Biological control remains an effective option for managing large-scale weed problems in natural areas. The predation or parasitism of biological control agents by other species present in the introduced range (biotic resistance) is well studied and is often cited as the cause for a lack of establishment of an agent, reduction of biological control efficacy, or for the eventual failure of a biological control program. However, the effects of a new subsidy provided by biological control insects for native parasitoids on native insects and communities have received significant theoretical attention, but very little quantitative evaluation. We initiated studies to investigate indirect effects of biological control agents on native analogues in two invaded habitats: Eichornia crassipes (water hyacinth) and Lygodium microphyllum(Old World climbing fern). Both species support large populations of the introduced natural enemies Megamelus scutillaris and Neomusotima conspurcatalis respectively. Native parasitoids now utilize both species as hosts. Mesocosms with all species were constructed to measure the density of native and introduced insects and the attack rates of parasitoids on each. Additionally, we monitored growth parameters of E. crassipes, L. microphyllum and native host plant species. Mesocosms with all species were constructed to measure the density of native and introduced insects and the attack rates of parasitoids on each. Additionally, we monitored growth parameters of E. crassipes, L. microphyllum and native host plant species.
Results/Conclusions
Initial measurements indicate that the presence of biological control insects affect population dynamics in native parasitoids in a predictive resource/consumer dynamic relationship. As biological control populations rise and, parasitoid populations rise and fall in response in both systems. We also observed potential effects of parasitoid spill back onto native analogous herbivores. Increased parasitism in native herbivores reduced attack on native host plants and increased growth in these species. Biological control insect populations could be altering community dynamics in favor of native plants at the cost of native consumers.