Pests > Pest Management > Biological control > Bioagents – insects > Erythina gall wasp > Erythina spp.; save the trees

Pests > Pest Management > Biological control > Bioagents – insects > Erythina gall wasp > Erythina spp.; save the trees

Pests Pest Management Biological control Bioagents – insectsErythina gall wasp Erythina spp.; save the trees

Erythina, how to save the trees?

September 2010. What can be done to save Erythina species before the introduction of the biocontrol agent. This challenge provoked a large response. One member said:

The Erythrinas in Fiji, northern Tonga and elsewhere are dying, both Erythrina variegata var. variegata and the indigenous var. orientalis. It is likely that the indigenous endemic species of Hawaii and New Caledonia are also affected. These trees are iconic. They are one of the most attractive street and ornamental trees; a very important nitrogen-fixing tree, particularly in Samoa; they are the sign of the time to prepare and plant yams, the chiefly crop of the past in many areas; they are used medicinally; parts are eaten in Papua New Guinea; they are important as living fencing; and they are among the most important sources of nectar for the Fiji lorikeet, the kula. They are dying in droves, in houseyard gardens, landscaping, and in shifting agricultural areas. They are also dying along the Lavena coastal walk in Taveuni.

The reason agriculturalists and pest people have probably not done anything about these deaths is because Erythrina has received a bad reputation as an alternate hosts for the fruit-piercing moth, which doesn???t not kill the trees, just ruins fruit for local sale or export.

Thus, a very important cultural and ecological tree is in danger of destruction, even extinction, if the gall wasp spreads and is not controlled. Is there anything that can be done NOW to save Erythrina, while waiting for the introduction of the biocontrol agent. It may already be too late!! Are insecticides a temporary solution?

Response from Samoa

The gall wasp has almost completely eradicated Erythrina variegata, which is the main host of Fruit piercing moth larvae in Samoa. From casual observations, the impact on other Erythrina spp. is negligible. But Samoa is yet to conduct an impact assessment of the wasp on the various Erythrina species and, indirectly, its impact on the FPM (population, field damage of fruits, etc.).

Erythrina trees have to be saved!

One suggestion was to establish arboretums or living natural museums in countries to protect the biodiversity and natural heritage.

Response from Tonga

The gall wasp is present in Tonga, but surprisingly the Erythrinia species have shown themselves to be hardy under attack by the gall wasp. This may be because the trees shed their leaves in the cool season (tropical autumn), helping to temporarily reduce the wasp populations.

Systemic insecticides would be effective in controlling the gall wasp, but is it worthwhile as applications would have to be on a regular basis, as re-infestation is bound to occur. Erythrinia is very easy to grow, thus making its recovery relatively easy once the gall wasp populations becomes more manageable.

On the biocontrol agrent, E eruythrinae

As for information on the biocontrol agent, it was reported that a few papers have been published in recent months, and reference to them is given below. The Hawaiian Department of Agriculture would be the best place for obtaining parasitoids. They have been looking at biocontrol of Erythrina gall wasp, and have released at least one species of parasitoid (the Eurytoma).

Gates, Delvare (2008) A new species of Eurytoma (Hymenoptera: Eurytomidae) attacking Quadrastichus spp. (Hymenoptera: Eulophidae) galling Erythrina spp. (Fabaceae), with a summary of African Eurytoma biology and species checklist. Zootaxa 1751: 1-24

La Salle et al. (2009) A new parasitoid of the Erythrina Gall Wasp, Quadrqastichus erythrinae Kim (Hymenoptera: Eulophidae). Zootaxa 2083: 19-26.

Prinsloo, Kelly (2009) The tetrastichine wasps (Hymenoptera: Chalcidoidea: Eulophidae) associated with galls on Erythrinaspecies (Fabaceae) in South Africa, with the description of five new species. Zootaxa 2083: 27-45. (abstract only)

The Hawaii Department of Agriculture has released Eurytoma erythrinae to control Quadrasticus on Erythrina. The main species infested were E variegata, E crista-galli, and the endemic E sandwicensis. The release was initially made in October 2008 and has successfully controlled the gall wasp. The gall wasp is no longer a serious problem and Erythrina trees are recovering throughout Hawaii. We are continuing with post release monitoring and will be finished this fall.

The natural enemy was discovered by Dr. Mohsen Ramadan (exploratory entomologist for the Hawaii Department of Agriculture) in Tanzania. Initial field studies were done in Tanzania, and specimens were brought back to the Hawaii Department of Agriculture containment facility for further studies. Eurytoma erythrinae was released following very rigorous host specificity studies on other gall forming insects found in Hawaii, and the completion of federal and state environmental assessments.

Introduction of E erythrinae to Pacific island countries

Samoa raised a word of caution about the introduction of E erythrinae. Although Hawaii did not find any of their native wasps parasitised by E erythrinae, it does not mean that it can be introduced into any other country based on the Hawaii tests. Importing countries would have to carry out their own host specificity tests against their endemic natural enemies before introductions are made. There may also be environmental differences Hawaii and other countries that reduce or negate the effectiveness of E erythrinae.