Neonicotinoids are widely known for their link to declining pollinator populations, but new research finds that the ill effects of these chemicals also extends to amphibian populations. In a study published late last month, scientists from the National Wildlife Research Center in Ottawa, Canada found that chronic exposure to real-world levels of the neonicotinoid imidacloprid limits the ability of juvenile wood frogs to escape a predator attack. This research adds additional evidence that neonicotinoids are harming aquatic food chains.
Researchers investigated the impact of neonicotinoids on the post-tadpole life stage of wood frogs, which has been identified as critical to sustaining viable populations of the species. Rather than determine acute impacts that assess how lethal a pesticide is, scientists opted to observe how wood frog behavior changes as a result of chronic, real-world exposure scenarios. In particular, scientists sought to figure out whether exposure resulted in an altered behavioral response to the presence of a predator.
As tadpoles, wood frogs were chronically exposed to real world levels of imidacloprid (1, 10, and 100 micrograms/liter), while others were left unexposed as a control. Three weeks after metamorphosis, these frogs were placed into 10 gallon tanks for observation. The tank was split into three sections, including a small pool, a gravel area, and an area with moss intended to act as shelter. A fabricated heron head and neck was used to mimic a predator attack, and researchers were able to observe the response from a viewer outside of the tank, without disturbing the frogs. Researchers observed whether the frog responded to the presence of the predator, how it responded, how quickly it moved, and whether it used shelter or refuge.
Wood frogs exposed to imidacloprid at 10 and 100 micrograms/liter are significantly less likely to actively respond to the attack by moving in any way (such as jumping or crouching) compared to unexposed control frogs. Frogs contaminated with imidacloprid are also more likely to remain in the area of the attack. While both control and exposed frogs use refuge in a similar way, researchers concluded that these results indicate neonicotinoids may make young wood frogs more vulnerable to predators. By impacting the ability for the frogs to assess and respond to the presence of a predator, neonicotinoids may be having subtle, but important, effects on frog survival.
Significantly, the impact of pesticides on animal behavior is not adequately studied, and often not considered by regulatory authorities. However, similar behavioral impacts are likely playing into neonicotinoid-associated declines with pollinator populations as well. In bees, these chemicals have been shown to interfere with foraging, memory, and learning.
Source: Beyond Pesticides, 15 Nov 18