Walnut caterpillar

The Walnut caterpillar (Datana integerrima) is a moth species belonging to the family Notodontidae. It is recognized primarily as a defoliator that affects various hardwood trees, being a prominent pest throughout many regions of North America, particularly where walnut and pecan trees are cultivated on a commercial or residential scale.

The primary hosts for this insect include trees within the Juglandaceae family, such as black walnut, English walnut, and pecan. While these are the preferred sources of nutrition, the caterpillars have been known to feed on other species, which broadens the scope of potential damage in mixed plantings or diverse orchard landscapes.

The biology of Datana integerrima consists of a life cycle typically involving one to two generations per year. The insect overwinters in the pupal stage within the soil beneath host trees. In the spring and summer, adults emerge to mate and lay eggs in clusters on the underside of leaves. Newly hatched larvae remain clustered throughout most of their development stages.

The damage caused by the walnut caterpillar is classified as severe defoliation. Early-stage larvae perform skeletonization of the leaves, while older, more mature larvae consume entire leaf blades, leaving only the midribs and petioles. Significant infestations can lead to complete tree defoliation, which severely stresses the tree and can result in premature nut drop or reduced yield in subsequent years.

Pest management strategies should focus on integrated approaches. Key practices include:

• Monitoring canopy foliage during mid-summer for larval clusters.
• Physical removal of infested branches when feasible.
• Encouraging natural predators and parasitoids.
• Applying targeted insecticides or biological controls such as Bacillus thuringiensis during the early larval stages when the caterpillars are most vulnerable to treatments.