Japanese sawfly

The Japanese sawfly (Croesus japonicus) is a species of insect belonging to the order Hymenoptera and the family Tenthredinidae. This pest is native to East Asia and is known for its specialized feeding habits on specific hardwood tree species in forest ecosystems and urban landscapes.

The primary hosts of this species include trees from the Betulaceae family, specifically alders (Alnus) and birches (Betula). The larvae are considered significant defoliators, capable of rapidly consuming leaf tissue and significantly reducing the vitality of host trees if left uncontrolled.

The life cycle of the sawfly consists of four distinct stages: egg, larva, pupa, and adult. Females deposit eggs into leaf tissues, and larvae emerge to begin their feeding cycle. Development typically includes several larval instars before they descend to the soil or leaf litter to pupate and overwinter within protective cocoons.

The damage caused by Croesus japonicus is characterized by leaf margin feeding and complete skeletonization. Severe infestations result in significant defoliation, which causes physiological stress to the tree, reduces decorative value, and may increase susceptibility to secondary diseases or bark beetle attacks.

Effective management requires a combination of vigilance and timely intervention. Recommended protection strategies include:

• Regular inspection of host trees for egg clusters and early-stage larval colonies.
• Manual removal of damaged branches or infested leaf areas in small-scale plantings.
• Application of microbial insecticides, such as those containing Bacillus thuringiensis, to target larval stages.
• Implementation of soil cultivation techniques around the base of trees to disrupt the overwintering pupal stages.