Temporal patterns of mortality from an entomopoxvirus and strategies for control of the migratory grasshopper (Melanoplus sanguinipes F.)
1992
Woods, S.A. | Streett, D.A. | Henry, J.E.
The temporal pattern of mortality was investigated in a laboratory population of the migratory grasshopper, Melanoplus sanguinipes (F.), following per os inoculation with the M. sanguinipes entomopoxvirus. The effects of starvation and dosage on the temporal pattern and the implications for the epizootiology of this virus were also investigated. The temporal pattern of mortality was characterized by two modes. The first mode of mortality occurred prior to ca. 12 days postinoculation (PI), and 98.9% of the cadavers were devoid of spheroids (the occluded form of the virus). The second mode of mortality began after ca. 14 days PI. Spheroids were present in 92% of the grasshoppers that died on or after Day 16. The timing of spheroid formation corresponded with the time after which cadaver homogenates were infectious, which suggested that the occluded form of the virus is necessary for transmission in the field. Percent infection and rates of early mortality increased with dosage; however, the number of infected grasshoppers that survived long enough to produce spheroids was negatively related to dosage. Our observations suggest that high application rates may be desirable in field control efforts where a rapid reduction in host density is necessary. Alternatively, reduced rates might be of more value at lower grasshopper densities, when transmission between grasshoppers in the field is desired to retard population growth.
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