What are parasitoids?
A parasitoid is defined as an organism that is parasitic in the immature stage and free-living as an adult. Fruit fly parasitoids are insects that develop by laying their eggs in fruit fly eggs or larvae. The host is killed when the parasitoid's larval development is completed. Parasitic wasps were introduced and established for fruit fly control. They are fairly specific to certain fruit fly species or genera.

Are there any parasitoids in Hawaii?

The important fruit fly parasitoids currently established in Hawaii are Fopius arisanus, F. vandenboschi, Diachasmimorpha longicaudata and D.tryoni (hosts are Oriental and/or Mediterranean fruit fly) and Psyttalia fletcheri (host is melon fly). Other, less effective parasitoids also are present. Exploration for effective, new parasitoid species is ongoing at UH and HDOA. Some work is being conducted by the Biological Control division of the Hawaii Department of Agriculture under a grant provided by the USDA Agricultural Research Service.

What is the Sterile-Insect Technique ?

The sterile-insect technique (SIT) has been successfully used to eradicate fruit flies in many parts of the world. Also referred to as the sterile male technique, male fruit flies are sterilized and then release into the wild where mating with fertile "wild" females result in infertile "sterile" eggs being laid. In the fruit flies, the preferred method of sterilization is radiation. The method aims at flooding a field population with sterile males. The result of this sexual encounter of sterile with wild insects is that no progeny are produced.

What are sterile insects?

Sterile insects are treated chemically, genetically, or with radiation to be infertile. In the fruit flies, the preferred method of sterilization is radiation. The flies survive this treatment and are released in the environment to breed with wild flies. The result of this sexual encounter is that no progeny are produced.

How do sterile insects and parasitoids suppress fruit flies?

Sterile insects are employed to compete with wild males flies to reduce the number of fertile mating events, to cause female flies to lay infertile eggs. To assure success, sterile insects must be present in much greater numbers than the fertile wild male flies in order to reduce production of progeny. The method is only effective after the fly population has been greatly reduced by other means, because it only takes one fertile, male fly to inseminate a number of female flies.

Parasitoids help reduce the overall population of flies by insuring that a proportion of the fly progeny will be killed and ultimately develop into parasitic wasps instead of flies. For example, when these wasps were introduced to Hawaii, scientists documented that the Mediterranean fruit fly population was reduced to less than half of what existed before the releases.

Both biological control practices are advantageous in that the sterile insect and parasitoid are naturally programmed to search out the target pest. Parasitoids and sterile insects have advantage to go into the areas where the other techniques cannot be applied.

Can sterile insects and parasitoids sting my fruits and vegetables too?

Sterile flies have been used in many countries. In the past, both male and female flies were released. Sterile female flies’ eggs did not develop, however, some cosmetic damage to the fruit did result. To counter this problem, the USDA has developed a genetic technique that separates males from females in several fly species. Flies that will be released in Hawaii will be only male sterile flies.

Parasitoids do not eat or sting fruit. They lay their eggs in fruit fly larvae that are developing in previously stung fruit. Therefore, parasitoids have no damaging effect on the fruit that has not already been infested with fruit fly eggs or larvae.