Use of insect pathogen Bacillus thuringiensis for control of grubs (Coleoptera: Scarabaeidae) in turf
Leslie C. Lewis
The objectives of this dissertation were to broaden and more greatly define the host range of Bacillus thuringiensis ( Bt) subspecies against U.S. turfgrass grub pests, investigate a novel technique for use of Bt, specifically its use in turf to control white grubs (Coleoptera: Scarabaeidae) and evaluate parameters for the successful safe and effective application of Bt in turfgrass for control of white grubs;An evaluation was performed for host range of Bt tolworthi, kumamotoensis , and japonensis against the following scarab turfgrass pests Anomala cuprea, Atenius sp., Cotinis sp., Cyclocephala borealis, Cyclocephala lurida, Cyclocephala pasadenae, Popillia japonica, Phyllophaga sp. Results showed Bt s tolworthi and Bt japonensis to have activity against U.S. economic grub pests Cyclocephala borealis, Cyclocephala lurida, and Popillia japonica while Bt kumamotoensis was active against Cotinis sp. Other pests tested, Atenius sp. and Phyllophaga sp. had no detectable susceptibility to any of the three isolates;Leptinotarsa rubiginosa (Coleoptera: Chrysomelidae) which is susceptible to Bt tolworthi was used to indicate placement of the bacterium after application to turf. The bioassay indicated that Bt tolworthi was recovered the same day from both sites up to depths of 2 cm after a suspension of 800 ug/ml was applied at rates of 1,870 and 9,350 l/ha (200 and 1,000 gallons per acre) followed by 0.75 cm irrigation;A sampling regime of rifamycin-resistant Bt japonensis was used to study placement of this bacterium in U.S. Golf Association creeping bentgrass green at Iowa State University Horticulture Station. Thirty ml of the Bt suspension containing ∼5.7 x 1011 colony forming units was sprayed in an application volume equivalent of 467, 935 and 1870 l/ha proceeded by 0, 1 or 2 cm of irrigation equivalent to 1.2 x 0.9-m turf plots. Turf soil was sampled to a depth of 11 cm on Days 0, 1, 6 and 60. Higher volumes of irrigation resulted in greater recovery of colony-forming units beneath the grass and thatch layer. This study offers insight that the use of Bt bioinsecticide application to turf fits with conventional turfgrass management.