Latest Resistance management for sustainable agriculture and improved public health

San José scale

Comstockaspis perniciosa

San José scale (Comstockaspis perniciosa) is a polyphagous pest of deciduous fruit trees including apple, pear, peach, plum, currants; nut-bearing trees and some woody ornamentals. Comstockaspis perniciosa originated in Eastern Asia and has a global distribution due to accidental introductions. The lifecycle is completed in approximately 30 days, with development from two nymph stages, with the first instar referred to as crawlers, to prepupal (male only), pupa (male only) and adult. There can be one to five generations per year depending on location.  Adult scales are small (1-2mm) and are yellow or orange and dark gray in color.

Adults and nymphs feed on the bark of the tree and sometimes on the fruit. Damage symptoms can appear as discoloration on leaves and bark, dieback, lesions and growth inhibition. Crop loss is difficult to assess but overall, trees lose vigor and have a shorter lifespan.  Red spots on fruit are another sign of damage.

Once populations are established, San José scale can be difficult and expensive to control.  This is mostly due to the biology of the pest.  Treatment methods can range from fumigation of seedlings, foliar sprays of horticultural oil to smother overwintering stages and insecticides for the crawler stage.  Systemic insecticides can be used foliarly or applied at the base of the plant in the root zone.  While most insecticides are effective and have not shown cross resistance, resistance to some products exists.

There is no listed IRAC susceptibility test method available for scales


Aonidiella perniciosa
Aspidiotus perniciosus
Diaspidiotus perniciosus
Quadraspidiotus perniciosus



resistance profile

The first documented case of resistance to insecticides was reported in populations of Comstockaspis perniciosa in 1914. More recently, resistance has developed to organophosphates.

Species Distribution Chemical class Mechanisms
Comstockaspis perniciosa US Compounds of Unknown or Uncertain MoA (UN) Unknown
Comstockaspis perniciosa Australia Compounds of Unknown or Uncertain MoA (UN) Unknown
Comstockaspis perniciosa US Organophosphates (1B) Unknown
Comstockaspis perniciosa Chile Organophosphates (1B) Unknown

Key resources


Title Year Author(s) Publisher
Monitoring and Mechanisms of Organophosphate Resistance in San José Scale 140(7): 507-516 2016 Buzzetti K, Chorbadjian RA, Fuentes-Contreras E, Gutiérrez M, Rios JC, Nauen R Journal Of Applied Entomology
Resistance Management for San José Scale (Hemiptera: Diaspididae) 108(6): 2743-2752 2015 Buzzetti K, Chorbadjian RA, Nauen R Journal of Economic Entomology
Can Insects Become Resistant to Sprays? 7(2): 167-173. 1914 Melander AL Journal Of Applied Entomology

The information provided is based on literature reviews and as such IRAC cannot guarantee or be held accountable for the accuracy of the reports.

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