Eliminating the pesky fruit flies
by Junelyn S. de la Rosa
Native to the Philippines, the oriental fruitfly (Bactrocera Philippinensis) is a very destructive pest to edible fruits like mango, guava, breadfruit and papaya.
Eradicating the fruit fly using bait control could be done in two stages using the Male Annihilation Technique (MAT) and the Sterile Insect Technique (SIT). First, the researchers reduced the population of male oriental fruit flies to a minimum so that mating would not occur. Male oriental fruit flies were trapped using methyl eugenol- a powerful male attractant, with an insecticide such as Naled (Dibrom) or Fipronil.
Cordelitos (lengths of 6-ply cotton string about 30-45 cm) or caneite (compressed fibreboard) blocks (50 mm x 50 mm x 12.7 mm), or coconut husk blocks (50 mm x 50 mm x 10 mm) were soaked in the bait material and distributed in the field at 400 pieces per square kilometer. This treatment was repeated every eight weeks. The baits were placed on top of tree trunks or wooden poles, well out of the reach of children or animals. This technique is called the Male Annihilation Technique (MAT).
Then the residual fruitflies were eradicated using the Sterile Insect Technique (SIT) or the sterile male technique. Sterilizing insects is a new technique where insects are either treated chemically, genetically, or with radiation to be infertile. In the case of male fruit flies, they are subjected to radiation to make them sterile. The method aims to wipe out the fly population by introducing sterile males that cannot produce any offspring when they mate with the female fruit flies.
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 skin damage to the fruit did result. To counter this problem, the United States Department of Agriculture (USDA) developed a genetic technique that separates males from females in several fly species. Flies released in Hawaii were only male sterile flies.
To ensure that SIT works, 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.
Another biological control method against fruit flies is the establishment of parasitoids such as Fopius arisanus (Sonan) which is specific to the oriental fruit fly. 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. Since they are fairly specific to certain fruit fly species or genera, parasitic wasps can be effective for fruit fly control.
For example, when these wasps were introduced in Hawaii, scientists documented that the Mediterranean fruit fly population was reduced to less than half.
Parasitoids do not eat or sting fruit. They lay their eggs in fruit fly larvae that are developing in fruits that have already been damaged by fruitflies. Therefore, parasitoids have no damaging effect on the fruit that is not yet infested with fruit fly eggs or larvae.
Today, only Guimaras is capable of meeting strict export standards of developing countries. Only Guimaras has successfully implemented an integrated pest management program for fruit flies. Scientists are still crossing their fingers that other regions in the country will follow suit and learn to successfully manage the fruit flies and cut the losses in our fruit industry.
Source: Swarming, Delayed Sexual Maturation of Males and Mating Behavior of Fopius arisanus (Sonan) by Gorgonio Quimio and Gimme H. Walter at Tel. No. (094) 536-2409 and Biological Control Against Fruit Flies in Pacific Island Countries and the Territories