur in South Carolina their overall impact on ECB population levels is I'clatively insignificant. However, the permanent establishment of L. thompsoni is encouraging. Additional investigations are needed to determine the biological control potential or this and other parasites against ECB in South Carolina. ACKNOWLEDG:liIE. T The authors thank the specialists who identified the parasite species collected during this investigation. All cxcept V. I<. Gupta nre associated with t.he Systematic Entomology LaboTatOlY. G. S. Department of Agriculture: C. W. Sabrosky and N. E. Woodley rrachinidae), D. L. Vincent. (Trichognnnmatidae), P. ~!1. t\. Jarsh (Brnconidac), E. E. Grisscll (Chalcididae), R. \V. Carlson nnd V. I<. Gupla (Entomology lind :-JcllIfltology Dcpartlnen\., University of florida) (lchneumonidllc). This paper is technical contribution no. 069 of the South Curolinn Agricultural Experiment Station. Clemson University. REFERENCES CITED Andrcadis, T. G. 198. Current slatus of imported and nath'e parasites of t.he European corn horer (Lepidoptera: Pyralidae) in Connecticul. J. Beon. Entoma!. 75: 66-69. Baker, W..0\., W. G. Bradley, and C. A. Clark. 1949. Biological control of the European corn!lore!' in Ihe United States. U, S. Department of Agriculture Technical Bulletin 98, WashingtOn, D. C,. 185 PI'.

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