Jewel Wasp (Nasonia vitripennis)


    The small jewel wasp is parasitic on pupae of several fly species.  The adult female wasp oviposits within a fly puparium (the hardened larval skin which protects the fly pupa.)  The small, white, pear-shaped egg is deposited on the surface of the fly pupa in the space between the pupa and the puparial wall.  The jewel wasp is a gragarious parasite: more than one larva can complete development on a host.  Usually a number of eggs are deposited on each fly pupa. 
    The life cycle is relatively short.  At 77 degrees F, the average developmental time is about two weeks; egg, two days; white grub-like larva, about six days; and pupa, about six days.  At the end of this period, the adult wasp chews a small exit hole in the puparial wall and emerges.  Adults mate immediately after emerging and femalse begin to oviposit in a new fly puparia, if they are available.  Females which have not mated produce only males, while mated females can produce both females and males.  Progeny of mated females are usually about 80 to 85% female and 15 to 20% males.  In the mated female, the sex of the offspring is determined by whether or not sperm (stored in a special organ, the spermatheca) are released for fertilization.
    Occasionally one encounters mature (no longer feeding or growing) jewel wasp larvae which do not pupate.  These larvae have probably entered a dormant or resting stage called diapause.  Larval diapause in the jewel wasp is something which is relatively easy to prevent or, if desired, can be induced.  Diapause can be prevented by culturing the wasps at 79 to 86 degrees F. and by keeping the culture vials in total darkness (except for times of transfer).  Diapause can be induced by exposing dark female pupae or freshly eclosed females to a temperature of about 43 degrees F for three or more days.  Many of the offspring from treated females go into larval diapause instead of pupating.  Diapause can be broken by keeping the diapausing larvae for three months or longer at a temperature of 36 to 41 degrees F, then transferring them to room temperature.  After removal from refrigeration, all the larvae should pupate. 

Availability: These need to be ordered and will be available after spring break.

Housing: Jewel wasps require minimal space for rearing.  Large numbers of wasps can be cultured in glass vials or test tubes capped with foam or cotton-ball plugs.  Females will live for up to 45 days if well cared for.  To start a culture, put 10 or 11 female and 6 or 7 male jewel wasp pupae in a vial together.  Because the adult wasps are active, it is much easier to sex the wasps as pupae.  The female pupa can be recognized by the longer wings and the ovipositor which is seen as a pale ventral streak.  To obtain the wasp pupae, break open a parasitized fly puparium which is about 10 days old.  Use a probe or thumbnail to crack through the wall of the puparium.  By carefully separating the puparial halves, you should observe the wasp pupae attached to the outside of the fly pupa.  If wasp pupation has not occurred, simply place the halves of the fly puparium back together, replace the puparium in the vial, and wait for a day or two.  Newly formed jewel wasp pupae are white, gradually changing to a golden color within a day.  As white pupae are quite delicate, do not transfer them they have begun to darken.  As a pupa ages, the eye color begins to show, the thoracic region becomes a dark gray, and finally the entire body becomes uniformly dark.  Eclosion occurs approximately two days after the complete darkening of the pupae.  Maintain the culture vial containing sexed wasp pupae at 79 degrees F.  Add fresh host pupae when the adult wasps become active.  To add host pupae, tap the bottom of the culture vial against the palm of the hand.  This will jar the wasps to the bottom of vial and allow the experimenter to uncap the vial, drop in the fresh fly pupae, and recap the vial without wasps escaping.  To test whether fly pupae are young enough to be parasitized, crack open a puparium.  The fly pupa inside should be white-eyed or only slightly pink-eyed.  A fly pupa which has begun to turn dark gray is definitely not suitable.  If flesh fly pupae are being used as the host, place about the same number of fly pupae in the vial as female wasps.  If house fly pupae are used, about twice as many pupae should be supplied.  To obtain a maximum number of progeny, fly pupae can be replaced every day or two.

Food:
Jewel wasps can be easily reared on either house fly or flesh fly pupae.  Because the jewel wasp is gregarious, the larger flesh fly pupae allows for greater production of parasites per host than does a house fly pupa.  Adult female wasps feed on the host juices which exude from the wound made during oviposition (in fact, females may sting the host just to feed.)  However, providing honey (by streaking it on the side of the container with a needle) and water (using a wick or cotton ball placed in water) will increase adult longevity, especially the male's.