The braconid parasitoid Microctonus colesi was released in Story and Boone counties, Iowa, but not recovered from collected alfalfa weevils, Hypera postica. Sampled adult weevils were parasitized at an overall seasonal rate of 41.5% by Microctonus aethiopoides, although it had not been released in the immediate vicinity

Mertins, James W

English

ValpoScholar

The Great Lakes Entomologist 
Volume 17 
Number 4 - Winter 1984 Number 4 - Winter 
1984 
Article 10 
December 1984 
Notes on Microctonus Spp. (Hymenoptera: Braconidae) 
Introduced to Iowa Against the Alfalfa Weevil, Hypera Postica 
(Coleoptera: Curculionidae) 
James W. Mertins 
Iowa State University 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Mertins, James W. 1984. "Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced to Iowa 
Against the Alfalfa Weevil, Hypera Postica (Coleoptera: Curculionidae)," The Great Lakes Entomologist, vol 
17 (4) 
Available at: https://scholar.valpo.edu/tgle/vol17/iss4/10 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
1984 THE GREAT LAKES ENTOMOLOGIST 233 
NOTES ON MICROCTONUS SPP. (HYMENOPTERA: BRACONIDAE) 

INTRODUCED TO IOWA AGAINST THE ALFALFA WEEVIL, 

HYPERA POSTICA (COLEOPTERA: CURCULIONIDAE)1 

James W. Mertins2 
ABSTRACT 
The braconid parasitoid Microctonus colesi was released in Story and Boone counties, 
Iowa, but not recovered from collected alfalfa weevils, Hypera postica. Sampled adult 
weevils were parasitized at an overall seasonal rate of 41.5% by Microctonus 
aethiopoides, although it had not been released in the immediate vicinity. 
On 24 September 1981, I released 503 living adult Hypera postica (Gyllenhal) that 
came to me from Ohio. These weevils had been exposed in the laboratory as larvae to 
attack by female Microctonus colesi Drea, and ca. 60% of them should have contained 
immature M. colesi (pel's. comm., J. K. Flessel, Ohio Agricultural Research and De­
velopment Center, Wooster). The weevils were released in 17 alfalfa fields in Boone and 
Story counties, Iowa, at the recommended rate of 25-50 weevils per field. 
The univoltine life cycle of thelyotokous M. colesi includes emergence of the mature 
larva from the adult host in the spring, when weevils resume activity and reenter alfalfa 
fields. Therefore, the most appropriate time to attempt recovery of progeny from the 
released parasitoids was spring 1983 (Dysart and Day 1976). Between 12 May and 13 
June 1983, I attempted to visit each release site once per week and to sweep-sample adult 
weevils for observation of parasitoid presence. Two of the original 17 fields had been 
converted to cornfields in the intervening year, and one additional field was treated with 
herbicide just before I attempted the sample in 1983. A fourth field was plowed after I 
took my first (and only) sample. 
During the 4.5 weeks of sampling, I collected and held for observation a total f 1346 
adult alfalfa weevils from the 14 alfalfa fields visited, taking a minimal sample of 30 and a 
maximum of 77 weevils/field/season. No M. c lesi were reared. Fortuitously, however, 
528 individuals of another exotic parasitoid, Microctonus aethiopoides Loan, emerged 
from the collected weevils, a seasonal parasitization rate of 41.5%. 
Microctonus aethiopoides occurred in every sampled field. although parasitized 
weevils were not present on every sampling date in every field. For example. no para­
sitoids emerged from the small number (51) of weevils collected from four fields before 
23 
May; similarly, a few weevils (19) collected from eight fields after 8 June produced 
only two parasitoids. The seasonal rates of parasitization by field ranged from 8.7% (in 
the field where only one early sample was possible) to 63.3% (in the field that produced 
only 30 adult weevils during the season). The earliest date of collection for parasitized 
weevils was 
23 May (seven of seven fields positive); the latest date was 13 June. Samples 
taken between 31 May and 3 June seemed to include weevils most likely to produce 
parasitoids. A 31 May sample of eight weevils from field 5 was 100% parasitized; 19 
weevils taken on the same day from field 1 were 85.3% parasitized, and 17 from field 14 
on 1 June were 85.0% attacked. 
'Journal Paper No. J-1I302 of the Iowa Agriculture and Home Economics Experiment Station, 
Ames, I  50011. Project No. 2558. 
2Department of Entomology, Iowa State University, Ames, IA 50011. 
1
Mertins: Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced to
Published by ValpoScholar, 1984
234 THE GREAT LAKES ENTOMOLOGIST Vol. 17, No.4 
The omnipresence of and high rates of attack by M. aethiopoides are all the more 
remarkable when one realizes that (to my knowledge) it had not been released in any of 
the study areas. The first Iowa release of M. aethiopoides was in distant Lee County in 
1975 (pers. comm., J. R. DeWitt, Department of Entomology, Iowa Stale University), 
but none was ever recovered there. The first Iowa specimens were collected in five other 
eastern counties in 1980 (USDA 1980l. The nearest release (one of d z ns in the current 
USDA parasitoid redistribution progr~rn) was in 1981 in Lafayette Township, northeast, 
but adjacent to the study areas. 
Microctollus colesi (to my knowledge) was never released in Iowa before this effort, 
but it was collecled from at least two southwestern counties as early as 1981 (unpublished 
report, USDA, APHIS, PPQ, Niles, MI). What has become of M. colesi in the release 
sites·J I do not know. But M. aethiopoides often has been associated in the past with 
suppression of alfalfa weevil populations (Dysart and Day 1976), and its great success in 
penetrating the central Iowa infestation is sufficient cause for optimism. 
ACKNOWLEDGMENT 
I appreciate the assistance of Dan Burden in the field and laboratory work reported 
here. 
LITERATURE CITED 
Dysart, R. 1., nd W. H. Day. 1976. Release and recovery of introduced parasites of the 
alfalfa weevil in eastern North America. USDA, Agric. Res. Serv., Prod. Res. Rep. 
167. 
USDA. 1980. Animal and Plant Health Inspection Service, Plant Protection and Quar­
antine. Coop. Plant Pest Rep. 5:564. 
2
The Great Lakes Entomologist, Vol. 17, No. 4 [1984], Art. 10
https://scholar.valpo.edu/tgle/vol17/iss4/10


Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced to Iowa Against the Alfalfa Weevil, Hypera Postica (Coleoptera: Curculionidae)

Valparaiso University

The Great Lakes Entomologist Volume 17 Number 4 - Winter 1984 Number 4 - Winter 1984 Article 10 December 1984 Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced to Iowa Against the Alfalfa Weevil, Hypera Postica (Coleoptera: Curculionidae) James W. Mertins Iowa State University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Mertins, James W. 1984. "Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced to Iowa Against the Alfalfa Weevil, Hypera Postica (Coleoptera: Curculionidae)," The Great Lakes Entomologist, vol 17 (4) Available at: https://scholar.valpo.edu/tgle/vol17/iss4/10 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1984 THE GREAT LAKES ENTOMOLOGIST 233 NOTES ON MICROCTONUS SPP. (HYMENOPTERA: BRACONIDAE) INTRODUCED TO IOWA AGAINST THE ALFALFA WEEVIL, HYPERA POSTICA (COLEOPTERA: CURCULIONIDAE)1 James W. Mertins2 ABSTRACT The braconid parasitoid Microctonus colesi was released in Story and Boone counties, Iowa, but not recovered from collected alfalfa weevils, Hypera postica. Sampled adult weevils were parasitized at an overall seasonal rate of 41.5% by Microctonus aethiopoides, although it had not been released in the immediate vicinity. On 24 September 1981, I released 503 living adult Hypera postica (Gyllenhal) that came to me from Ohio. These weevils had been exposed in the laboratory as larvae to attack by female Microctonus colesi Drea, and ca. 60% of them should have contained immature M. colesi (pel's. comm., J. K. Flessel, Ohio Agricultural Research and De­velopment Center, Wooster). The weevils were released in 17 alfalfa fields in Boone and Story counties, Iowa, at the recommended rate of 25-50 weevils per field. The univoltine life cycle of thelyotokous M. colesi includes emergence of the mature larva from the adult host in the spring, when weevils resume activity and reenter alfalfa fields. Therefore, the most appropriate time to attempt recovery of progeny from the released parasitoids was spring 1983 (Dysart and Day 1976). Between 12 May and 13 June 1983, I attempted to visit each release site once per week and to sweep-sample adult weevils for observation of parasitoid presence. Two of the original 17 fields had been converted to cornfields in the intervening year, and one additional field was treated with herbicide just before I attempted the sample in 1983. A fourth field was plowed after I took my first (and only) sample. During the 4.5 weeks of sampling, I collected and held for observation a total f 1346 adult alfalfa weevils from the 14 alfalfa fields visited, taking a minimal sample of 30 and a maximum of 77 weevils/field/season. No M. c lesi were reared. Fortuitously, however, 528 individuals of another exotic parasitoid, Microctonus aethiopoides Loan, emerged from the collected weevils, a seasonal parasitization rate of 41.5%. Microctonus aethiopoides occurred in every sampled field. although parasitized weevils were not present on every sampling date in every field. For example. no para­sitoids emerged from the small number (51) of weevils collected from four fields before 23 May; similarly, a few weevils (19) collected from eight fields after 8 June produced only two parasitoids. The seasonal rates of parasitization by field ranged from 8.7% (in the field where only one early sample was possible) to 63.3% (in the field that produced only 30 adult weevils during the season). The earliest date of collection for parasitized weevils was 23 May (seven of seven fields positive); the latest date was 13 June. Samples taken between 31 May and 3 June seemed to include weevils most likely to produce parasitoids. A 31 May sample of eight weevils from field 5 was 100% parasitized; 19 weevils taken on the same day from field 1 were 85.3% parasitized, and 17 from field 14 on 1 June were 85.0% attacked. 'Journal Paper No. J-1I302 of the Iowa Agriculture and Home Economics Experiment Station, Ames, I  50011. Project No. 2558. 2Department of Entomology, Iowa State University, Ames, IA 50011. 1Mertins: Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced toPublished by ValpoScholar, 1984234 THE GREAT LAKES ENTOMOLOGIST Vol. 17, No.4 The omnipresence of and high rates of attack by M. aethiopoides are all the more remarkable when one realizes that (to my knowledge) it had not been released in any of the study areas. The first Iowa release of M. aethiopoides was in distant Lee County in 1975 (pers. comm., J. R. DeWitt, Department of Entomology, Iowa Stale University), but none was ever recovered there. The first Iowa specimens were collected in five other eastern counties in 1980 (USDA 1980l. The nearest release (one of d z ns in the current USDA parasitoid redistribution progr~rn) was in 1981 in Lafayette Township, northeast, but adjacent to the study areas. Microctollus colesi (to my knowledge) was never released in Iowa before this effort, but it was collecled from at least two southwestern counties as early as 1981 (unpublished report, USDA, APHIS, PPQ, Niles, MI). What has become of M. colesi in the release sites·J I do not know. But M. aethiopoides often has been associated in the past with suppression of alfalfa weevil populations (Dysart and Day 1976), and its great success in penetrating the central Iowa infestation is sufficient cause for optimism. ACKNOWLEDGMENT I appreciate the assistance of Dan Burden in the field and laboratory work reported here. LITERATURE CITED Dysart, R. 1., nd W. H. Day. 1976. Release and recovery of introduced parasites of the alfalfa weevil in eastern North America. USDA, Agric. Res. Serv., Prod. Res. Rep. 167. USDA. 1980. Animal and Plant Health Inspection Service, Plant Protection and Quar­antine. Coop. Plant Pest Rep. 5:564. 2The Great Lakes Entomologist, Vol. 17, No. 4 [1984], Art. 10https://scholar.valpo.edu/tgle/vol17/iss4/10

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Notes on Microctonus Spp. (Hymenoptera: Braconidae) Introduced to Iowa Against the Alfalfa Weevil, Hypera Postica (Coleoptera: Curculionidae)

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