The Mexican Bean Beetle (Epilachna varivestis) is a common pest on beans. It is from Mexico, but has been found in many other locations. They can be very challenging to control, and different insecticide products may target different life cycle stages (eggs, nymphs, adults) and not affect the pest at the other life cycle stages. For this reason, predicting when different life cycle stages will occur, based on current observations and weather data, can be very helpful. Researchers have developed a growing degree day model for Mexican Leaf Beetle to help predict when different life cycle stages will occur.

Calculating Growing Degree Day Units

The Mexican Bean Beetle growing degree day model uses a lower threshold of 11.5C for calculating growing degree day units. The growing degree day units can be calculated from daily maximum and minimum temperatures using these thresholds, or by using the Pest Prophet app, which features this model and is easy to set up and use.

Setting the Biofix date

In order to begin growing degree day accumulation, first a “biofix” date must be set which is the first date, after which growing degree day units will begin to accumulate. In the Pest Prophet app, the biofix date can be adjusted for any observed life cycle stages.

For the Mexican Bean Beetle model, the biofix date should be set when the first generation of adults, or eggs are observed. Approximately 69 GDD(C) after the biofix date (when eggs are observed), larvae will be observed. Approximately 270 GDD(C) after the biofix date (when eggs are observed), larvae will be observed. At approximately 360 GDD (C) the next generation of adults will be observed.

Sources:

Cardenas, S. A., H. B. Mojica and R. R. Robles. 1978. Estudios bioecologicos de Epilachna varivestis Mulsant, bajo condiciones de laboratorio y campo. Agrocienca 34: 133-145.