Monitoring populations of Galerucella birmanica (Coleoptera: Chrysomelidae) on Brasenia schreberi and Trapa natans (Lythraceae): Implications for biological control

In classical weed biological control programs, traditional choice or no-choice tests may reveal an insect's fundamental, but not its ecological host range. Although seldom quantified, the magnitude of interactions between the insect and the non-target plant species is an important consideration in the selection of biocontrol agents that demonstrate an ability to develop on non-target plants. An Asian leaf beetle, Galerucella birmanica is a potential biocontrol agent against water chestnut, Trapa natans, an invasive aquatic plant in North America. Water shield, Brasenia schreberi is a native aquatic plant in North America that is an occasional host of the beetle in China. The population growth and development of G. birmanica was monitored on B. schreberi for 7 months (up to six generations) under indoor caged conditions in China. The insect was able to sustain a population on B. schreberi, however, its population size was significantly smaller than that on T. natans, the usual host. After 4 weeks, beetle populations were 10 times lower on B. schreberi than on T. natans. On B. schreberi larvae developed more slowly and pupae and adults were smaller than on T. natans. The results show that G. birmanica will use B. schreberi but is unlikely to develop large, sustaining populations on this plant if it is introduced and released in North America, but this needs to be confirmed through additional field studies.