Biological control food webs suggest biotic resistance not apparent competition

Authors: Smith, Melissa; LAKE, ELLEN - Mt Cuba Center; MINTEER, CAREY - University Of Florida; Tipping, Philip; RICE-DAVID, KAREN - Archbold Biological Station

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/10/2023
Publication Date: 6/10/2023
Citation: Smith, M., Lake, E., Minteer, C., Tipping, P.W., Rice-David, K. 2023. Biological control food webs suggest biotic resistance not apparent competition. Ecological Society of America Abstracts.

Interpretive Summary: We looked for evidence of apparent competition within a simple (waterhyacinth) and complicated (Old World climbing fern) food web system involving biological control. In both systems, we observed that biological control agents are readily integrated into the consumer resources for parasitoids and predators, resulting in possible checks on the biological control agent populations (although this was not explicitly tested). We did not, however, see a reduction in native herbivores (apparent competition through predation/parasitism) or increases in native parasitiods. In these two systems, the biological control agents are safe in terms of host specificity, but may face obstacles (biotic resistance) due to native predators.

Technical Abstract: Biological control of weeds involves the reunification of specialist herbivores with their co-evolved host plant, the target weed. A the primary criticism of the discipline is that indirect effects are not anticipated or tested during the pre-release period. While realistically testing these hypotheses would be virtually impossible during the quarantine faze of a biological control project, we aimed to retrospectively investigate indirect effects within the adventive community in the form of indirect competition between shared parasitoids. We tested this hypothesis in two systems, one with only three constituents and another with multiple shared host species and parasitoids: waterhyacinth (Pontederia crassipes) and its biological control agent, Megamelus scutellaris, and Old World climbing fern (Lygodium microphyllum, hereafter OWCF) and its biological agent, Neomusotima conspurcatalis. In each system we exposed all susceptible life stages of the hosts to naturally occuring parasitoids. We observed parasitism rates over two full years in naturally occurring populations of both the biological control agents and their native congeners or analogs. In the waterhyacinth system, we measured the emergence of the fairy wasp, Kalopolynema ema in enclosed cages with either Megamelus scutellaris (biological control) or Megamelus davisii (native congener with host Nuphar lutea). In the OWCF system, we collected naturally occurring biological control moths (N. conspurcatalis) and native analogs (i.e., Lepidoptera from related families of similar size and life cycle) and reared them out until adulthood or until parasitoids emerged from a collected egg, larva, or pupa. In both systems, we found no significant evidence of subsidy to the native parasitoids. Rather, we found that the parasitoids had little effect on the native species and had a negative impact on the biological control agents when present. Evidence from these two systems suggests that biological control agents are far more likely to experience spillover and biotic resistance from parasitoids than provide a subsidy to these native parasitoids sufficient to impact native host populations.