Arthropod Scavengers of Colorado Potato Beetle (Leptinotarsa Decemlineata) Cadavers

The relative densities of ground-dwelling arthropod scavengers, and the disappearance rates of Beauveria bassiana-infected CPB cadavers, were investigated in three Maine potato fields during the summers of 2001 and 2002. Pitfall traps were used to assess scavenger relative abundance, and sentinel cadavers were placed in the fields and monitored for disappearance. For both years, cadaver disappearance rates were greatest in the fields that caught the most carabids. In 2002, cages of different mesh sizes were placed around sentinel cadavers to exclude predators according to size. There were no differences in rates of cadaver disappearance from artificial substrates that had no cages, large mesh (14 mm2) cages, and medium mesh (7 mm2) cages, but disappearance rates were lower from substrates with small mesh (4 mm2) cages. This suggests that the predominant scavenger is between 4 and 7 mm in diameter, which corresponds to the species of carabids captured during the study. Laboratory feeding trials were conducted in 2002 with carabids collected from the field to examine palatability of CPB cadavers of different qualities. In no-choice feeding trials, all carabid species tested consumed diseased cadavers within 24 hours. Pterostichus melanarius consumed more diseased cadavers than any of the other species. In preference feeding trials, all carabid species consumed diseased cadavers, and there was no difference between consumption rates of non-diseased and diseased cadavers. The longevity of some carabids was compared between one group that had never consumed diseased cadavers nor had ever been in contact with sporulated cadavers, and another group that had consumed diseased cadavers or had been in contact with sporulated cadavers. Mortality did not differ significantly between these groups suggesting that Beauveria bassiana has no adverse effect on carabid beetles scavenging on diseased Colorado potato beetle cadavers.