BIOLOGICAL CONTROLÐMICROBIALS Beauveria bassiana Horizontal Infection Between Cadavers and Adults of the Colorado Potato Beetle, Leptinotarsa decemlineata (Say)

The behavior of adult Colorado potato beetles (Leptinotarsa decemlineata) in the presence of Beauveria bassiana sporulating on cadavers was studied to determine the likelihood of disease infection as beetles emerge from the soil and colonize host plants. In 2001, the movement of single adultColoradopotatobeetleswasmonitored in arenas containing infective cadavers in differing spatial patterns between four potato plants. In 2002, a similar designwas used, but was under themore natural conditions of a potatoÞeld. Inboth experiments, direction, time, anddirectness of beetle travel was not signiÞcantly affected by the presence or absence of infective cadavers, showing no avoidance of these cadavers by adult Colorado potato beetles. The likelihood that emerging adultswould contact infective cadavers on the soil surface was quantiÞed at different cadaver densities. A curvilinear relationship (y 4.8313x) best describes the frequency of encounters of adults as a factor of increasing density of cadavers on the soil surface. Mortality of adults and production of conidia on cadavers after encounters with increasing densities of infective cadavers had similar relationships that showthedecreased susceptibilityof adults toB.bassianacomparedwithprepupae.These relationships were used to model horizontal infection to emerging adults in the summer months, subsequent to a conidial spray targeted at larvae. The model indicates that horizontal infection of adults may potentially be signiÞcant (30Ð70% of horizontal infection), and that simulated early sprays targeted at Þrst-instar larvae resulted in the maximum levels of predicted horizontal infection.