Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: May 17, 2004
Publication Date: August 1, 2004
Citation: Wraight, S.P., Ramos, M. 2004. Investigations of colorado potato beetle mortality following foliar applications of beauveria bassiana [abstract]. Society for Invertebrate Pathology Annual Meeting Proceedings. 37:103. Technical Abstract: The fungus Beauveria bassiana (Bb) has the potential to kill Colorado potato beetle larvae within a few days after infection. However, under suboptimal conditions, (e.g., during hot weather), pathogenesis is slowed, allowing the beetles to complete larval development and enter the soil to pupate. Little is known about the fate of these larvae. A field population of beetle larvae was exposed to sprays of Bb strain GHA (each at 2.5 x 1013 conidia/ha). Treatments included a series of 4 sprays at 3-4 day intervals targeting early instars (4X treatments), a single spray targeting large larvae (1X treatments), and a carrier control. Larval populations were sampled until development was completed; mature larvae were collected immediately as they dropped to the ground and placed in soil cages (20 larvae/cage). Results revealed 1) 22% mortality among larvae taken from controls and placed in soil cages in control plots; 2) 16-17% mortality among larvae taken from control plots and placed in soil in 1X or 4X treatment plots; 3) 37-38% mortality among larvae taken from either the 1X or 4X plots and placed in control soil; 4) 50% mortality among larvae taken from 1X plots and placed in 1X-treated soil; and 5) 51% mortality among larvae taken from 4X plots and placed in 4X soil. Counts of larvae prior to drop indicated 0% and 31% reductions in larval numbers relative to controls in the 1X and 4X plots respectively. Counts of emerged adults feeding in the plots ultimately indicated 50% and 70% reductions in numbers of 1X and 4X treated beetles, respectively. These results showed that mortality in the soil was due primarily to infections acquired from the foliar sprays and that sprays against large larvae were more efficient than sprays against small larvae.