Three-way interaction between biological control insects, a congener and their shared parasitoid: Evidence of biotic resistance

Authors: Smith, Melissa; Tipping, Philip; Minteer, Carey; Berro, Alissa; Rice-David, Karen; Lake, Ellen

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Biological control organisms sometimes fail due to adverse interactions with the native community, such as parasitism. In Florida, biological control organisms for Eichornia crassipes, Megamelus scutellaris, are attacked by native mymarid parasitoids. We utilized a series of ponds to conduct experiments to detect parasitism rates on biological control insects from native parasitoids and whether these not only directly affect biological control 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 indicates that rather than provide an augmentive subsidy to the parasitic wasps, Megamelus scutellaris is experiencing biotic resistance from these native parasitoids when in close, closed positions.

Technical Abstract: Invasive plants are one of the strongest drivers of species extinctions. Weed biological control offers a sustainable and safe means of long-term population reduction of their target. Herbivores introduced for the control of invasive plants interact with the native community in addition to the top-down control they exert on their host plant. Frequently this results in their reduced efficacy, but they may also interact in non-direct pathways such as apparent competition between shared parasitoids. Water hyacinth (Eichornia crassipes) is one of the worst invasive plants worldwide and clogs many of Florida’s waterways. Large-scale invasions impede travel by boats and aquatic vertebrates and provides stagnant water that provides habitat for Aedes mosquitoes. Megamelus scutellaris (Hemiptera: Delphacidae), a leaf hopper, was introduced in 2013 for the control of water hyacinth. Within aquatic habitats, M. scutellaris encounters a native congener, M. davisi that lives on Nuphar lutea. Additionally, both species are attacked by a native egg parasitoid, the fairy wasp Kalopolynema ema (Hymenoptera: Mymaridae). To gauge whether M. scutellaris is providing a subsidy to K. ema resulting in the eventual decrease of M. davisi, we set up 1m x 1m plots of E. crassipes and M. scutellaris within ponds containing N. lutea, M. davisi and K. ema. We then measured parasite occurrence at 1m, 5m, 10m and 20m from E. crassipes for 12 consecutive months. We found no significant relationship between distance from E. crassipes and the incidence of parasitism in M. davisi. Kalopolynema ema readily switched and utilizes M. scutellaris. Our data indicate that biotic resistance from K. ema likely reduces M. scutellaris populations where they co-occur with M. davisi rather than providing a subsidy.