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 decemlin eata (Sa)), was studied under both laboratory and field conditions. Fa ctors studied were temperature, number of P. bioculatus nymphs release d, their nymphal stage, and physiological age affecting satiety level. As temperature exceeded 19 degrees C under a sine wave fluctuating te mperature regime in the laboratory, dispersal of 2nd and 4th instars s trongly increased. Nymphs of the 4th instar were more mobile and dispe rsive than those of the 2nd instar. Nymphs of both stages departed fro m a release point on potato foliage in approximately half the time whe n released singly than in groups. Fourth instars showed a reduced tend ency to aggregate compared with 2nd instars, resulting in 3 times earl ier dispersal. Variation of physiological age within the Ind and 4th n ymphal stages for nymphs with unlimited access to prey showed that old er (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 pr esumably 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 ag e on dispersal.