Indirect ecological effects in invaded landscapes: Spillover and spillback from biological control agents to native analogues

Authors: Smith, Melissa; Minteer, Carey; Lake, Ellen; Wheeler, Gregory; Tipping, Philip

Submitted to: Ecological Society of America (ESA)
Publication Type: Abstract Only
Publication Acceptance Date: 4/18/2016
Publication Date: 8/7/2016
Citation: Smith, M., Minteer, C., Lake, E.C., Wheeler, G.S., Tipping, P.W. 2016. Indirect ecological effects in invaded landscapes: Spillover and spillback from biological control agents to native analogues. Ecological Society of America (ESA). https://eco.confex.com/eco/2016/preliminaryprogram/abstract_59794.htm.

Interpretive Summary: Biological control organisms sometimes fail due to adverse interactions with the native community, such as parasitism. In Florida, biological control organisms for Lygodium microphyllum and Eichornia crassipes are attacked by native parasitoids. We constructed experiments to detect parasitism rates on biological control insects from native parasitoids and whether these not only directly affect biological insects, but also indirectly affect native host species by increasing parasitoid populations (i.e., spillover and spillback). Parasitoid populations and biological control populations closely follow each other and parasitoids are present when both biological control insects and their native analogs are present. The experiment has yet to detect whether or not parasitoids have a greater or lesser effect on native species in the presence biological control insects.

Technical Abstract: 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) invade large portions of the Greater Everglades Ecosystem. 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. 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. In pond studies with M. scutillaris and native Mymarid parasitoids, we have found all species present, but have yet to detect significant direct or indirect interactions. Initial surveys of native plants within Lygodium mirophyllum habitats reveal low native herbivore densities and no parasitoids. More time will be needed to identify interactions, if any, between native herbivores and their shared parasitoids with biological control insects.