Beauveria bassiana is more virulent against earlyversus
late-instar larvae of Colorado potato beetle
(Blonska, 1957; Fargues, 1972). A model developed by
T. Larkin, S. Galaini, and R. Carruthers (unpublished
in Galaini, 1984) predicted that B. bassiana would not
provide effective control of Colorado potato beetle larvae
when applied at weekly intervals. The reason for
this lack of control is because a 1-week interval under
normal field conditions would permit larval eclosion
and development to a more resistant stage (third instar).
Galaini (1984) demonstrated improved efficacy
from applications made on 3- to 4-day intervals compared
to 7-day intervals, but these tests were conducted
during different field seasons. Effects of changing
spray intervals have not been extensively examined
in directly comparable treatments.