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Host range studies of an Erynia radicans strain (Zygomycetes: Entomophthoraceae) isolated from Empoasca fabae (Homoptera: Cicadellidae)
JOURNAL
OF INVERTEBRATE
PATHOLOGY
50,
75-77
(1987)
Host Range Studies of an Erynia radicans Strain (Zygomycetes: Entomophthoraceae) Isolated from Empoasca fabae (Homoptera: Cicadellidae) Erynia radicans is a geographically and ecologically diverse fungal entomopathogen with a reported host range of many insect families in at least seven orders (B. Papierok, B. Valadlo L. Torres, and M. Arnault, Entomophaga 29, 109- 119, 1984). Individual strains of E. radicans may, however, have a more limited host range. B. Papierok et al. suggested that individual strains of E. radicans are evolutionarily adapted to infect taxonomically related insect hosts. This is very important in selecting E. radicans isolates for release as biological control agents of economically important insect pests (R. J. Milner, R. S. Soper, and G. G. Lutton, J. Aust. Entomol. Sot. 21, 113- 118, 1982). We describe the host range of an E. radicans strain isolated from the potato leafhopper, Empoasca fabae, in Wisconsin in October 1983. This isolate was subsequently deposited as ARSEF 1020 in the U.S. Department of Agriculture, ARS, Culture Collection at the Boyce Thompson Institute (Ithaca, NY). An isolate derived from one primary spore, obtained from an E. fabae nymph experimentally infected in the laboratory, was used in all experiments and was subcultured every 3-4 weeks (Sabouraud’s dextrose agar with 1% yeast extract, 20°C 16L:SD). With every 4th-5th subculture, the strain was passed through E. fabae and reisolated to maintain virulence. All insect species tested were acquired from colonies at the University of Illinois or the Illinois Natural History Survey. Lepidopterous larvae were reared on art&al diets; all other insects were reared on preferred host plants.
Plugs of E. radicans were removed from the edges of actively growing cultures with a cork borer (2 cm diam.) and placed in Petri dishes (3.5 cm diam.) containing 1.5% nonnutrient agar. Approximately 12 hr later, the fungus showered conidia at relatively high rates (estimated at 20 conidia/ min). At this time, insects were placed in the bottom of a Petri dish (3.5 cm diam.) containing a piece of host plant tissue (homopterous insects) or artificial diet (Lepidoptera). The Petri dish containing the plug of E. radicans was then inverted over the insects and the edges were sealed with Paratilm to maintain high humidity. Approximately 20 insects of each species were held in this manner at room temperature for a 17-hr inoculation period. Following the inoculation period, homopterous insects were placed in clean Petri dishes (sealed with Parafilm) containing excised host plant leaves, while lepidopterous larvae were placed in cups of fresh diet. All containers were then placed in a growth chamber (20°C 16L:SD). Containers were examined daily for the presence of dead insects. Cadavers were placed on 1.5% nonnutrient agar and held for several days to observe spore formation. Every insect was examined microscopically for conidiophore and/or resting spore development at the conclusion of the experiment. The LT,, was determined by counting the number of days between the day of inoculation and the day when at least 50% of the infected insects had died from mycosis. Of the 12 insect species tested, 5 were susceptible to the E. fabae isolate of E. ra75 0022-2011/87
$1.50
Copyright 0 1987 by Academic Press. Inc. All rights of reproduction in any form reserved.
NOTES
76
&cans (Table 1). Three leafhoppers, E. fabae, Empoasca kraemeri, and Circulifer tenellus, were the most susceptible (89, 78, and 89% infection, respectively). A fourth leafhopper species, Macrosteles fascifrons, was surprisingly not susceptible although it is in the same subfamily as Circulifer (D. M. DeLong, Bull. Ill. Nat. Hist. Surv. 24, 97-376, 1948). Because of their economic importance, E. fubae, C. tenellus, and M. fascifrons have been studied thoroughly during the last 60 years, but there are few reports of fungal pathogens in field populations of these insects. W. C. Cook (USDA Tech. Bull. 1365, 1967) and H. H. P. Severins (Hilgardia 7, 281-360, 1933) mentioned fungal pathogens of C. tenellus, but descriptions of infections were incomplete and identifications were not attempted. We believe that our report represents the first confirmed E. radicans infections in E. fabae and C. tenellus. E.
TABLE SUSCEFTIBILITYOFSEVERALINSECTSPECIESTOAN
kraemeri, a South American sibling species of E. fabae, is commonly infected by E. radicans (R. S. Soper, pers. commun.). Acrythosiphon pisum was not susceptible and Myzus persicae was only slightly susceptible (5% infection) to the E. fabae isolate of E. radicans. G. Thoizon (Ann. Sot. Entomol. Fr. 6, 517-562, 1970) listed A. pisum, the pea aphid, and M. persicae, the green peach aphid, as susceptible to E. radicans. B. Papierok, B. Valadao L.
Torres,
and M. Arnault
cit., 1984) to test the relative virulence of several strains of E. radicans isolated from different hosts and localities. Although mortality varied with respect to strain, A. pisum was susceptible to all strains. Aphis craccivora was not susceptible to our E. rudicans isolate, and no published information is available concerning the susceptibility of A. craccivora to E. radicans. R. Kenneth, G. Wallis, Y.
1 Empoascafabae
ISOLATEOF
No. inoculated
Life stageb
Erynia
radicans”
Number forming spore type
Order Family Species
(lot.
used A. pisum in the laboratory
No. infected
Conidia
Resting
Both
LTm (days)
Homoptera Cicadellidae Empoasca fabae Empoasca kraemeri’ Macrosteles fascifrons Circulifer tenellus
19 18 20 19
334 3,4 2-4 2-4
17 14 0 17
3 10 8
7 1 6
7 3 3
4 3 4
20 20 20 20
2,3,&W
2 0
1 0
-
2,3.A
4 0 0 I
I
2,3.A,W
5 8
20
122
0
-
-
-
-
20 20
1.2 1.2
0 0
-
-
-
-
20
12
0
-
-
-
-
Aphididae Rhopalosiphon maidis Aphis craccivora Acyrthosiphon pisum Myzus persicae
2.3AW
1
Lepidoptera Lymantriidae Lymantria
dispar
Noctuidae Spodoptera Trichopplusia
exigua ni
Pyralidae Galleria
mellonella
Q See text for methods of inoculation, holding, etc b Life stages of insects: numbers refer to larval or nymphal instar. A, apterous adult; W, winged adult c E. kraemeri was exposed to conidia for only 4 hr instead of the 17 hr reported for the other species.
77
NOTES
Olmert, and J. Halperin (Zsr. J. Agric. Res. 21, 63-66, 1971) and 1. Ben-Ze’ev, R. G. Kenneth, S. Bitton, and R. S. Soper (Phytoparasitica 12, 167-176, 1984) found several other Aphis species infected with E. radicans in field surveys. Rhopalosiphon maidis was slightly susceptible (20% infection) to the Wisconsin strain of E. radicans. This is apparently the first report of R. maidis as a host for E. radicans, although I. Ben-Ze’ev, R. G. Kenneth, S. Bitton, and R. S. Soper (lot. cit., 1984) found R. padi infected with E. radicans in Israel. None of the lepidopteran species we tested were susceptible to our isolate of E. radicans. To our knowledge these species have not been exposed to other E. radicans strains. Other lepidopterans such as Choristoneura fumiferana are susceptible to other strains of E. radicans (J. D. Vandenberg and R. S. Soper, J. N. Y. Entomol. Sot. 83, 254-255, 1975) and further testing may reveal that some Lepidoptera are susceptible to our isolate. There is a general concensus that E. radicans at the least is a very diverse species and may even be a complex of species. Our study confirms this view with respect to host range. Our strain of E. radicans was not infectious to one known aphid host (A. pisum) and was only mildly pathogenic to another (M. persicae). This suggests a
much different host range than strains that have been examined by other researchers. KEY WORDS: Empoasca fabae; Homoptera; Erynia radicans; fungus; host range. Funding for this project came from the Illinois Natural History Survey, the Illinois Agricultural Experiment Station, and from USDA Grant 82-CRSR-21000, Subc. L200044, The Development of Comprehensive, Unified, Economically and Environmentally Sound Systems of Integrated Pest Management of Alfalfa. We thank the BeaniCowpea Collaborative Research Support Program (CRSP) and the National Rice and Bean Research Center (CNPAF) in Goiania, Goias, Brazil, for providing laboratory space and equipment to M. R. McGuire for the work with E. kraemeri. We also thank K. W. O’Hayer and M. J. Morris for helpful comments on an earlier draft of this manuscript.
M. R. MCGUIRE~ J. V. MADDOX E. J. ARMBRUST Section of Economic Entomology Illinois National History Survey 607 East Peabody Champaign, Illinois 61820 Received December 8, 1986; accepted March II, 1987 i U.S. Department of Agriculture, ARS, Rangeland Insect Laboratory, Montana State University, Bozeman, MT 59717-0001.
OF INVERTEBRATE
PATHOLOGY
50,
75-77
(1987)
Host Range Studies of an Erynia radicans Strain (Zygomycetes: Entomophthoraceae) Isolated from Empoasca fabae (Homoptera: Cicadellidae) Erynia radicans is a geographically and ecologically diverse fungal entomopathogen with a reported host range of many insect families in at least seven orders (B. Papierok, B. Valadlo L. Torres, and M. Arnault, Entomophaga 29, 109- 119, 1984). Individual strains of E. radicans may, however, have a more limited host range. B. Papierok et al. suggested that individual strains of E. radicans are evolutionarily adapted to infect taxonomically related insect hosts. This is very important in selecting E. radicans isolates for release as biological control agents of economically important insect pests (R. J. Milner, R. S. Soper, and G. G. Lutton, J. Aust. Entomol. Sot. 21, 113- 118, 1982). We describe the host range of an E. radicans strain isolated from the potato leafhopper, Empoasca fabae, in Wisconsin in October 1983. This isolate was subsequently deposited as ARSEF 1020 in the U.S. Department of Agriculture, ARS, Culture Collection at the Boyce Thompson Institute (Ithaca, NY). An isolate derived from one primary spore, obtained from an E. fabae nymph experimentally infected in the laboratory, was used in all experiments and was subcultured every 3-4 weeks (Sabouraud’s dextrose agar with 1% yeast extract, 20°C 16L:SD). With every 4th-5th subculture, the strain was passed through E. fabae and reisolated to maintain virulence. All insect species tested were acquired from colonies at the University of Illinois or the Illinois Natural History Survey. Lepidopterous larvae were reared on art&al diets; all other insects were reared on preferred host plants.
Plugs of E. radicans were removed from the edges of actively growing cultures with a cork borer (2 cm diam.) and placed in Petri dishes (3.5 cm diam.) containing 1.5% nonnutrient agar. Approximately 12 hr later, the fungus showered conidia at relatively high rates (estimated at 20 conidia/ min). At this time, insects were placed in the bottom of a Petri dish (3.5 cm diam.) containing a piece of host plant tissue (homopterous insects) or artificial diet (Lepidoptera). The Petri dish containing the plug of E. radicans was then inverted over the insects and the edges were sealed with Paratilm to maintain high humidity. Approximately 20 insects of each species were held in this manner at room temperature for a 17-hr inoculation period. Following the inoculation period, homopterous insects were placed in clean Petri dishes (sealed with Parafilm) containing excised host plant leaves, while lepidopterous larvae were placed in cups of fresh diet. All containers were then placed in a growth chamber (20°C 16L:SD). Containers were examined daily for the presence of dead insects. Cadavers were placed on 1.5% nonnutrient agar and held for several days to observe spore formation. Every insect was examined microscopically for conidiophore and/or resting spore development at the conclusion of the experiment. The LT,, was determined by counting the number of days between the day of inoculation and the day when at least 50% of the infected insects had died from mycosis. Of the 12 insect species tested, 5 were susceptible to the E. fabae isolate of E. ra75 0022-2011/87
$1.50
Copyright 0 1987 by Academic Press. Inc. All rights of reproduction in any form reserved.
NOTES
76
&cans (Table 1). Three leafhoppers, E. fabae, Empoasca kraemeri, and Circulifer tenellus, were the most susceptible (89, 78, and 89% infection, respectively). A fourth leafhopper species, Macrosteles fascifrons, was surprisingly not susceptible although it is in the same subfamily as Circulifer (D. M. DeLong, Bull. Ill. Nat. Hist. Surv. 24, 97-376, 1948). Because of their economic importance, E. fubae, C. tenellus, and M. fascifrons have been studied thoroughly during the last 60 years, but there are few reports of fungal pathogens in field populations of these insects. W. C. Cook (USDA Tech. Bull. 1365, 1967) and H. H. P. Severins (Hilgardia 7, 281-360, 1933) mentioned fungal pathogens of C. tenellus, but descriptions of infections were incomplete and identifications were not attempted. We believe that our report represents the first confirmed E. radicans infections in E. fabae and C. tenellus. E.
TABLE SUSCEFTIBILITYOFSEVERALINSECTSPECIESTOAN
kraemeri, a South American sibling species of E. fabae, is commonly infected by E. radicans (R. S. Soper, pers. commun.). Acrythosiphon pisum was not susceptible and Myzus persicae was only slightly susceptible (5% infection) to the E. fabae isolate of E. radicans. G. Thoizon (Ann. Sot. Entomol. Fr. 6, 517-562, 1970) listed A. pisum, the pea aphid, and M. persicae, the green peach aphid, as susceptible to E. radicans. B. Papierok, B. Valadao L.
Torres,
and M. Arnault
cit., 1984) to test the relative virulence of several strains of E. radicans isolated from different hosts and localities. Although mortality varied with respect to strain, A. pisum was susceptible to all strains. Aphis craccivora was not susceptible to our E. rudicans isolate, and no published information is available concerning the susceptibility of A. craccivora to E. radicans. R. Kenneth, G. Wallis, Y.
1 Empoascafabae
ISOLATEOF
No. inoculated
Life stageb
Erynia
radicans”
Number forming spore type
Order Family Species
(lot.
used A. pisum in the laboratory
No. infected
Conidia
Resting
Both
LTm (days)
Homoptera Cicadellidae Empoasca fabae Empoasca kraemeri’ Macrosteles fascifrons Circulifer tenellus
19 18 20 19
334 3,4 2-4 2-4
17 14 0 17
3 10 8
7 1 6
7 3 3
4 3 4
20 20 20 20
2,3,&W
2 0
1 0
-
2,3.A
4 0 0 I
I
2,3.A,W
5 8
20
122
0
-
-
-
-
20 20
1.2 1.2
0 0
-
-
-
-
20
12
0
-
-
-
-
Aphididae Rhopalosiphon maidis Aphis craccivora Acyrthosiphon pisum Myzus persicae
2.3AW
1
Lepidoptera Lymantriidae Lymantria
dispar
Noctuidae Spodoptera Trichopplusia
exigua ni
Pyralidae Galleria
mellonella
Q See text for methods of inoculation, holding, etc b Life stages of insects: numbers refer to larval or nymphal instar. A, apterous adult; W, winged adult c E. kraemeri was exposed to conidia for only 4 hr instead of the 17 hr reported for the other species.
77
NOTES
Olmert, and J. Halperin (Zsr. J. Agric. Res. 21, 63-66, 1971) and 1. Ben-Ze’ev, R. G. Kenneth, S. Bitton, and R. S. Soper (Phytoparasitica 12, 167-176, 1984) found several other Aphis species infected with E. radicans in field surveys. Rhopalosiphon maidis was slightly susceptible (20% infection) to the Wisconsin strain of E. radicans. This is apparently the first report of R. maidis as a host for E. radicans, although I. Ben-Ze’ev, R. G. Kenneth, S. Bitton, and R. S. Soper (lot. cit., 1984) found R. padi infected with E. radicans in Israel. None of the lepidopteran species we tested were susceptible to our isolate of E. radicans. To our knowledge these species have not been exposed to other E. radicans strains. Other lepidopterans such as Choristoneura fumiferana are susceptible to other strains of E. radicans (J. D. Vandenberg and R. S. Soper, J. N. Y. Entomol. Sot. 83, 254-255, 1975) and further testing may reveal that some Lepidoptera are susceptible to our isolate. There is a general concensus that E. radicans at the least is a very diverse species and may even be a complex of species. Our study confirms this view with respect to host range. Our strain of E. radicans was not infectious to one known aphid host (A. pisum) and was only mildly pathogenic to another (M. persicae). This suggests a
much different host range than strains that have been examined by other researchers. KEY WORDS: Empoasca fabae; Homoptera; Erynia radicans; fungus; host range. Funding for this project came from the Illinois Natural History Survey, the Illinois Agricultural Experiment Station, and from USDA Grant 82-CRSR-21000, Subc. L200044, The Development of Comprehensive, Unified, Economically and Environmentally Sound Systems of Integrated Pest Management of Alfalfa. We thank the BeaniCowpea Collaborative Research Support Program (CRSP) and the National Rice and Bean Research Center (CNPAF) in Goiania, Goias, Brazil, for providing laboratory space and equipment to M. R. McGuire for the work with E. kraemeri. We also thank K. W. O’Hayer and M. J. Morris for helpful comments on an earlier draft of this manuscript.
M. R. MCGUIRE~ J. V. MADDOX E. J. ARMBRUST Section of Economic Entomology Illinois National History Survey 607 East Peabody Champaign, Illinois 61820 Received December 8, 1986; accepted March II, 1987 i U.S. Department of Agriculture, ARS, Rangeland Insect Laboratory, Montana State University, Bozeman, MT 59717-0001.