Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2002
Publication Date: 3/1/2003
Citation: Hight, S.D. 2003. Biology, host specificity tests, and risk assessment of the sawfly Heteroperreyia hubrichi, a potential biological control agent of Schinus terebinthifolius in hawaii. Biocontrol. 48:461-476. Interpretive Summary: Christmasberry is a South American tree that has invaded the drier sides of all the Hawaiian Islands. The tree is now classified as a noxious weed in Hawaii because it has become an aggressive, rapidly spreading plant that displaces native vegetation and forms dense monocultures that reduce the biological diversity of plants and animals. The plant cannot be economically or safely controlled with herbicides or cutting over the extensive areas that it now occupies. Scientists now stationed at the USDA Biological Control Center in Tallahassee, Florida evaluated the safety of introducing a leaf-feeding sawfly from Brazil into Hawaii to feed on Christmasberry. Biological control is the science of reuniting a foreign weed that is outgrowing the native plants in its new homeland with plant- feeding insects that attack the weed in its area of origin. Although studies in Brazil and Florida determined this insect was safe for release into Florida, it was essential to prove that the biological control agent not damage non-target Hawaiian plants. We evaluated the ability of the female sawfly to reproduce on 20 species of Hawaiian plants. All failed to support the growth and development of the sawfly except Christmasberry (70% survival) and a native Hawaiian sumac (1% survival). Without additional field studies, even this low level of risk was deemed too high to request introduction of the sawfly into Hawaii. Explorations for other, still more host specific biological control agents are being contemplated.
Technical Abstract: Heteroperreyia hubrichi, a foliage feeding sawfly of Schinus terebinthifolius, was studied to assess its suitability as a classical biological control agent of this invasive weed in Hawaii. No choice host-specificity tests were conducted in Hawaiian quarantine on 20 plant species in 10 families. Besides the target weed, adult females oviposited on four test species. Females accepted the Hawaiian native Rhus sandwicensis as an oviposition host equally as well as the target species. The other three species received dramatically fewer eggs. Neonate larvae transferred onto test plants successfully developed to pupae on S. terebinthifolius (70% survival) and R. sandwicensis (I% survival). All other 18 test plant species failed to support larval development. A risk analysis was conducted to quantify the acceptability of non-target species as host plants for H. hubrichi on the basis of the insect's performance at various stages in its life cycle. Risk of damage to all plant species tested was insignificant except for R. sandwicensis. Risk to this native plant relative to S. terebinthifolius was estimated at 1 %. Currently this level of risk is too high to request introduction of this insect into the Hawaiian environment. Detailed impact studies in the native range of S. terebinthifolius are needed to identify the potential benefit that this insect offers. Also, field studies in South America with potted R. sandwicensis would give a more reliable analysis of the risk this native Hawaiian plant would face from natural populations of H. hubrichi.