Application of viral insecticides

Methodologies most often used for formulation and application of viral insecticides are those developed for conventional chemical insecticides. Viral insecticides are most effectively formulated as wettable powders by lyophilization or spray dry methods. These formulations are best standardized using both counts of occluded virus particle concentration and bioassay activity. Viral insecticides are typically applied as sprays against larval pests of Lepidoptera and Hymenoptera (sawfly) using both aerial and ground equipment. Spray parameters for viral insecticides are not well understood and available equipment is not suitable for their most efficaceous use. Much of the research on virus application has been on development of adjuvants for tank mixtures to overcome problems with plant coverage and sunlight inactivation. 

The numerous research programs around the world on development of viral insecticides have resulted in a wide array of technical reports on their formulation and application. There is little current research in this area, and available information has been reviewed in depth in numerous reviews (4, 8-14). This report will summarize progress in these areas and elaborate on areas where the need for additional progress is most critical. 

Viral insecticides kill slowly and result in lower mortalities than chemical insecticides in most instances. This often dictates that virus application be directed against pest populations of lower density than would be necessary for chemical insecticides. The lower levels of control obtained and the short residual period of viral insecticides may also require that virus treatments be timed closer together and applied more often than for chemical insecticides. Because viral insecticides are less effective than chemicals in producing quick results, they are less likely to control high population densities of the target population. Because producers are accustomed to evaluating the effectiveness of the fast-acting chemical insecticides, they find it difficult to delay their evaluation of virus application for the several days or even weeks often required for treated larvae to die (31). If not properly trained, users may switch to chemical insecticides prematurely and never realize that the virus would have been efficaceous. 

Production practices and availability of equipment require that viral insecticides be formulated and applied using technology designed for application of contact insecticides. Development of formulation and application methodology for viral insecticides has not proceeded as rapidly as anticipated. Many viral insecticides are efficaceous, but research has slowed because few are marketed. Although viral insecticide use is limited, their potential for use in IPM systems where other pesticides are not available or desirable provides a window of opportunity for greater use in the future. Improvements in formulation and application technology... 

When a viral insecticide is applied against a subeconomic population for control of succeeding generations, it may be desirable to direct the application to larger larvae. The quantity of polyhe-... 

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