A technique for transplanting gall-making insects: impacts on gall-maker and parasitoid larvae

Past studies of gall-maker-host interactions have been hampered by an inability to conduct experimental transplants of individuals between host plants. We describe a method for transplanting gall-maker larvae between galls on different individual host plants. Our method involves removing and inserting larvae through slits cut in young galls, and allows for healing and continuing growth of the gall. We developed and tested our method with larvae of the gall-making moth Gnorimoschema gallaesolidaginis Riley (Lepidoptera: Gelechiidae) on its two host plants, Solidago altissima L. and S. gigantea Ait. (Asteraceae). For three of four host × year combinations, unparasitized larvae survived at similar rates in transplants and controls. On one host in one year, transplant survival was low, possibly as a result of severe drought stress. Interestingly, survival of parasitized gall-maker larvae was lower in transplants for three of four host × year combinations, suggesting that gall-makers stressed by parasitoid attack are less able to tolerate transplant stress. Our technique may be applicable to many other gall-maker species, especially those making relatively thin-walled galls, and should represent a valuable new tool for the study of gall-maker-host interactions.