The Japanese Beetle is a scarab beetle that is a widespread and destructive pest on a variety of hosts. Typically adults feed on leaves, and the larvae, a white grub, feed on roots.

Japanese Beetle Life Cycle Stages

Japanese Beetles usually take one year to complete a generation. Japanese Beetles overwinter as third instar larvae in the soil, and resume feeding activities spring or late winter. These larvae then pupate and adults emerge in late spring or early summer. Adults feed on a variety of sources, depending on location, before depositing eggs in the soil.

The period of adult emergence is key for insect prevention, both for placing traps and for using insecticides, if necessary. Researchers have created the Japanese Beetle Adult Emergence Growing Degree Day Model to better predict when the adults will emerge from the soil.

Calculating Growing Degree Day Units

The Japanese Beetle Emergence Growing Degree Day model uses a lower threshold of 50F and an upper threshold of 100F. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

Using Jan. 1st as a default “biofix” date, or starting point for accumulation, the first adult emergence occurs at approximately 971 GDD (F). However, it is recommended to place traps at approximately 921 GDD (F) in order to catch the first adult emergence. After adults are caught consistently, control measures should be taken.

Source:

Magarey et al. 2007. NAPPFAST: An Internet System for the Weather-Based Mapping of Plant Pathogen. Plant Disease. April 2007, Volume 91, Number 4 Pages 336-345