Jenise Brown
William A. Battaglin
Teagan A. McMahon
Rick A. Reylea
Jason R. Rohr
2017
<p><span>There are many examples where the use of chemicals have had profound unintended consequences, such as fertilizers reducing crop yields (paradox of enrichment) and insecticides increasing insect pests (by reducing natural biocontrol). Recently, the application of agrochemicals, such as agricultural disinfectants and fungicides, has been explored as an approach to curb the pathogenic fungus, </span><i>Batrachochytrium dendrobatidis</i><span><span> </span>(</span><i>Bd</i><span>), which is associated with worldwide amphibian declines. However, the long-term, net effects of early-life exposure to these chemicals on amphibian disease risk have not been thoroughly investigated. Using a combination of laboratory experiments and analysis of data from the literature, we explored the effects of fungicide exposure on<span> </span></span><i>Bd</i><span><span> </span>infections in two frog species. Extremely low concentrations of the fungicides azoxystrobin, chlorothalonil, and mancozeb were directly toxic to<span> </span></span><i>Bd</i><span><span> </span>in culture. However, estimated environmental concentrations of the fungicides did not reduce<span> </span></span><i>Bd</i><span><span> </span>on Cuban tree frog (</span><i>Osteopilus septentrionalis</i><span>) tadpoles exposed simultaneously to any of these fungicides and<span> </span></span><i>Bd</i><span>, and fungicide exposure actually increased<span> </span></span><i>Bd</i><span>-induced mortality. Additionally, exposure to any of these fungicides as tadpoles resulted in higher<span> </span></span><i>Bd</i><span><span> </span>abundance and greater<span> </span></span><i>Bd</i><span>-induced mortality when challenged with<span> </span></span><i>Bd</i><span><span> </span>post-metamorphosis, an average of 71 d after their last fungicide exposure. Analysis of data from the literature revealed that previous exposure to the fungicide itraconazole, which is commonly used to clear<span> </span></span><i>Bd</i><span><span> </span>infections, made the critically endangered booroolong frog (</span><i>Litoria booroolongensis</i><span>) more susceptible to<span> </span></span><i>Bd</i><span>. Finally, a field survey revealed that<span> </span></span><i>Bd</i><span><span> </span>prevalence was positively associated with concentrations of fungicides in ponds. Although fungicides show promise for controlling<span> </span></span><i>Bd</i><span>, these results suggest that, if fungicides do not completely eliminate<span> </span></span><i>Bd</i><span><span> </span>or if<span> </span></span><i>Bd</i><span><span> </span>recolonizes, exposure to fungicides has the potential to do more harm than good. To ensure that fungicide applications have the intended consequence of curbing amphibian declines, researchers must identify which fungicides do not compromise the pathogen resistance mechanisms of amphibians.</span></p>
application/pdf
10.1002/eap.1607
en
Ecological Society of America
A pesticide paradox: Fungicides indirectly increase fungal infections
article