Impact of Biochar on Douglas-Fir Tussock Moth (Orgyia pseudotsugata Lepidoptera: Erebidae) Larvae Reared on Synthetic Diet

SIMPLE SUMMARY: The novel use of carbon-rich biochar as a soil amendment in forest systems may be beneficial in the restoration of disturbed sites due to its ability to increase soil water holding capacity, potentially reduce drought stress in surrounding vegetation and aid in long-term carbon sequestration. As biochar is utilized in forest management, it is necessary to establish the potential effects that it may have on insects and other invertebrate assemblages. The results of recent laboratory studies demonstrate a potential for negative impacts on insects. Examining direct exposure of insects to biochar in a laboratory experiment may help us understand what effects biochar may have on insects that come into direct contact with the material. Along with direct exposure, biochar applications in the field would result in the surface and possible contamination of insect nutrient sources. To determine the impacts of ingesting biochar, we reared Douglas-fir tussock moth, Orgyia pseudotsugata, on synthetic diet to examine the insect’s survival and longevity. ABSTRACT: The use of biochar as a soil amendment in forest ecosystems can be beneficial in the restoration of degraded soils. Forest insects such as the Douglas-fir tussock moth, Orgyia pseudotsugata (McDonnough) (Lepidoptera: Erebidae), may be exposed to biochar when the material is applied. Two experiments were conducted using biochar either (1) applied to the surface of the diet at three rates (0, 5, and 10 mg) or (2) incorporated into synthetic diet at four rates (0, 10, 20, and 40% volume/volume). The objective of both experiments was to determine if biochar on the surface or incorporated into a synthetic diet affected development and survival of O. pseudotsugata larvae. In both experiments, there was a significant decrease in estimated time to larval mortality in all biochar treatments compared to untreated controls. In the surface-applied biochar experiment, there was a significant difference in larval weight gain at day 12 between the control and 10 mg biochar treatments. In the experiment with biochar incorporated into the diet, mean larval weight at day 12 was highest in the low (10%) biochar treatment compared to all other treatments, although weight gain was only significantly different between the low- and high-concentration (40%) biochar treatments. Our results suggest that larvae, feeding on a low amount of biochar in the synthetic diet, may respond by engaging in compensatory feeding behavior. Fewer surviving larvae in the biochar treatment groups may contribute to the lack of significance found in the comparison of weight gain at day 24 in each experiment.