T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Wasp (White butterfly pupal parasite) Pteromalus puparum

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
Subclass: Pterygota
Infraclass: Neoptera
Superorder: Endopterygota
Order: Hymenoptera
Suborder: Apocrita
Superfamily: Chalcidoidea
Family: Pteromalidae
Genus: Pteromalus
Species: Pteromalus puparum
Common name: Cabbage white butterfly pupal parasite

Pteromalus puparum is a tiny pteromalid wasp that was introduced into New Zealand between 1930 and 1934 as a biological control agent to attack the caterpillars of Pieris rapae (small white butterfly) and Pieris brassicae (great white butterfly) that feed on cabbages, native cresses and commercial and home brassica crops.
The adult wasps are 3-4 mm long and feed on flower nectar. Females are a shiny black, while males are a metallic greenish bronze and are normally smaller than the females. The wasps fly short distances of less than 25 mm which gives them the appearance of hopping.
This wasp parasitises caterpillars by injecting its ovipositor into the host and deposits anything up to 200 eggs inside. Sometimes eggs are laid into the prepupa. The eggs hatch into grubs which then devour the contents of the caterpillar. When mature they then pupate inside the host. The first adult chews a hole in the casing in the wing section of the host pupa through which most of the following adults will emerge. On an average 23 wasps emerge.
They mate immediately and then search for fresh pupae to infect.
A parasitised caterpillar becomes brittle and turns from green or grey to dull brown as the wasp larvae develop over about three weeks. An unparasitised caterpillar turns from green or grey to yellowish white as the butterflies inside reach maturity. The wasp’s mature larvae can overwinter within the host caterpillar. There can be four to five generations per year and each cycle takes from 20 to 30 days.

Pteromalus puparum has also played a significant role in suppressing the population of other non-target butterfly species such as of Bassaris gonerilla (Red admirals) and Danaus plexippus (Monarchs). The level of parasitism these species have never been quantified.

A diagram of an adult wasp (3-4 mm long).

A wasp laying eggs on a caterpillar

Newly emerged adult wasps.

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/