Modeling Exposure Risk and Determining Effects of Cholinesterase-Inhibiting Insecticides on Bats in Central California Agricultural Ecosystems

EPA Grant Number: F13C30656
Title: Modeling Exposure Risk and Determining Effects of Cholinesterase-Inhibiting Insecticides on Bats in Central California Agricultural Ecosystems
Investigators: Fraser, Devaughn Lee
Institution: University of California - Los Angeles
EPA Project Officer: Lee, Sonja
Project Period: September 30, 2014 through September 30, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Zoology


This research addresses several questions: What are bats in agricultural areas eating and what proportion of their diet consists of economically important agricultural pests? How are health and reproduction in freeranging bats affected by landscape-level insecticide use? What is the long-term trade-off, economically and environmentally, of using toxic insecticides that may be harmful to bats and other wildlife that provide important pest control services?


Bats are sampled while foraging in almond orchards located across a gradient of landscape-level insecticide-use applied to the surrounding 64-km2 area. Standard measurements include assessment of age and reproductive condition and a count of external parasites. Blood samples from two focal species, the big brown bat and the pallid bat, are analyzed for immune-response capabilities, and blood parasites are counted in blood smears. Prey DNA is extracted from guano and sequenced; coronavirus RNA is extracted from big brown bat guano and sequenced to characterize diversity and prevalence. On each night of capture, insects are sampled to assess dietary diversity and abundance relative to resource base. Acoustic monitoring stations characterize the relationship between pest abundance and bat foraging activity. Radio-telemetry tracks a subset of captured big brown bats to their roost locations to characterize their foraging range and behavior, and a maternity colony is monitored for emergence counts of the colony size and pre- and post-parturition. An exposure risk model is being developed based on insecticide residues detected on prey for a week following a spray. Combined with landscape level-analysis of ChE inhibitor applications and bat foraging behavior and dietary analysis, this model will predict exposure risk for multiple species of bats with differing foraging strategies (i.e., gleaning from ground or vegetation versus apprehending prey in the air).

Expected Results:

Broadly, chronic exposure to anticholinergic insecticides is expected to compromise immune function and reproduction in bats; high insecticide use is likely to limit resource availability to bats; and exposure risk will depending on a species’ prey preference and foraging strategy. The following specific findings are predicted: (1) Big brown and pallid bats captured in high-input areas (HIAs) will have higher prevalence and infection intensities of parasites and reduced constitutive immune capabilities, and they will be more frequently ChE-inhibited than bats in low-input areas (LIAs). (2) There will be a lower ratio of reproductive to nonreproductive females in HIAs, causing frequently exposed populations to have a lower annual growth rate than populations in LIAs. (3) Insect diversity will be lower in HIAs than in LIAs. Bat foraging activity and bat diversity also will be lower in HIAs. (4) The reduced dietary diversity in HIAs will lead to greater resource partitioning between sympatric species and between age-classes within species, potentially leading to species exclusion and lower bat diversity. (5) Pallid bats, which glean from vegetation and the ground, will have greater exposure risk than big brown bats, which catch prey in flight.

Potential to Further Environmental/Human Health Protection

Understanding bat activity around agricultural areas and the influence of pest control strategies on bat populations will guide management to maximize pest control while protecting insects’ natural predators and reducing the use of chemical pesticides. Quantifying exposure risk to bats will aid in EPA evaluations of risks to non-target wildlife. Furthermore, understanding the relationship between bat health and viral diversity for potentially zoonotic pathogens can help reduce this risk to humans by reducing the use of immunotoxic insecticides. Overall, this study addresses the ecological effects of insecticides on economically valuable insectivores and encompasses the three pillars of sustainability: the economy, society and the environment.

Supplemental Keywords:

agriculture, bats, insecticides

Progress and Final Reports:

  • 2015
  • Final