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Abstract
The main scale insect pest in citrus orchards in Northland, New Zealand was Ceroplastes destructor although C. sinensis was more widespread. We studied the phenology of both species over 3 years by regularly sampling scales on leaves and wood for laboratory examination. Both species were univoltine. The start of C. destructor crawler emergence varied by c. 7 weeks o ver 6 years, and was inversely correlated with annual degree‐days. Egg hatching occurred c. 2 months earlier in C. destructor than C. sinensis. The development of successive instars continued to be earlier in C. destructor so it passed through the first and second instar stages by autumn and 4 months faster than did C. sinensis. First and second instars are vulnerable to adverse weather and predation and their longer duration in C. sinensis may partly account for its lower abundance. We predict that control by insecticides should be most effective in late January for C. destructor and in late March for C. sinensis.
