Factors affecting dispersal of Perillus bioculatus (Hemiptera: Pentatomidae), a predator of the Colorado potato beetle (Coleoptera: Chrysomelidae)

The dispersal potential of natural enemies is critical to the success of biological control by mass release. Movement of Perillus bioculatus (F.), a predator of the Colorado potato beetle, Leptinotarsa decemlineata (Sa)), was studied under both laboratory and field conditions. Factors studied were temperature, number of P. bioculatus nymphs released, their nymphal stage, and physiological age affecting satiety level. As temperature exceeded 19 degrees C under a sine wave fluctuating temperature regime in the laboratory, dispersal of 2nd and 4th instars strongly increased. Nymphs of the 4th instar were more mobile and dispersive than those of the 2nd instar. Nymphs of both stages departed from a release point on potato foliage in approximately half the time when released singly than in groups. Fourth instars showed a reduced tendency to aggregate compared with 2nd instars, resulting in 3 times earlier dispersal. Variation of physiological age within the Ind and 4th nymphal stages for nymphs with unlimited access to prey showed that older (and more satiated) individuals were less mobile than younger (and hungrier) ones. Physiologically more advanced nymphs within an instar formed larger and more stable groups than less mature ones, as they presumably were assimilating food and preparing for molting. Field tests with 2nd instars confirmed conclusions reached in the laboratory with respect to the effects of temperature, grouping, and physiological age on dispersal.