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Nosema pyrausta infection in Macrocentrus grandii, a braconid parasite of the European corn borer, Ostrinia nubilalis
JOURNAL
OF INVERTEBRATE
PATHOLOGY
35,229-233
(1980)
Noserna pyrausta Infection in Macrocentrus grandii, a Braconid Parasite of the European Corn Borer, Ostrinia nubilalis THEODOREG.ANDREADIS Department
of Entomology,
Connecticut
Agricultural
Experiment
Station,
New
Haven,
Connecricur
06504
Received May 29, 1979 Macrocentrus grandii which develop within Nosema pyrausta-infected larvae of the European corn borer, Ostrinin nubilalis, develop direct systemic infections from the ingestion of spores at the time of larval emergence from the host. Infections adversely affect pupal development and adult longevity. Infected females are unable to transmit the microsporidian to additional corn borer hosts. Pathogen development in the parasite host appears identical to its development in the corn borer host and mature spores show no morphological differences in size or shape when observed at the ultrastructural level. The prevalence of infection in natural parasite populations is 53.8% and closely parallels the 56.7% prevalence of infection in corn borer populations. Results suggest N. pyrausra may play a significant role in limiting M. grandii populations when levels ofN. pyrausta in corn borers are high. KEY WORDS: Nosema pyrausta; Macrocenrrus grandii; Ostrinia nubilalis; natural infections; development; survival; longevity.
INTRODUCTION
The susceptibility of insect parasites to microsporidian pathogens of their hosts is well known and has been reviewed (Brooks, 1973). In most instances, parasites which develop within infected hosts fail to mature, or if they do, develop into weak adults which are short lived and exhibit reduced fecundity. These detrimental effects generally result from the direct infection of the parasite by the pathogen but may also occur when large numbers of ingested spores accumulate in the parasite’s midgut. When direct invasion does occur, pathogen development within parasitic hosts has been shown to be similar to that which occurs in its normal host, but may result in changes in spore size (Brooks and Cranford, 1972). In 1926, a polyembryonic braconid parasite, Macrocentrus grandii, was introduced into North America for control of the European corn borer, Ostrinia nubilalis. It became the predominant parasite of the corn borer in Connecticut, but the prevalence of parasitism never exceeded 28% (Baker, 1958) and its inability to reduce corn borer populations significantly was never com-
pletely understood. During laboratory rearing of M. grandii, York (1961) observed mortality in the parasites prior to pupation. Although no details were provided, he attributed this to infection by Nosema pyrausta, a well-known and widespread microsporidian pathogen of the corn borer host. This study was undertaken to identify and investigate the development of this microsporidian pathogen in M. grandii, to quantify its effects upon the host, and to determine its prevalence in natural parasite populations. MATERIALS
AND METHODS
Healthy and N. pyrausta-infected M. grandii were obtained from mature European corn borer larvae collected at Lockwood Farm in Hamden, Connecticut, during October and November 1978. Corn borer larvae were isolated in 1-oz plastic containers supplied with corrugated cardboard squares and moist filter paper disks to maintain high humidity, held. at 25°C under constant light, and examined daily for larval emergence of M. grandii. Records were kept of the number of M. grandii larvae, pupae, and adults obtained 229 0022-201 l/80/030229-05501.00 Copyright All rights
0 1980 by Academic Press, Inc. of reproduction in any form reserved.
230
THEODORE
from each corn borer host. Sibling adult parasites (obtained from a single host) were collectively transferred to l-pint screened paper containers supplied with plain water and honey and maintained at 25”C, relative humidity 75-80% under an 18-hr photoperiod. Adult mortality was recorded daily. N. pyrausta infection in M. grandii was determined by direct examination of tissues for spores under phase-contrast microscopy following death of the parasite. Nonparasitized corn borer larvae were held until adult emergence or death and then examined for N. pyrausta and larval parasites which may have failed to develop. To confirm direct invasion of M. grandii by N. pyrausta, histological examinations were made of larval, pupal, and adult parasites, which were fixed in Carnoy’s solution, embedded in parafftn, sectioned at 6 pm, and stained with Heidenhain’s hematoxylin and eosin Y. Identification of the microsporidian in M. grandii and its host, 0. nubilalis, was initially determined from developmental stages stained with Giemsa (Hazard and Oldacre, 1975), and measurements of fresh living mature spores were made with an ocular micrometer at the light microscope level. Further life cycle comparisons and species verification were obtained at the ultrastructural level. Infected corn borer and parasite tissues were fixed in 2.5% glutaraldehyde, 1.0% acrolein in 0.1 M sodium cacodylate (PH 7.5), postfixed in 1.0% osmium tetroxide, dehydrated in an ethanol series, and embedded in a low-viscosity Spurr-Epon mixture (Ellis and Avery, 1978).
G.
ANDREADIS
RESULTS
Large numbers of N. pyrausta spores were observed within the midguts of emerging larvae and prepupae of M. grandii (Fig. 1). Infections were not seen in larval parasites developing within infected corn borers prior to their emergence from the host. Observations of pupae and surviving adults revealed direct systemic infections of midgut epithelial, fat body, muscle, nerve, and Malpighian tubule cells (Figs. 2-5). There was no sign of infection in gonadal tissue of either host sex. Giemsa-stained smears of infected parasite and corn borer tissues revealed indistinguishable developmental stages which were similar in appearance to those of N. pyrausta (see Hall, 1952; Kramer, 1959a). Mature spores from M. grandii (Fig. 6) measured (mean ? SE, n = 100) 4.23 + 0.06 pm x 1.75 ? 0.02 pm, and while slightly longer than those observed in the corn borer, 4.16 ? 0.06 pm x 1.76 ? 0.02 pm, did not differ significantly. No morphological differences between spores of N. pyrausta in M. grandii and 0. nubilalis were discernible at the ultrastructural level. The binucleate spores possessed a thin exospore, a large tightly compressed lamellate polaroplast, and a long uniformly thick polar filament consisting of lo- 12 coils (Fig. 7). N. pyrausta infections did not appear to adversely affect the ability of emerging larvae of M. grandii to pupate; however, adult emergence was significantly reduced by more than 38% (Table 1). Longevity of adult survivors of both sexes infected with N. pyrausta was significantly shorter than that recorded for uninfected controls (Table 2).
Parasitism of corn borer larvae by M. grandii was 9.2% (n = 704). N. pyrausta was found infecting 53.8% of these parasites (n = 1697) and when present was observed in all individuals obtained from a single corn borer host. The prevalence of infection in M. grandii did not differ significantly from the 56.7% prevalence of N. pyrausta in nonparasitized corn borers (n = 639).
which develop within N. pyrausta-infected corn borer larvae are clearly susceptible to the microsporidian pathogen. Infections appear to be initiated when spores, contained within corn borer Malpighian tubules, are ingested by larval parasites at the time of emergence from the body of the host. Parker (1931) has shown larval feeding prior to emergence to exclude
DISCUSSION M. grandii
N. pyrausta
INFECTION
IN
M. grandii
FIG. 1. Section through the midgut (Mg) of a Macrocentrus grandii prepupa showing ingested spores of Nosema pyrausta (Np). x950. FIG. 2-5. Tissues of pupal and adult Macrocentrus grandii infected with Mosema pyrausta (Np). FIG. 2. Midgut epithelial ceils (Mep). x950. FIG. 3. Adipose tissue. x700. FIG. 4. Abdominal nerve ganglion (NG). x500. FIG. 5. Thoracic musculature (MS). x830. FIG. 6. Mature spores of Nosema pyrausra from Macrocentrus grandii, phase contrast. x 3 100.
231
232
THEODORE
G. ANDREADIS
7 -
PF
EN FIG. 7. Electron micrograph of a mature spore of Nosema pyrausta from Macrocentrus grandii. AD, anchoring disk; CM, cytoplasmic membrane; EN, endospore; EX, exospore; Mnb, manubroid part of the polar filament; N,, N,, nuclei; P, polaroplast; PF, polar filament. ~40,000.
these host tissues. Direct systemic infections result, which rapidly spread throughout the body of the parasite and adversely affect pupal development and adult longevity. Infected female M. grandii are seemingly unable to transmit the pathogen to additional corn borer hosts since they die before completing the minimum preovipositional period of 3-4 days (Parker, 1931). Development of N. pyrausta in M. grundii appears to be identical to that which occurs in its primary host. Mature spores show no morphological differences in size
or shape as have been reported for other host-parasite-pathogen interrelationships (Brooks and Cranford, 1972). Since the prevalence of infection in parasite populations closely parallels that observed in the corn borer host, N. pyrausta may play a significant role in limiting or preventing the establishment of populations of M. grandii, especially when corn borer infection levels with N. pyrausta are high as is commonly the case (Kramer, 1959b; Van Denburgh and Burbutis, 1962; Peairs and TABLE
2
ADULTLONGEVITYOFUNINFECTEDAND Nosema pyraUSfa-INFECTED Macrocentrus
TABLE
1
NUMBEROF UNINFECTED AND NosemapyraustaINFECTED Macrocentrus grandii COMPLETING EACH DEVELOPMENTAL STAGE
Infected
Larvae Pupae Adults
Uninfected
No.
%
No.
%
821 762 377
92.8 45.9”
876 819 738
93.5 84.2
fl Significantly lower than uninfected % (P < 0.01).
No. of individuals
grandii
Mean f SD (days)
Range
Male Infected Uninfected
159 246
2.3 f 0.9” 14.3 k 2.7
1-4 2-25
Female Infected Uninfected
218 492
1.9 t 0.5” 16.6 _’ 2.6
l-3 3-25
‘I Significantly 0.01).
lower than uninfected
mean (P i
N. pyrausta
INFECTION
IN
M. grandii
233
of Microspotidia (Protozoa) close to Thelohania, Lilly, 1974; Hill and Gray, 1979). Hill et al. with descriptions of one new family, eight new gen(1978) felt N. pyrausta may have been a era and thirteen new species. U.S. Dep. Agr. Tech. factor in the decline and disappearance of Bull., 1530. the tachinid parasite Lydella thompsoni in HILL, R. E., CARPINO, D. P., AND MAYO, Z. B. 1978. certain areas of Nebraska. Although it is Insect parasites of the European corn borer Ostrinia generally believed that introductions of N. nubi/alis in Nebraska from 1948-1976. Environ. Entomol., 7, 249-253. pyrausta into large segments of corn borer populations would have a major suppres- HILL, R. E., AND GRAY, W. J. 1979. Effects of the microsporidium, Nosema pyrausta, on field populasive effect on that pest (Lewis and Lynch, tions of European corn borers in Nebraska. Environ. 1976), results obtained in this study indicate -Entomol., 8, 91-95. it may also reduce the effectiveness of other KRAMER, J. P. 1959a. Studies on the life history of Perezia pyraustae Paillot (Microsporidia: natural control agents. Therefore, it would ‘. Nosematidae). Trans. Amer. Microsc. Sot., 78, seem imperative to consider the relative 336-342. importance of each before initiating such a KRAMER, J. P. 1959b. Observations on the seasonal program. incidence of microsporidiosis in European corn
REFERENCES BAKER, W. A. 1958. Parasites of the European corn borer in the United States. In “Proceedings, 10th International Congress of Entomology, Montreal, 1956,” Vol. 4, pp. 487-492. BROOKS, W. M. 1973. Protozoa: Host-parasitepathogen interrelationships. Misc. Pub. Entomol. Sot. Amer., 9, 105-111. BROOKS, W. M., AND CRANFORD, J. D. 1972. Microsporidiosis of the hymenopterous parasites, Campoletis sonorensis and Cardiochiles nigriceps, larval parasites of Heliothis species. J. Invertebr. Pathol., 20, 77-94. ELLIS, E. A., AND AVERY, S. W. 1978. Resin formulations incorporating Epon 812 into a low viscosity embedding medium. Southeast Electron Microsc. Sot. Proc., 1, 20. HALL, I. M. 1952. Observations on Perezia pyraustae Paillot, a microsporidian parasite of the European corn borer. J. Parasitol., 38, 48-52. HAZARD, E. I., AND OLDACRE, S. W. 1975. Revision
borer populations in Illinois. Entomophaga, 4, 31-42. LEWIS, L. C., AND LYNCH, R. E. 1976. Influence on the European corn borer of Nosema pyrausta and resistance in maize to leaf feeding. Environ. Entomol., 5, 139-142. PARKER, H. L. 1931. Macrocentrus gifuensis Ashmead, a polyembryonic braconid parasite in the European corn borer. U.S. Dep. Agr. Tech. Bull., 230. PEAIRS, F. B., AND LILLY, J. H. 1974. Nosema pyrausta in populations of the European corn borer, Ostrinia nubilalis, in Massachusetts. Environ. Entomol.,
3, 878-879.
VAN DENBURGH, R. S., AND BURBUTIS, P. P. 1962. The host-parasite relationship of the European corn borer, Ostrinia nubilalis, and the protozoan, Perezia pyraustae, in Delaware. 1. Econ. Entomol., 55, 65-67. YORK, G. T. 1961. Microsporidia in parasites of the European corn borer. J. Insect Pathol., 3, lOl- 102.
OF INVERTEBRATE
PATHOLOGY
35,229-233
(1980)
Noserna pyrausta Infection in Macrocentrus grandii, a Braconid Parasite of the European Corn Borer, Ostrinia nubilalis THEODOREG.ANDREADIS Department
of Entomology,
Connecticut
Agricultural
Experiment
Station,
New
Haven,
Connecricur
06504
Received May 29, 1979 Macrocentrus grandii which develop within Nosema pyrausta-infected larvae of the European corn borer, Ostrinin nubilalis, develop direct systemic infections from the ingestion of spores at the time of larval emergence from the host. Infections adversely affect pupal development and adult longevity. Infected females are unable to transmit the microsporidian to additional corn borer hosts. Pathogen development in the parasite host appears identical to its development in the corn borer host and mature spores show no morphological differences in size or shape when observed at the ultrastructural level. The prevalence of infection in natural parasite populations is 53.8% and closely parallels the 56.7% prevalence of infection in corn borer populations. Results suggest N. pyrausra may play a significant role in limiting M. grandii populations when levels ofN. pyrausta in corn borers are high. KEY WORDS: Nosema pyrausta; Macrocenrrus grandii; Ostrinia nubilalis; natural infections; development; survival; longevity.
INTRODUCTION
The susceptibility of insect parasites to microsporidian pathogens of their hosts is well known and has been reviewed (Brooks, 1973). In most instances, parasites which develop within infected hosts fail to mature, or if they do, develop into weak adults which are short lived and exhibit reduced fecundity. These detrimental effects generally result from the direct infection of the parasite by the pathogen but may also occur when large numbers of ingested spores accumulate in the parasite’s midgut. When direct invasion does occur, pathogen development within parasitic hosts has been shown to be similar to that which occurs in its normal host, but may result in changes in spore size (Brooks and Cranford, 1972). In 1926, a polyembryonic braconid parasite, Macrocentrus grandii, was introduced into North America for control of the European corn borer, Ostrinia nubilalis. It became the predominant parasite of the corn borer in Connecticut, but the prevalence of parasitism never exceeded 28% (Baker, 1958) and its inability to reduce corn borer populations significantly was never com-
pletely understood. During laboratory rearing of M. grandii, York (1961) observed mortality in the parasites prior to pupation. Although no details were provided, he attributed this to infection by Nosema pyrausta, a well-known and widespread microsporidian pathogen of the corn borer host. This study was undertaken to identify and investigate the development of this microsporidian pathogen in M. grandii, to quantify its effects upon the host, and to determine its prevalence in natural parasite populations. MATERIALS
AND METHODS
Healthy and N. pyrausta-infected M. grandii were obtained from mature European corn borer larvae collected at Lockwood Farm in Hamden, Connecticut, during October and November 1978. Corn borer larvae were isolated in 1-oz plastic containers supplied with corrugated cardboard squares and moist filter paper disks to maintain high humidity, held. at 25°C under constant light, and examined daily for larval emergence of M. grandii. Records were kept of the number of M. grandii larvae, pupae, and adults obtained 229 0022-201 l/80/030229-05501.00 Copyright All rights
0 1980 by Academic Press, Inc. of reproduction in any form reserved.
230
THEODORE
from each corn borer host. Sibling adult parasites (obtained from a single host) were collectively transferred to l-pint screened paper containers supplied with plain water and honey and maintained at 25”C, relative humidity 75-80% under an 18-hr photoperiod. Adult mortality was recorded daily. N. pyrausta infection in M. grandii was determined by direct examination of tissues for spores under phase-contrast microscopy following death of the parasite. Nonparasitized corn borer larvae were held until adult emergence or death and then examined for N. pyrausta and larval parasites which may have failed to develop. To confirm direct invasion of M. grandii by N. pyrausta, histological examinations were made of larval, pupal, and adult parasites, which were fixed in Carnoy’s solution, embedded in parafftn, sectioned at 6 pm, and stained with Heidenhain’s hematoxylin and eosin Y. Identification of the microsporidian in M. grandii and its host, 0. nubilalis, was initially determined from developmental stages stained with Giemsa (Hazard and Oldacre, 1975), and measurements of fresh living mature spores were made with an ocular micrometer at the light microscope level. Further life cycle comparisons and species verification were obtained at the ultrastructural level. Infected corn borer and parasite tissues were fixed in 2.5% glutaraldehyde, 1.0% acrolein in 0.1 M sodium cacodylate (PH 7.5), postfixed in 1.0% osmium tetroxide, dehydrated in an ethanol series, and embedded in a low-viscosity Spurr-Epon mixture (Ellis and Avery, 1978).
G.
ANDREADIS
RESULTS
Large numbers of N. pyrausta spores were observed within the midguts of emerging larvae and prepupae of M. grandii (Fig. 1). Infections were not seen in larval parasites developing within infected corn borers prior to their emergence from the host. Observations of pupae and surviving adults revealed direct systemic infections of midgut epithelial, fat body, muscle, nerve, and Malpighian tubule cells (Figs. 2-5). There was no sign of infection in gonadal tissue of either host sex. Giemsa-stained smears of infected parasite and corn borer tissues revealed indistinguishable developmental stages which were similar in appearance to those of N. pyrausta (see Hall, 1952; Kramer, 1959a). Mature spores from M. grandii (Fig. 6) measured (mean ? SE, n = 100) 4.23 + 0.06 pm x 1.75 ? 0.02 pm, and while slightly longer than those observed in the corn borer, 4.16 ? 0.06 pm x 1.76 ? 0.02 pm, did not differ significantly. No morphological differences between spores of N. pyrausta in M. grandii and 0. nubilalis were discernible at the ultrastructural level. The binucleate spores possessed a thin exospore, a large tightly compressed lamellate polaroplast, and a long uniformly thick polar filament consisting of lo- 12 coils (Fig. 7). N. pyrausta infections did not appear to adversely affect the ability of emerging larvae of M. grandii to pupate; however, adult emergence was significantly reduced by more than 38% (Table 1). Longevity of adult survivors of both sexes infected with N. pyrausta was significantly shorter than that recorded for uninfected controls (Table 2).
Parasitism of corn borer larvae by M. grandii was 9.2% (n = 704). N. pyrausta was found infecting 53.8% of these parasites (n = 1697) and when present was observed in all individuals obtained from a single corn borer host. The prevalence of infection in M. grandii did not differ significantly from the 56.7% prevalence of N. pyrausta in nonparasitized corn borers (n = 639).
which develop within N. pyrausta-infected corn borer larvae are clearly susceptible to the microsporidian pathogen. Infections appear to be initiated when spores, contained within corn borer Malpighian tubules, are ingested by larval parasites at the time of emergence from the body of the host. Parker (1931) has shown larval feeding prior to emergence to exclude
DISCUSSION M. grandii
N. pyrausta
INFECTION
IN
M. grandii
FIG. 1. Section through the midgut (Mg) of a Macrocentrus grandii prepupa showing ingested spores of Nosema pyrausta (Np). x950. FIG. 2-5. Tissues of pupal and adult Macrocentrus grandii infected with Mosema pyrausta (Np). FIG. 2. Midgut epithelial ceils (Mep). x950. FIG. 3. Adipose tissue. x700. FIG. 4. Abdominal nerve ganglion (NG). x500. FIG. 5. Thoracic musculature (MS). x830. FIG. 6. Mature spores of Nosema pyrausra from Macrocentrus grandii, phase contrast. x 3 100.
231
232
THEODORE
G. ANDREADIS
7 -
PF
EN FIG. 7. Electron micrograph of a mature spore of Nosema pyrausta from Macrocentrus grandii. AD, anchoring disk; CM, cytoplasmic membrane; EN, endospore; EX, exospore; Mnb, manubroid part of the polar filament; N,, N,, nuclei; P, polaroplast; PF, polar filament. ~40,000.
these host tissues. Direct systemic infections result, which rapidly spread throughout the body of the parasite and adversely affect pupal development and adult longevity. Infected female M. grandii are seemingly unable to transmit the pathogen to additional corn borer hosts since they die before completing the minimum preovipositional period of 3-4 days (Parker, 1931). Development of N. pyrausta in M. grundii appears to be identical to that which occurs in its primary host. Mature spores show no morphological differences in size
or shape as have been reported for other host-parasite-pathogen interrelationships (Brooks and Cranford, 1972). Since the prevalence of infection in parasite populations closely parallels that observed in the corn borer host, N. pyrausta may play a significant role in limiting or preventing the establishment of populations of M. grandii, especially when corn borer infection levels with N. pyrausta are high as is commonly the case (Kramer, 1959b; Van Denburgh and Burbutis, 1962; Peairs and TABLE
2
ADULTLONGEVITYOFUNINFECTEDAND Nosema pyraUSfa-INFECTED Macrocentrus
TABLE
1
NUMBEROF UNINFECTED AND NosemapyraustaINFECTED Macrocentrus grandii COMPLETING EACH DEVELOPMENTAL STAGE
Infected
Larvae Pupae Adults
Uninfected
No.
%
No.
%
821 762 377
92.8 45.9”
876 819 738
93.5 84.2
fl Significantly lower than uninfected % (P < 0.01).
No. of individuals
grandii
Mean f SD (days)
Range
Male Infected Uninfected
159 246
2.3 f 0.9” 14.3 k 2.7
1-4 2-25
Female Infected Uninfected
218 492
1.9 t 0.5” 16.6 _’ 2.6
l-3 3-25
‘I Significantly 0.01).
lower than uninfected
mean (P i
N. pyrausta
INFECTION
IN
M. grandii
233
of Microspotidia (Protozoa) close to Thelohania, Lilly, 1974; Hill and Gray, 1979). Hill et al. with descriptions of one new family, eight new gen(1978) felt N. pyrausta may have been a era and thirteen new species. U.S. Dep. Agr. Tech. factor in the decline and disappearance of Bull., 1530. the tachinid parasite Lydella thompsoni in HILL, R. E., CARPINO, D. P., AND MAYO, Z. B. 1978. certain areas of Nebraska. Although it is Insect parasites of the European corn borer Ostrinia generally believed that introductions of N. nubi/alis in Nebraska from 1948-1976. Environ. Entomol., 7, 249-253. pyrausta into large segments of corn borer populations would have a major suppres- HILL, R. E., AND GRAY, W. J. 1979. Effects of the microsporidium, Nosema pyrausta, on field populasive effect on that pest (Lewis and Lynch, tions of European corn borers in Nebraska. Environ. 1976), results obtained in this study indicate -Entomol., 8, 91-95. it may also reduce the effectiveness of other KRAMER, J. P. 1959a. Studies on the life history of Perezia pyraustae Paillot (Microsporidia: natural control agents. Therefore, it would ‘. Nosematidae). Trans. Amer. Microsc. Sot., 78, seem imperative to consider the relative 336-342. importance of each before initiating such a KRAMER, J. P. 1959b. Observations on the seasonal program. incidence of microsporidiosis in European corn
REFERENCES BAKER, W. A. 1958. Parasites of the European corn borer in the United States. In “Proceedings, 10th International Congress of Entomology, Montreal, 1956,” Vol. 4, pp. 487-492. BROOKS, W. M. 1973. Protozoa: Host-parasitepathogen interrelationships. Misc. Pub. Entomol. Sot. Amer., 9, 105-111. BROOKS, W. M., AND CRANFORD, J. D. 1972. Microsporidiosis of the hymenopterous parasites, Campoletis sonorensis and Cardiochiles nigriceps, larval parasites of Heliothis species. J. Invertebr. Pathol., 20, 77-94. ELLIS, E. A., AND AVERY, S. W. 1978. Resin formulations incorporating Epon 812 into a low viscosity embedding medium. Southeast Electron Microsc. Sot. Proc., 1, 20. HALL, I. M. 1952. Observations on Perezia pyraustae Paillot, a microsporidian parasite of the European corn borer. J. Parasitol., 38, 48-52. HAZARD, E. I., AND OLDACRE, S. W. 1975. Revision
borer populations in Illinois. Entomophaga, 4, 31-42. LEWIS, L. C., AND LYNCH, R. E. 1976. Influence on the European corn borer of Nosema pyrausta and resistance in maize to leaf feeding. Environ. Entomol., 5, 139-142. PARKER, H. L. 1931. Macrocentrus gifuensis Ashmead, a polyembryonic braconid parasite in the European corn borer. U.S. Dep. Agr. Tech. Bull., 230. PEAIRS, F. B., AND LILLY, J. H. 1974. Nosema pyrausta in populations of the European corn borer, Ostrinia nubilalis, in Massachusetts. Environ. Entomol.,
3, 878-879.
VAN DENBURGH, R. S., AND BURBUTIS, P. P. 1962. The host-parasite relationship of the European corn borer, Ostrinia nubilalis, and the protozoan, Perezia pyraustae, in Delaware. 1. Econ. Entomol., 55, 65-67. YORK, G. T. 1961. Microsporidia in parasites of the European corn borer. J. Insect Pathol., 3, lOl- 102.