Temperature effects on the susceptibility of the Colorado potato beetle (Coleoptera : Chrysomelidae) to Beauveria bassiana (Balsamo) vuillemin in Poland, the Czech Republic and the United States

Beauveria bassiana (Balsamo) Vuillemin is a fungus with broad spectrum inse cticidal activity. As a biological control agent used against Colorado pota to beetles (Leptinotarsa decemlineata (Say)), this fungus has performed err atically in various field studies. This inconsistent performance has been a ttributed to formulation problems, UV sensitivity, and humidity. In a multi -site test, B. bassiana controlled Colorado potato beetle larvae in both Po land and the Czech Republic, but not in Maryland. Control was measured by r eduction in populations of beetle larvae. One of the major differences amon g these sites was temperature. In Poland, the mean temperature ranged from 5 degrees C to 23 degrees C; in the Czech Republic the average temperature ranged from 6.7 degrees C to 18.7 degrees C; and in Maryland, temperatures at time of application exceeded 45 degrees C at canopy level. This led us t o examine B. bassiana growth in vitro. While B. bassiana grew in the labora tory from 16 to 30 degrees C, the B. bassiana from a formulated product (My cotrol(TM), Mycotech, Butte, MT) did not germinate at temperatures above 37 degrees C. Germination and subsequent development of this entomopathogenic fungi are critical factors in the infection and control of the Colorado po tato beetle. As a consequence of the inability to germinate at high tempera tures, B. bassiana would not be expected to effectively control pest insect s in climates with hot summers. This fungus, however, may be suitable for i nsect control in early spring or in cool temperature climates during the gr owing season.