White grubs require three years to complete their life cycle and while it is possible to find all stages in any one year, the majority will follow a three-year pattern. In the past, outbreaks of white grubs have occurred every third year with the most severe damage caused by second-year grubs. At dusk, the adults congregate in large numbers to mate on trees which are isolated in large grassy areas or provide a silhouette effect near a large area of turf. Beetle activity occurs about the time hybrid-tea roses and catalpas are in full bloom. Very little feeding takes place, but the flights at dusk allow the beetles to mate.
Females then return to the surrounding turfgrass areas and deposit their eggs in the soil below.
The eggs require two weeks to hatch into small grubs, which feed near the surface. If moisture is not available, this process can be delayed by a couple of weeks. During periods of summer drought, grubs may remain deep in the soil where moisture is available. By the end of September, most of the grubs are at their mature size and begin to seriously damage the turf. Cool weather does not seem to deter them, as they will remain near the surface if there is adequate moisture until frost begins to drive them down in November or December.