|HALE, AAIMIE - HERITAGE UNIVERSITY|
Submitted to: Trends in Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2015
Publication Date: 12/5/2015
Citation: Neven, L.G., Hale, A. 2015. Use of scanning calorimetry and microrespiration to determine effects of Bt toxin doses on Pandemis leafroller (Lepidoptera: Tortricidae) metabolism. Trends in Entomology. 11:39-46.
Interpretive Summary: Bioassays to assess the effectiveness of insecticides by determining the insecticide dose and duration required to kill the pest are expensive and time-consuming. In an effort to reduce the time and cost of the assays, researchers at the USDA-ARS laboratory in Wapato, WA developed a method for assessing the metabolic effects of sub-lethal and lethal doses of the Bt toxin on an important pest of apples, the Pandemis leafroller. Using a differential scanning calorimeter, which measures the heat of metabolism of small organisms, in conjunction with measurement of respiratory gas production (CO2) and consumption (O2), she was able to determine that insect metabolism was greatly reduced after 1 day of exposure to lethal doses of the Bt toxin. The effects were more pronounced 2 days after the toxin challenge, even for the two lowest doses. Use of metabolic heat and respiration rates to assess the effect and ultimate fate of insects in biopesticide trials could benefit the research community, commercial biopesticide developers, EPA, and ultimately farmers by reducing costs and duration of testing new products.
Technical Abstract: Differential scanning calorimetry and microrespiration were used to determine the effects of the biopesticide, Bt toxin, on the metabolism of infected Pandemis leafroller, Pandemis purusana (Kearfott). The metabolic heat rate, CO2 evolution, O2 consumption of 2nd and 3rd instars following a 2 h exposure to different concentrations of Bt toxin on artificial diet from Day 0 to Day 3. Survival (mortality) was recorded from Day 0 to Day 4. The metabolic heat rates of the Bt challenged larvae were significantly lower than those of the untreated controls. CO2 evolution, and O2 consumption were not significantly different from one another, except for larvae challenged at the highest dose of Bt on Day 2. However, the calorespiromic ratios, kJ/mole O2 and kJ/mole CO2, of all Bt challenged larvae were significantly lower than untreated controls. The respiratory quotient, CO2/O2, was lowest for larvae challenged at the two highest doses. Mortality of the larvae followed a normal pattern, with the highest mortality at the highest doses and lowest mortality at the lowest doses. Differential scanning calorimetry can be useful in identifying larvae with compromised metabolism as a result of Bt exposure.