Identification of ice-nucleating active Pseudomonas fluorescens strains for biological control of overwintering Colorado potato beetles (Coleoptera :Chrysomelidae)
La. Castrillo et al., Identification of ice-nucleating active Pseudomonas fluorescens strains for biological control of overwintering Colorado potato beetles (Coleoptera :Chrysomelidae), J ECON ENT, 93(2), 2000, pp. 226-233
Laboratory studies were conducted to identify ice-nucleating active bacteri
al strains able to elevate the supercooling point, the temperature at which
freezing is initiated in body fluids, of Colorado potato beetles, Leptinot
arsa decemlineata (Say), and to persist in their gut. Adult beetles fed ice
-nucleating active strains of Pseudomonas fluorescens, p. putida, or p. syr
ingae at 10(6) or 10(3) bacterial cells per beetle had significantly elevat
ed supercooling points, from -4.5 to -5.7 degrees C and from -5.2 to -6.6 d
egrees C, respectively, immediately after ingestion. In contrast, mean supe
rcooling point of untreated control beetles was -9.2 degrees C. When sample
d at 2 and 12 wk after ingestion, only beetles fed P, fluorescens F26-4C an
d 88-335 still had significantly elevated supercooling points, indicating t
hat these strains of bacteria were retained. Furthermore, beetle supercooli
ng points were comparable to those observed immediately after ingestion, su
ggesting that beetle gut conditions were favorable not only for colonizatio
n but also for expression of ice-nucleating activity by these two strains.
The results obtained from exposure to a single, low dose of either bacteria
l strain also show that a minimum amount of inoculum is sufficient for esta
blishment of the bacterium in the gut. Persistence of these bacteria in Col
orado potato beetles long after ingestion was also confirmed using a polyme
rase chain reaction technique that detected ice-nucleating active bacteria
by virtue of their ina genes. Application of these ice-nucleating active ba
cteria to elevate the supercooling point of this freeze-intolerant insert p
est could significantly reduce their winter survival, thereby reducing loca
l populations and, consequently, crop damage.