Oystershell scale - Life history

Oystershell scale populations live primarily on and under the bark of their host trees. This presents problems for control because it is difficult for insecticide sprays to reach the concealed insects. The adult female scale insects produce eggs (oviparous) which have a brief incubation period of from 15 minutes to 5 hours before hatching into mobile crawlers. This occurs under the scale of their mother, and the crawlers then disperse and settle on the bark and fruits. Male crawlers of the related species San Jose scale settle in greater numbers on leaves than the female crawlers but oystershell scale has not been recorded settling on the leaves. Crawlers are also carried by the wind and settle on other host plants. After settling, the young scale insects insert their long feeding stylets into the plant, where they feed on the phloem. In addition to this source of food, oystershell scale insects, like many other scale species, contain microorganisms which assist with their nutrition (endosymbionts). The first instar settled crawlers secrete a wax cap over their bodies which is initially white and then turns black. The cap hardens into a scale during this process and the scale insects become immobile. They then moult to the second instar (stage) with a grey scale and, while females undergo only one further moult before becoming adult, the males pass through prepupal and pupal stages before emerging as winged adults. The males back out of their scale cover during emergence and then live for 1-3 days. The longer-lived females continue to grow larger as adults. As in other parts of the world, the life cycle in New Zealand has only one generation per year and the winter is spent mainly as immature second instars.

The threshold minimum and the maximum temperatures for oystershell scale development in New Zealand are not known and no overseas data has been located.