Bait formulations to deliver entomopathogenic fungi to grasshoppers and Mormon crickets

The typical application tactic for using fungi to control grasshoppers and locusts is a broadcast, ULV application of fungus conidia in an oil carrier. Baits, commonly used to deliver carbaryl or Paranosema locustae to grasshopper populations, offer an alternative approach. A bait can concentrate a dose of fungus and avoid necessity of direct spray onto grasshoppers, making delivery more efficient, potentially decreasing efficacious rate of conidia per unit area. Metarhizium robertsii DWR2009 conidia were formulated on wheat bran at a titer of 1.1x10¹³ conidia Kg^-1, with canola oil binder at 7.5% v/w and applied at 5, 10, 20 or 40 Kg ha^-1 to typical Northern Plains prairie (carbaryl baits are typically applied at 5-10 Kg ha^-1 in the U.S.) There were 5 (A. simplex) or 6 (M. sanguinipes) independent replicate tests. To avoid the strong deleterious effect of behavioral fever on fungus infection, so that we could demonstrate the validity of this approach, adult Melanoplus sanguinipes or Anabrus simplex were caged on treated prairie ground for 3 days then incubated 14 days in the laboratory. Efficacy among M. sanguinipes ranged from 57-96% and on A. simplex 92-100%, depending on rate, with high prevalence of mycosis. With a fungus that better tolerates behavioral fever, such as Metarhizium acridum, which has been successful against Acrididae in Africa and Asia, such baits might offer an advantage over broadcast sprays.