Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2004
Publication Date: 1/15/2005
Citation: Johnson, M.T., Follett, P.A., Taylor, A., Jones, V.P. 2005. Impact of biological control and invasive species on a non-target native hawaiian insect. Oecologia 142: 529-540.
Interpretive Summary: Nontarget effects is a contentious issue for conservationists in the practice of biological control. Natural enemies attacking the native koa bug were examined to determine the importance of purposefully-introduced biological control agents and invasive species as sources of mortality. Koa bug is attacked by two biological control species, Trichopoda pilipes and Trissolcus basalis, which were introduced against the stink bug pest Nezara viridula, but accidentally introduced enemies were more important sources of mortality. Retrospective analysis of past biological control programs will provide useful information for designing future pre-release tests.
Technical Abstract: The potential for classical biological control to cause unintended harm to native species was evaluated in the case of the endemic Hawaiian koa bug, Coleotichus blackburniae White (Hemiptera: Scutelleridae), and parasitoids introduced to Hawaii for control of southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae). Parasitism and survival of C. blackburniae were quantified across its full elevation range (sea level to 2000 m) and host plant range (the natives Acacia koa A. Gray (Fabaceae) and Dodonaea viscosa Jacq. (Sapindaceae), and introduced Acacia confusa Merr.). Egg mortality due to the biocontrol agent Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) was low (maximum 17%) and confined to elevations below 500 m on the host A. confusa. Alien parasitoids in the genera Anastatus (Hymenoptera: Eupelmidae) and Acroclisoides (Hymenoptera: Pteromalidae) also attacked eggs at low levels (maximum 15%) below 900 m. Predation was a greater source of egg mortality (maximum 87%) than parasitism, and was significantly higher at low elevations and on the host plant D. viscosa. The alien spider Cheiracanthium mordax Koch (Clubionidae) and several alien ant species appeared to be the principal causes of egg mortality. Parasitism of adult female C. blackburniae by the biocontrol agent Trichopoda pilipes (F.) (Diptera: Tachinidae), was near zero at 21 of 24 sites surveyed bimonthly over one year on the island of Hawaii. Three sites had much higher levels of T. pilipes parasitism, totaling 17-30% among females (maximum attack 70%), 25-44% among males (maximum 100%) and 1-28% among fifth instars (maximum 50%). Parasitism by T. pilipes was density-dependent at the site level. Male-biased parasitism of adult C. blackburniae indicated that T. pilipes uses male aggregation pheromone for host finding, just as it does in N. viridula. The relative impacts of biocontrol agents and other sources of mortality were compared using life tables. Egg parasitoids, including T. basalis, had little impact on C. blackburniae reproduction. The tachinid T. pilipes showed potential for large negative impacts on populations at individual sites, but island-wide impacts appeared modest. Generalist predators of eggs had the greatest overall impact on koa bug populations. In retrospect, non-target attacks on C. blackburniae were predictable, but the magnitude of impacts would have been difficult to predict. Detailed pre-release studies of parasitoid host-finding behavior and koa bug life history could have yielded useful information regarding the interaction of C. blackburniae and T. pilipes