All of the studies include variables in a developmental curve of cold-blooded animals, so that as temps increase the development rate increases. It is reasonable that insects will develop faster at higher temperatures.
Egg state, first enstar stage, second enstar stage, third enstar stage--stages vary depending on temperature. All three studies are based on different temperatures.
Dusek: to get accurate estimation, you'd want to use the data from the closest temperature range, wouldn't you?
"Not necessarily." Doesn't matter. One can develop a number of thermal units as degree-hours or degree-days, and that number is remarkably constant, no matter what the ambient temperature is.