Rearing and sampling methods for estimating spruce budworm development rates at constant temperatures

We describe an experimental protocol for measuring the response of spruce budworm post-diapause larval development to temperature. This protocol is specifically designed to include measurements of development near their upper and lower thermal thresholds. The application of this protocol to a laboratory colony allowed for the first experimental evidence that spruce budworm larval development occurs at temperatures as low as 5 ºC and as high as 35 ºC and provides data to estimate development rates at temperatures from 5–35 ºC in 5 ºC increments. Our protocol is also designed to minimize mortality near the thermal development thresholds thus allowing for multi-generational studies. We observed developmental plasticity in larvae reared at constant temperatures, particularly the occurrence of up to 42% of some individuals requiring only five instars to complete development, compared to the expected six instars. An occurrence that exhibited no clear relation to temperature. While this protocol is specifically designed for spruce budworm, it provides a template for the study of other species’ developmental responses to temperature.

Methods
Data collected from rearing of spruce budworm larvae at controlled temperatures in a laboratory. Methodological details are provided in the associated manuscript and readme file.