The generation of fog oil smoke and maneuvers under obscurant cover are important components of troop training exercises at military installations. To comply with the Endangered Species Act, the impact of fog oil releases on avian threatened and endangered species (TES), or surrogates, have been evaluated in both field and laboratory studies. Although no direct acute effects on avian species have been observed, concern has been raised regarding a possible indirect impact via reduction in insect populations used as a food source for these species.
The objective of this project was to develop a methodology for quantifying population dynamics and food source value of insect fauna in areas subjected to fog oil smoke. The method is intended to provide reproducible exposures of insects to fog oil aerosols under various climatic and environmental conditions that duplicate chemical and droplet size characteristics of field releases of the smoke. The responses measured take into account reduction of food sources due to death and to changes in availability, palatability, and food quality of relevant life stages of insects that form the prey basis for the listed TES.
The study employed an environmentally controlled, recirculating wind tunnel outfitted with a high-heat vaporization and recondensation fog oil generator that has been shown to produce aerosols of comparable chemistry and droplet size distribution to those of field releases. The wind tunnel also supported canopy conditions needed for exposure realism, post-exposure revolatilization, and insect maintenance. Five species representative of major prey groups of the TES were assessed. To address potential differences in susceptibility of insect taxa to fog oil, the species were selected from different orders and included a geometrid moth, wood roach, mosquito, ant, and beetle. Assessments evaluated the impact of fog oil aerosols on a food resource rather than simply the toxic response of a class of organisms to the oil; therefore, the endpoints measured encompassed those that reduce not only numbers of prey but also the consumption of prey. Accordingly, post-exposure measurements assessed the following: (1) reduction in prey numbers through mortality of the consumed life stage (larvae, adult); (2) reduced hatch or emergence of the consumed life state; (3) reduction in prey availability because of impaired flight or decreased movement (reduced conspicuousness); (4) reduced palatability of contaminated prey; and (5) reduction in nutritional quality of prey.
The study provided a cost-effective method, as compared to field assessments, for quantifying the potential impact of fog oil on the food base of TES inhabiting Department of Defense lands where training activities are conducted. The method facilitates testing of prey species under relevant climatic and canopy conditions of specific TES. Because information on the effects of fog oil on important prey species of the red-cockaded woodpecker (Picoides borealis), several neotropical birds, and two endangered bat species were tested in this project, the exposure-response data from the study will directly benefit risk assessment and management efforts for these species. (Project Completed - 2007)