[Aim]  To clarify the occurrence and distribution of Panaphis juglandis in the Juglans sigillata producing area of Baoshan in Yunnan Province, to assess the damage caused by this pest, and identify potential biological control agents for it. [Methods]  Five stands of J. sigillata in Baoshan, Yunnan Province were surveyed to determine the population density, infestation rate and spatial distribution pattern of P. juglandis, and the number and species of predatory ladybugs. The predatory responses, search effort, density and intraspecific interference responses, of different developmental stages of the dominant ladybug species to P. juglandis were measured under laboratory conditions. [Results]  P. juglandis had an aggregated distribution with infestation rates ranging from 26.67% to 93.33%, and population densities ranging from 10.27 to 489.41 ind./100 leaves. The dominant predatory ladybug was Calvia muiri, with a species dominance index of 44.34%. The predatory functional responses of different developmental stages of C. muiri to P. juglandis conformed to the Holling-Ⅱ functional response type; average daily predation increased with prey density. 4th instar C. muiri larvae had the highest instantaneous attack rate (a′) and predation capacity (a′/T_h) (1.321 5 and 197.24, respectively), and female adults had the maximum theoretical daily predation (1/T_h) rate of 153.85. The shortest processing time (T_h ) for a single prey was 0.006 5 d, and 1st instar larvae had the lowest predation capacity of 47.19. The search effort of different developmental stages of C. muiri decreased with increasing prey density, and was strongest in 4th instar larvae. The predation capacity of different developmental stages of C. muiri was strongly affected by its own density; at a given prey density, the intraspecific interference coefficient ranged from 0.596 1 to 0.733 2. When the predator-prey density increased in an equal ratio, the intraspecific disturbance coefficient ranged from 0.337 3 to 0.509 8. [Conclusion]  C. muiri is the dominant ladybug in J. sigillata forests in Baoshan and an important predator of P. juglandis. It should therefore be protected and utilized as a biological control for this pest.