Canadian Forest Service Publications
Transmission of some insect viruses with particular reference to ovarial transmission and its importance in the development of epizootics. 1961. Bird, F.T. Journal of Insect Pathology 3:352-380.
Issued by: Great Lakes Forestry Centre
Catalog ID: 34317
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Three sawflies, Diprio1t hercy1tiae (Hartig), NeodipriOtz sertiJer (Geoffroy), and NeodipriOtz lecOtztei (Fitch) are su~ceptible to highly virulent polyhedrosis viruses. The viruses are transmitted via eggs of infected females and kill young progeny at an early stage of larval development. The bodies of these larvae are the source of infection of the progeny of healthy females and initiate epizootics. Severe epizootics may result from the infection of less than 10 per cent of the eggs. Once an epizootic is initiated, the viruses spread very rapidly. Rain appears to be the chief agent responsible for spreading virus throughout a tree whereas natural enemies of the sawflies, particularly insect parasites, appear to be the chief agents, besides the infected sawfly females, for transmitting virus from tree to tree. Epizootics increase in intensity and reach their peaks during the end of the season. The survival of one sex may be greater than another in those cases where one sex completes its development earlier in the season. A fourth sawfly, Neodiprio1t pratti ba1tksia,zae Rohwer, is susceptible to a mild type of polyhedrosis virus and although heavy mortality results when suspensions of the virus are sprayed on trees upon which larvae are feeding, no mortality or evidence of infection has been observed among the progeny of the insects that survive.