Section I: Biological Control (4 of 12)
 

Editorial note: The authors served as an independent review team and prepared this report on Nosema locustae in 1991 at the request of the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine’s Grasshopper Integrated Pest Management Project. The internal report contains guidelines and recommendations for the use of Nosema locustae and is reproduced in the User Handbook because of the importance of the information the report contains. The present version has been edited to be consistent in style and tone with the User Handbook.

I.4 Utility of Nosema locustae in the Suppression of Rangeland Grasshoppers

James L. Vaughn, Wayne M. Brooks, John L. Capinera, Terry L. Couch, and Joe V. Maddox

Nosema locustae is a microsporidium pathogenic (disease-causing) to a wide range of grasshoppers (more than 90 species are susceptible). It can be easily mass produced and formulated in baits for use as a biological control agent. Although many species of microsporidia are known to act as important naturally occurring biological control agents of insects, very few can be appropriately used as traditional microbial insecticides.

Laboratory studies, simulation models, and some field experiments suggest that N. locustae may be successfully utilized for long-range grasshopper control. But there is little or no evidence that N. locustae can be used effectively as a microbial insecticide for short-term control of grasshopper populations.

Inducing infections in insect populations is, at best, difficult. Many variables affect the onset and duration of an epizootic (disease outbreak). In the case of grasshoppers, the number and extent of variables are especially troublesome. The number of grasshopper species present, age of grasshoppers, and population density all influence the outcome of field applications. Therefore, the use of N. locustae as a grasshopper biological control agent should be considered as part of a long-term suppression effort but not as a microbial insecticide in direct competition with chemical pesticides.

Diseases that affect insects should have great potential for grasshopper control primarily because many grasshopper species readily eat bait into which pathogens can be incorporated. The extensive information generated by Nosema locustae studies will be of great help in this area. Domestic and international efforts should be made to identify and isolate other grasshopper pathogens for use as biological control agents.

In preparation for the analysis that is the foundation for this chapter, we were provided with a number of documents, including representative scientific publications, annual reports, and technical reports (see attached list). In addition, we discussed selected questions with Jerome Onsager, Robert Staten, and Jan Meneley.

After consideration of this information, we made the following specific recommendations:

1. Nosema locustae should be used to suppress rangeland grasshoppers in environmentally sensitive areas where cost, rapid knockdown, and high levels of control are not primary concerns. In such areas where insecticidal applications are not possible, continued use of N. locustae may be warranted. In these areas it may aid in the long-term management of the pest, and its use may allow researchers to address some of the important ecological questions surrounding it. These subjects are discussed in the following section.

2. Higher rates and/or multiple applications should be used where environmental sensitivities outweigh the higher costs involved.

In most of the past field tests with N. locustae, the dosage rate of 1 x 10⁹ spores per acre appears to have been predicated more on the economics involved in a grasshopper control program rather than on the actual dose required for effective grasshopper suppression. As estimates of the number of spores per bran flake at this standard rate of application are considerably below LD₅₀ (the dose where 50 percent of exposed individuals are killed) rates for Melanoplus sanguinipes and M. bivittatus, the effectiveness of higher dosage rates needs further evaluation. Laboratory bioassays support the enhanced effectiveness of Nosema locustae at higher dosages, although field studies have produced conflicting results.

In tests with up to five times the standard rate, greater reductions in grasshopper densities have not been obtained. However, in tests with 100 times the standard rate and where small field cages were also used to evaluate treatment effectiveness, grasshopper mortality was significantly higher, at least with M. sanguinipes. Despite the obvious costs of using higher dosage rates, the potential for enhancing the effectiveness of a readily available and registered biological control agent for use in environmentally sensitive areas may outweigh economic considerations.

In these sensitive areas where higher dosage rates and multiple applications of spores may be used, the methods of evaluation should be improved to include confinement of known numbers of the various grasshopper species in laboratory and field cages. Thus, along with monitoring population densities at appropriate time intervals in field plots, known numbers of treated and untreated grasshoppers should be confined in small field cages on untreated rangeland as well as under laboratory conditions. This evaluation plan will allow more accurate estimates of N. locustae’s primary effects on infection and mortality rates, as well the secondary effects on grasshopper food consumption, longevity, fecundity (reproductive capability), and vertical transmission.

3. Use of Nosema locustae at presently recommended dosages does not reliably provide an adequate level of suppression. N. locustae has been shown to induce measurable reductions in grasshopper longevity, fecundity, and consumption rates under controlled conditions in laboratory and field cages. Also, numerous examples from Canada and the United States indicate that it is possible to obtain significant reductions in grasshopper numbers and damage under field conditions using Nosema. However, results are not consistent. Reports of apparent failure also exist and many of the “testimonial-type” data are suspect. Reasons given for the apparent failure of Nosema locustae to suppress grasshoppers include

a. Suboptimal applications of the product: low-quality spores, bad weather, equipment failure, etc.

b. Poor targeting of the product: grasshopper species of low susceptibility or in the wrong development stage.

c. Incorrect assessment of the product: inadequate sampling or poor experimental design.

d. Unreasonable expectations of the product: applicators, evaluators, and land managers expect insecticidal activity from a product that inherently cannot provide rapid or high levels of control.

As long as there are available insecticides that do provide high levels of control (70–95 percent is normal), control by N. locustae (30–40 percent under the best of conditions) will appear inadequate to ranchers and others concerned with economical, reliable grasshopper suppression. Until the basis for the inconsistencies is better understood, N. locustae should be reserved for areas where high levels of control are not essential, or where chemical insecticide usage is not a viable option.

If N. locustae is used in ecologically sensitive areas, then research should be conducted to determine the stability characteristics of the formulated bran product. Although data in the literature support the conclusion that the N. locustae inoculum is active at the time of formulation, nothing in the literature describes the viability of the N. locustae formulations just prior to aerial application.

Pathogens that affect insects are markedly sensitive to elevated temperatures, and significant reduction of activity occurs at temperatures as low as 104 °F (40 °C). If no special handling of the N. locustae formulation is routinely done as part of the application program, it is conceivable that the bran formulation could be exposed to temperatures during transit and site storage which could cause a significant, serious biological degradation of the product. It is possible that, in several of the studies, site storage conditions could have had a severe negative effect on the formulation.

Therefore, the committee suggests that a thermal death time-study be developed for the N. locustae formulation and storage parameters be defined for the product. These steps will ensure that, if and when future applications are made, shipping specifications and site storage requirements of the formulations can be adjusted to preserve the material’s efficacy. With handling protocols in place, the viability of the product can be assured up to the point of application.

In addition, bioassays of samples of the N. locustae bran formulation from the aircraft hopper should accompany each application. Information from these assays will aid in determining if the formulation was shipped and stored under the proper conditions as specified by data obtained from the thermal death time-study.

Additional research on application techniques other than bait seem warranted given the dearth of information in the literature. In particular, conventional low-volume and ultralow-volume liquid applications, with various adjuvants (additives) to increase droplet deposition and decrease evaporation, should be investigated.

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Nosema locustae References

Availability note: Several of the following citations come from annual reports prepared for the Grasshopper Integrated Pest Management Project but not distributed outside the Animal and Plant Health Inspection Service. Individual photocopies of these materials are available on request from USDA, APHIS, Plant Protection and Quarantine, 4700 River Road, Riverdale, MD 20737. 

Brooks, W. M. 1988. Entomogenons protozoa. In: Ignoffo, C. M. ed. CRC handbook of natural pesticides, vol. 5: Microbial insecticides, part A. Boca Raton, FL: CRC Press: 1–149.

Erlandson, M. A.; Ewen, M. K.; Mukerji, M. K.; Gillott, C. 1986. Susceptibility of immature stages of Melanoplus sanguinipes to Nosema cuneatum Henry and its effect on host fecundity. Canadian Entomologist 118: 29–35.

Ewen, A. B.; Mukerji, M. K. 1980. Evaluation of Nosema locustae (Microsporida) as a control agent of grasshopper populations in Saskatchewan. Journal of Invertebrate Pathology 35: 295–303.

Germida, J. J.; Ewen, A. B.; Onofriechuk, E. E. 1987. Nosema locustae Canning (Microsporida) spore populations in treated field soils and resident grasshopper populations. Canadian Entomologist 119: 355–360.

Henry, J. E. 1969. Extension of the host range of Nosema locustae in Orthoptera. Annals of Entomological Society of America 62: 452–453.

Henry, J. E. 1971. Experimental application of Nosema locustae for control of grasshoppers. Journal of Invertebrate Pathology 18: 389–394.

Henry, J. E. 1971. Nosema cuneatum sp.n. (Microsporida: Nosematidae) in grasshoppers (Orthoptera: Acrididae). Journal of Invertebrate Pathology 17: 164–171.

Henry, J. E. 1972. Epizootiology of infections by Nosema locustae Canning (Microsporida: Nosematidae) in grasshoppers. Acrida 1: 111–120.

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Henry, J. E. 1981. The value of Nosema locustae in control of grasshoppers. U.S. Agency for International Development regional food crop protection project: Biological control of pests. Unpublished paper in Dakar, Senegal. Feb. 9–13.

Henry, J. E. 1982. Production and commercialization of microbials— Nosema locustae and other protozoa. In: Invertebrate pathology and microbial control proceedings, IIIrd international colloquium on invertebrate pathology; 6–10 September 1982; Brighton, UK. [Place of publication unknown]: Society of Invertebrate Pathology: 103–106.

Henry, J. E. 1985. Effect of grasshopper species, cage density, light intensity, and method of inoculation on mass production of Nosema locustae (Microsporida: Nosematidae). Journal of Economic Entomology 78: 1245–1250.

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Henry, J. E.; Oma, E. A. 1974. Effect of prolonged storage of spores on field applications of Nosema locustae (Microsporida: Nosematidae) against grasshoppers. Journal of Invertebrate Pathology 23: 371–377.

Henry, J. E.; Onsager, J. A. 1982. Large-scale test of control of grasshoppers on rangeland with Nosema locustae. Journal of Economic Entomology 75: 31–35.

Henry, J. E.; Onsager, J. A. 1982. Experimental control of the Mormon cricket, Anabrus simplex, by Nosema locustae (Microsporida: Nosematidae), a protozoan parasite of grasshoppers (Orthoptera: Acrididae). Entomophaga 27: 197–201.

Henry, J. E.; Oma, E. A.; Onsager, J. A. 1978. Infection of the corn earworm, Heliothis zea, with Nosema acridophagus and Nosema cuneatum from grasshoppers: relative virulence and production of spores. Journal of Invertebrate Pathology 34: 125–132.

Henry, J. E.; Oma, E. A.; Onsager, J. A. 1978. Relative effectiveness of ULV spray applications of spores of Nosema locustae against grasshoppers. Journal of Economic Entomology 71: 629–632.

I. 4–3.Henry, J. E.; Tiahrt, K.; Oma, E. A. 1973. Importance of timing, spore concentrations, and levels of spore carrier in applications of Nosema locustae (Microsporida: Nosematidae) for control of grasshoppers. Journal of Invertebrate Pathology 21: 263–272.

Hildreth, M. B.; Fuller, B. 1990. Laboratory bioassay to compare virulence of grasshopper pathogens such as Nosema locustae from different sources. In: Cooperative Grasshopper Integrated Pest Management Project, 1990 annual report. Boise, ID: U.S. Department of Agriculture, Animal and Plant Health Inspection Service: 204–209.

Hildreth, M. D.; Walgenbach, D. D. 1990. Pathological effects of increased concentrations of Nosema locustae on two different grasshopper species with different susceptibilities. In: Cooperative Grasshopper Integrated Pest Management Project, 1990 annual report. Boise, ID: U.S. Department of Agriculture, Animal and Plant Health Inspection Service: 196–201.

Hirsch, D. N.; Foster, N.; Smith, M.; Battaglia, T.; Morgans, M. 1988. Two year evaluation of the 1987 Nosema locustae grasshopper control block, North Dakota. In: Cooperative Grasshopper Integrated Pest Management Project, 1988 annual report. Boise, ID: U.S. Department of Agriculture, Animal and Plant Health Inspection Service: 47–51.

Jech, L.; Foster, N.; Sluss, T.; Keim, D.; Miller, J.; Franklin, G. 1990. Application of Nosema locustae treated bran bait on grasshopper populations near Delta Junction, Alaska. In: Cooperative Grasshopper Integrated Pest Management Project, 1990 annual report. Boise, ID: U.S. Department of Agriculture, Animal and Plant Health Inspection Service: 55–57.

Johnson, D. L. 1987. Evaluation of grasshopper control with Nosema locustae and insecticide on bran carrier. In: Farming for the future. Final Rep. 84-0418. Lethbridge, CN: Agriculture Canada. [Unpublished.] 41 p.

Johnson, D. L.; Henry, J. E. 1987. Low rates of insecticides and Nosema locustae (Microsporida: Nosematidae) on baits applied to roadside for grasshopper (Orthoptera: Acrididae) control. Journal of Economic Entomology 80: 685–689.

Johnson, D. L.; Pavlikova, E. 1986. Reduction of consumption by grasshoppers (Orthoptera: Acrididae) infected with Nosema locustae (Microsporida: Nosematidae). Journal of Invertebrate Pathology 48: 232–238.

Lockwood, J. A. 1988. Biology and recommendations for use of Nosema locustae Canning: a biological control agent of grasshoppers. Bull. B-917. Laramie, WY: University of Wyoming and Wyoming Agricultural Experiment Station.

Lockwood, J. A. 1989. Cannibalism in rangeland grasshoppers (Orthoptera: Acrididae) attraction to cadavers. Journal of the Kansas Entomological Society 61: 379–387.

Lockwood, J. A; DeBrey, L. D. 1990. Direct and indirect effects of Nosema locustae (Canning) (Microsporida: Nosematidae) on rangeland grasshoppers (Orthoptera: Acrididae). Journal of Economic Entomology 83: 377–383.

Lockwood, J. A.; Larsen, J. C. 1988. Nosema locustae: principles, promises and problems. In: Proceedings, 44th Wyoming weed and pest conference; [date of meeting unknown; Douglas, WY. [Place of publication and publisher unknown]: 18–25.

MacVean, C. M.; Capinera, J. L. 1991. Pathogenicity and transmission potential of Nosema locustae and Vairimorpha n.sp. (Protozoa: Microsporida) in Mormon crickets (Anabrus simplex: Orthoptera: Tettigoniidae). Journal of Invertebrate Pathology 57: 23–36.

Morris, O. N. 1985. Susceptibility of the migratory grasshopper, Melanoplus sanguinipes (Orthoptera: Acrididae), to mixtures of Nosema locustae (Microsporida: Nosematidae) and chemical insecticides. Canadian Entomologist 117: 131–132.

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