What can significantly affect the decomposition rates of a body?

The decomposition rates of a body are notably influenced by temperature and the presence of insects, making this the correct choice. Higher temperatures accelerate the biochemical reactions that lead to decay, while insects, particularly blowflies, play a critical role in breaking down tissue and facilitating decomposition. Insects are often among the first organisms to arrive at a decomposing body, and their activities significantly speed up the process. They not only consume the organic material but also lay eggs that hatch into larvae, further contributing to the breakdown of tissues.

When examining the other options, time of year can have an impact on decomposition, but it is not as direct or significant as the combined effects of temperature and insect presence. The deceased's diet may influence the composition of the tissues and some factors of decomposition, but it is not a primary driver of the decomposition process compared to environmental factors. Lastly, moisture levels can affect decomposition, but focusing solely on moisture levels in isolation overlooks the critical roles that temperature and insects play.