Key parameters of alfalfa weevil larval mortality by Entornophthora phytonorni were compared weekly in three alfalfa fields. Rainfall appeared to be the overriding factor in seasonal larval infection rates

Armbrust, Edward J

Barney, Robert J

English

ValpoScholar

The Great Lakes Entomologist 
Volume 14 
Number 1 - Spring 1981 Number 1 - Spring 1981 Article 10 
April 1981 
Key Parameter Comparisons of Fungal Induced Mortality in 
Alfalfa Weevil Larvae (Coleoptera: Curculionidae) 
Robert J. Barney 
Illinois Natural History Survey and Illinois Agricultural Experiment Station 
Edward J. Armbrust 
Illinois Natural History Survey and Illinois Agricultural Experiment Station 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Barney, Robert J. and Armbrust, Edward J. 1981. "Key Parameter Comparisons of Fungal Induced 
Mortality in Alfalfa Weevil Larvae (Coleoptera: Curculionidae)," The Great Lakes Entomologist, vol 14 (1) 
Available at: https://scholar.valpo.edu/tgle/vol14/iss1/10 
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. 
THE GREAT LAKES ENTOMOLOGIST 
KEY PARAMETER COMPARISONS OF FUNGAL INDUCED 
MORTALITY IN ALFALFA WEEVIL LARVAE (COLEOPTERA: 
CURCULIONIDAE) 
Robert J. Barney and Edward J. ~ rmbrus t2  
ABSTRACT 
Key parameters of alfalfa weevil larval mortality by Entornophthora phytonorni were com- 
pared weekly in three alfalfa fields. Rainfall appeared to be the overriding factor in seasonal 
larval infection rates. 
The fungus, Entornophthora (= Zoophthora) phytonorni (Zygomycetes: Entomophtora- 
ceae), was first detected in larvae of the alfalfa weevil, Hypera postica Gyllenhal (Coleop- 
tera: Curculionidae), in Illinois in 1979 (Barney et al. 1980). Harcourt et al. (1974) and Puttler 
et  al. (1980) reported alfalfa weevil infection rates of over 90% in some alfalfa fields in 
Ontario and Missouri, respectively, and suggested that this fungus may become a key 
mortality factor. 
The objective of this paper is to compare the following key parameters of alfalfa weevil 
larval mortality by the fungus in three fields: H. postica host density, density of the clover 
leaf weevil, Hypera punctata (Fabricius), which is also infected by this fungus, and the 
infection rate in H. punctata larvae. 
MATERIALS AND METHODS 
Sampling was conducted in three alfalfa fields in Washington County, southern Illinois. 
On each sampling date, ten 0.09 m2 areas of alfalfa (1.0 ft2) from each field were removed to 
be placed on Berlese funnels in the laboratory (Barney et al. 1978). As the samples were 
being placed on the funnels, large (3rd and 4th instars) alfalfa weevil and clover leaf weevil 
larvae were picked out to be reared individually in plastic diet cups to determine the inci- 
dence of infection and parasitism. The larvae were reared individually to prevent the spread 
of infection to larvae which were not infected when removed from the field. The Berlese 
funnel measurements gave host densities by instar for both the alfalfa weevil and clover leaf 
weevil during the entire sampling period until cutting (2 April-7 May). 
RESULTS AND DISCUSSION 
Dead clover leaf weevil larvae were visually found on the alfalfa leaflets from 9 April to 23 
April. The mean number of infected larvae for the three fields increased from 6.1% on 9 
April to  25.096 on 7 May (3rd and 4th instars). 
The initial sighting of diseased alfalfa weevil larvae was 30 April. The mean number of 
infected larvae increased from 6.0% on 23 April to 21.6% on 7 May. A slightly greater 
percentage of 4th instars (25.5%) than 3rd instars (22.8%) were found to be diseased. 
l ~ h i s  research has been financed in part with Federal funds from the Environmental Protection Agency 
under grant number L 800 146, and in pan by the Illinois Agricultural Experiment Station and the Illinois 
Natural History Survey. The contents do not necessarily reflect the views and policies of the Environ- 
mental Protection Agency nor does mention of trade or commercial products constitute endorsement or 
recommendation for use. 
2~llinois Natural History Survey and Illinois Agricultural Experiment Station, Urbana, IL 61801. 
1
Barney and Armbrust: Key Parameter Comparisons of Fungal Induced Mortality in Alfalfa
Published by ValpoScholar, 1981
58 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No. I 
Table 1. Comparison of key parameters affecting alfalfa weevil mortality by Entomophthora 
phyronomi in three alfalfa fields in Washington County. Illinois, 1980. 
Alfalfa Fields 
Davis Shubert Karg 
H .  posrica % disease@ 45.6 17.3 4.9 
H .  postica densityab 200.1 84.3 164.3 
H .  puncfaru 9% diseaseda 13.9 17.6 2.4 
H .  punctata densityab 7.2 3.6 6.3 
aAverage over duration of sampling period. 
bper foot?. 
Harcourt et al. (1974) suggested that the key parameters in alfalfa weevil larval mortality 
by the fungus appear to be host density, temperature, rainfall, and the density of H .  punc- 
fafa which may serve as a reservoir for the fungus. A comparison of these parameters for the 
three study fields showed that the Davis field, which had the highest percentage of diseased 
alfalfa weevil larvae, had the greatest H .  posrica and H .  punctata densities (Table I.). 
However, the Karg field also had very high H .  postica and H .  punctata densities but had a 
very low incidence of larval infection for both species. 
The overriding factor in the incidence of E .  phyfonomi in alfalfa weevil larvae may be 
rainfall, and the resulting higher humidity. Watson et al. (in press) determined that high 
humidity was the primary factor initiating sporulation of E. phytonomi in alfalfa weevil 
larvae. The condition of high humidity protects against rapid dessication and inactivation of 
the conidea and is advantageous to further infections (Newman and Carner 1974). 
During last year's statewide survey for this fungus in alfalfa weevil larvae, we found many 
fields in this area to have infection rates greater than 80%. A comparison of rainfall data for 
this area in 1979 and 1980 showed a 78.9% decrease of April rainfall from 1979 to 1980. April 
1979 was an exceptionally wet month, 2.76 inches above normal, which may explain why the 
fungal incidence was so much greater in 1979 than 1980 in this area. 
In summary, there were some indications during this study that high host densities of both 
Hypera species and a high percentage of diseased H .  punctata larvae would facilitate the 
increase and spread of E. phyronomi through the H .  postica population. However, it appears 
that April 1980 was a period of very low precipitation which inhibited the conidial sporula- 
tion and spread of the fungus in both the H .  posrica and H .  punctata populations. 
LITERATURE CITED 
Barney, R. J., E. J. Armbrust, D. P. Bartell, and M. A. Goodrich. 1978. Frequency occur- 
rence of Bafhyplectes curculionis within instars of Hypera postica larvae in Illinois. 
Environ. Entomol. 7:241-245. 
Barney, R. J., P. L. Watson, K. Black, J. V. Maddox, and E. J. Armbrust. 1980. Illinois 
distribution of the fungus Ento~nophrhora phytonomi (Zygomycetes: Entomophthora- 
ceae) in larvae of the alfalfa weevil (Coleoptera: Curculionidae). Great Lakes Entomol. 
13: 149-150. 
Harcourt, D. G., J. C. Guppy, D. M. MacLeod, and D. Tyrrell. 1974. The fungus Ento- 
mophfhora phyronomi pathogenic to the alfalfa weevil, Hypera postica. Canadian Ento- 
mol. 106: 1295- 1300. 
Newman, G. G., and G. R. Carner. 1974. Die1 periodicity of Entomophrhora gammae in the 
soybean looper. Environ. Entomol. 3:888-890. 
Puttler, B., D. L. Hostetter, S. H. Long, and A. A. Borski. 1980. Seasonal incidence of the 
fungus Entomophrhora phytonolni infecting Hypera postica larvae in Central Missouri. J. 
Invert. Pathol. 35:99-100. 
Watson, P. L., R. J. Barney, J. V. Maddox, and E. J. Armbmst. Sporulation and mode of 
infection of Enromophrhora phyronomi, a pathogen of the alfalfa weevil. Environ. En- 
tomol. (in press) 
2
The Great Lakes Entomologist, Vol. 14, No. 1 [1981], Art. 10
https://scholar.valpo.edu/tgle/vol14/iss1/10


Key Parameter Comparisons of Fungal Induced Mortality in Alfalfa Weevil Larvae (Coleoptera: Curculionidae)

Robert J Barney

Edward J Armbrust

Crossref

Valparaiso University

The Great Lakes Entomologist Volume 14 Number 1 - Spring 1981 Number 1 - Spring 1981 Article 10 April 1981 Key Parameter Comparisons of Fungal Induced Mortality in Alfalfa Weevil Larvae (Coleoptera: Curculionidae) Robert J. Barney Illinois Natural History Survey and Illinois Agricultural Experiment Station Edward J. Armbrust Illinois Natural History Survey and Illinois Agricultural Experiment Station Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Barney, Robert J. and Armbrust, Edward J. 1981. "Key Parameter Comparisons of Fungal Induced Mortality in Alfalfa Weevil Larvae (Coleoptera: Curculionidae)," The Great Lakes Entomologist, vol 14 (1) Available at: https://scholar.valpo.edu/tgle/vol14/iss1/10 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. THE GREAT LAKES ENTOMOLOGIST KEY PARAMETER COMPARISONS OF FUNGAL INDUCED MORTALITY IN ALFALFA WEEVIL LARVAE (COLEOPTERA: CURCULIONIDAE) Robert J. Barney and Edward J. ~ rmbrus t2  ABSTRACT Key parameters of alfalfa weevil larval mortality by Entornophthora phytonorni were com- pared weekly in three alfalfa fields. Rainfall appeared to be the overriding factor in seasonal larval infection rates. The fungus, Entornophthora (= Zoophthora) phytonorni (Zygomycetes: Entomophtora- ceae), was first detected in larvae of the alfalfa weevil, Hypera postica Gyllenhal (Coleop- tera: Curculionidae), in Illinois in 1979 (Barney et al. 1980). Harcourt et al. (1974) and Puttler et  al. (1980) reported alfalfa weevil infection rates of over 90% in some alfalfa fields in Ontario and Missouri, respectively, and suggested that this fungus may become a key mortality factor. The objective of this paper is to compare the following key parameters of alfalfa weevil larval mortality by the fungus in three fields: H. postica host density, density of the clover leaf weevil, Hypera punctata (Fabricius), which is also infected by this fungus, and the infection rate in H. punctata larvae. MATERIALS AND METHODS Sampling was conducted in three alfalfa fields in Washington County, southern Illinois. On each sampling date, ten 0.09 m2 areas of alfalfa (1.0 ft2) from each field were removed to be placed on Berlese funnels in the laboratory (Barney et al. 1978). As the samples were being placed on the funnels, large (3rd and 4th instars) alfalfa weevil and clover leaf weevil larvae were picked out to be reared individually in plastic diet cups to determine the inci- dence of infection and parasitism. The larvae were reared individually to prevent the spread of infection to larvae which were not infected when removed from the field. The Berlese funnel measurements gave host densities by instar for both the alfalfa weevil and clover leaf weevil during the entire sampling period until cutting (2 April-7 May). RESULTS AND DISCUSSION Dead clover leaf weevil larvae were visually found on the alfalfa leaflets from 9 April to 23 April. The mean number of infected larvae for the three fields increased from 6.1% on 9 April to  25.096 on 7 May (3rd and 4th instars). The initial sighting of diseased alfalfa weevil larvae was 30 April. The mean number of infected larvae increased from 6.0% on 23 April to 21.6% on 7 May. A slightly greater percentage of 4th instars (25.5%) than 3rd instars (22.8%) were found to be diseased. l ~ h i s  research has been financed in part with Federal funds from the Environmental Protection Agency under grant number L 800 146, and in pan by the Illinois Agricultural Experiment Station and the Illinois Natural History Survey. The contents do not necessarily reflect the views and policies of the Environ- mental Protection Agency nor does mention of trade or commercial products constitute endorsement or recommendation for use. 2~llinois Natural History Survey and Illinois Agricultural Experiment Station, Urbana, IL 61801. 1Barney and Armbrust: Key Parameter Comparisons of Fungal Induced Mortality in AlfalfaPublished by ValpoScholar, 198158 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No. I Table 1. Comparison of key parameters affecting alfalfa weevil mortality by Entomophthora phyronomi in three alfalfa fields in Washington County. Illinois, 1980. Alfalfa Fields Davis Shubert Karg H .  posrica % disease@ 45.6 17.3 4.9 H .  postica densityab 200.1 84.3 164.3 H .  puncfaru 9% diseaseda 13.9 17.6 2.4 H .  punctata densityab 7.2 3.6 6.3 aAverage over duration of sampling period. bper foot?. Harcourt et al. (1974) suggested that the key parameters in alfalfa weevil larval mortality by the fungus appear to be host density, temperature, rainfall, and the density of H .  punc- fafa which may serve as a reservoir for the fungus. A comparison of these parameters for the three study fields showed that the Davis field, which had the highest percentage of diseased alfalfa weevil larvae, had the greatest H .  posrica and H .  punctata densities (Table I.). However, the Karg field also had very high H .  postica and H .  punctata densities but had a very low incidence of larval infection for both species. The overriding factor in the incidence of E .  phyfonomi in alfalfa weevil larvae may be rainfall, and the resulting higher humidity. Watson et al. (in press) determined that high humidity was the primary factor initiating sporulation of E. phytonomi in alfalfa weevil larvae. The condition of high humidity protects against rapid dessication and inactivation of the conidea and is advantageous to further infections (Newman and Carner 1974). During last year's statewide survey for this fungus in alfalfa weevil larvae, we found many fields in this area to have infection rates greater than 80%. A comparison of rainfall data for this area in 1979 and 1980 showed a 78.9% decrease of April rainfall from 1979 to 1980. April 1979 was an exceptionally wet month, 2.76 inches above normal, which may explain why the fungal incidence was so much greater in 1979 than 1980 in this area. In summary, there were some indications during this study that high host densities of both Hypera species and a high percentage of diseased H .  punctata larvae would facilitate the increase and spread of E. phyronomi through the H .  postica population. However, it appears that April 1980 was a period of very low precipitation which inhibited the conidial sporula- tion and spread of the fungus in both the H .  posrica and H .  punctata populations. LITERATURE CITED Barney, R. J., E. J. Armbrust, D. P. Bartell, and M. A. Goodrich. 1978. Frequency occur- rence of Bafhyplectes curculionis within instars of Hypera postica larvae in Illinois. Environ. Entomol. 7:241-245. Barney, R. J., P. L. Watson, K. Black, J. V. Maddox, and E. J. Armbrust. 1980. Illinois distribution of the fungus Ento~nophrhora phytonomi (Zygomycetes: Entomophthora- ceae) in larvae of the alfalfa weevil (Coleoptera: Curculionidae). Great Lakes Entomol. 13: 149-150. Harcourt, D. G., J. C. Guppy, D. M. MacLeod, and D. Tyrrell. 1974. The fungus Ento- mophfhora phyronomi pathogenic to the alfalfa weevil, Hypera postica. Canadian Ento- mol. 106: 1295- 1300. Newman, G. G., and G. R. Carner. 1974. Die1 periodicity of Entomophrhora gammae in the soybean looper. Environ. Entomol. 3:888-890. Puttler, B., D. L. Hostetter, S. H. Long, and A. A. Borski. 1980. Seasonal incidence of the fungus Entomophrhora phytonolni infecting Hypera postica larvae in Central Missouri. J. Invert. Pathol. 35:99-100. Watson, P. L., R. J. Barney, J. V. Maddox, and E. J. Armbmst. Sporulation and mode of infection of Enromophrhora phyronomi, a pathogen of the alfalfa weevil. Environ. En- tomol. (in press) 2The Great Lakes Entomologist, Vol. 14, No. 1 [1981], Art. 10https://scholar.valpo.edu/tgle/vol14/iss1/10

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Key Parameter Comparisons of Fungal Induced Mortality in Alfalfa Weevil Larvae (Coleoptera: Curculionidae)

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