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 hatch, the larva can adjust its temperature by moving up and down in the soil column.
The eggs must hatch before soil temperatures cool At temperatures below 13, no development of the embryo occurs and no larvae. Temperatures above 34 C are lethal. The beetle must spend the winter in the soil below the freeze zone as a larva. Overwintering as an egg is not possible because eggs are unable to withstand the cold winter weather.