Japanese beetles in Indiana lay eggs in the soil in July and August when soil temperatures are warm. The embryos develop rapidly, larvae soon emerge and begin feeding before autumn arrives. Japanese beetle eggs are viable within a range of soil temperatures from 13 C to 34 C, typical of soil temperatures for Indiana in summer.
Eggs are laid in turf which shades the soil and provides evaporative cooling that keeps the soil temperatures in a tolerable range. Once the eggs…
Source: Living With Insects Blog