|March 2008. An interesting observation from Samoa concerning the Erythrina gall wasp and its indirect effect on populations of fruit piercing moths.
It appears as if the gall wasp has had a large impact in Samoa. First, some species of Erythrina have been attacked and sometimes killed by the gall wasp; second, casual observations suggest that oranges and carambolas have been spared from damage by the fruit piercing moth in the last 2 years. These two fruits are now plentiful in the market.
In the past, there has been some discussion about destruction of Erythrina in Samoa in order to control the fruit piercing moth, but nothing was done.
Although it is possible that the gall wasp is having an impact on the population of Othreis fullonia by defoliating Erythrina variegata, there is also a need to consider the egg parasites which were introduced into the country in the late 80s and early 90s. Many of the eggs, perhaps 90%, are parasitised by either Telenomus or Ooencyrtus (and Trichogramma spp. are also present). So the decrease in damage by the fruit piercing moth may be due to a combination of effects.
The good news is that Erythrina subumbrans is very vigorous and can resist the gall wasp. E. subumbrans is a useful tree and is regarded as one of the most important legume tree in agroforestry, especially taro cultivation in Samoa.
Later, there was also mention that an effective control measure against fruit piercing moth in Samoa is to bag the fruit: nets are too expensive, and do not last long under local conditions (although a member said that those at Nafanua on carambola they have lasted 10 years). It was also said that in the western part of Savaii, people used to allow trees to overgrow orange trees to help hide the fruit from the moths. And another member said that the moths were now back (see photos above)!