Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2012
Publication Date: 12/20/2012
Citation: Unruh, T.R., Lacey, L.A., Headrick, H.L., Pfannenstiel, R.S. 2012. The effect of the granulosis virus (PapyGV) on larval mortality and feeding behavior of the Pandemis leafroller Pandemis pyrusana (Kearfott)(Lepidoptera: Tortricidae). Biocontrol Science and Technology. 22:981-990. Interpretive Summary: Leafroller moths are significant pests in pear, peach, and cherry orchards in western states. Control of leafrollers usually requires broad-spectrum insecticides in spring and again in midsummer and these sprays can upset biocontrol in orchards. Researchers at Washington State University, Wenatchee and the USDA-ARS laboratory in Wapato WA described an insect virus discovered in Washington orchards, which specifically attacks the Pandemis leafroller. ARS scientists in Wapato evaluated how the concentration of virus affects feeding activity and time to kill of the leafroller to determine how to reduce pest populations and their feeding damage. The virus nearly always killed the leafroller and reduced leafroller larvae feeding damage by 75% following applications of economically practical virus concentrations. Like other insect viruses, the Pandemis granulosis virus was deactivated by solar radiation. In summary, the Pandemis granulovirus has potential for commercial development for population and damage suppression of the Pandemis leafroller but additional research to discover a solar protectant is highly desirable.
Technical Abstract: A granulosis virus (PapyGV) of the Pandemis leafroller, Pandemis pyrusana (Kearfott, discovered in Washington State, was studied in the laboratory and greenhouse to determine how the virus affected mortality rates of the leafrollers. Mortality rate was a function of both larval age and virus concentration. Moderately low concentrations of virus (20 and 200 virus occlusion bodies (OBs)/mm2) resulted in mortality of 60-95% in neonate leafrollers after 14 days of exposure. Higher concentrations of virus (2000-10000) resulted ranging from 85 to 100% after only 7 days. After exposure to 20-2000 OBs/mm2 treated diet, fourth instar P. pyrusana consumed 20-80% less area of apple leaves compared to control larvae. All fourth instars exposed to these doses succumbed before eclosion but time to death was prolonged. In a greenhouse study, all neonates, which fed on apple seedlings that had been sprayed to drip with 3 x 106 OBs/ml, failed to complete development and had a higher mortality rate than untreated larvae. Exposure of virus to 765 Watts/m2 for one hour in a solar simulator caused complete loss of virus activity. This virus shows promise for population regulation and can produce reduction in feeding damage.