Oystershell scale parasitoid - Encarsia citrina

In this photograph, the scale beneath the wasp is oleander scale.

The wings of E.citrina are characterised by long delicate fringes which distinguish it from its close relative E. perniciosi.

Encarsia citrina was introduced to New Zealand accidentally. It was already known to be present in the country in 1923 when an attempt was made to supplement its effectiveness by introductions of further E. citrina from U.S.A. It was the most important natural enemy of oystershell scale in Canterbury in a 1959-60 study, in which it was found to parasitise mainly the second instar scale insects. It caused an average 40% parasitism from July to December, increasing from 10% in July to 85-100% in November. More male scales were parasitised than females, and from September a small percentage of parasitised adult scale insects were recorded (up to 17%). There was only one instance of a first instar scale being parasitised, and no parasitised male prepupae or pupae were found. E. citrina is an endoparasite, feeding within the soft body of its scale host. All the wasps are female and they lay 1-3 eggs in the second instar scales. Only one adult wasp develops fully from each host. E. citrina appears to be of limited occurrence in oystershell scale populations in Central Otago.