Alder sawfly

Systematic position: Hemichroa alni (Linnaeus, 1758) belongs to the order Hymenoptera and the family Tenthredinidae. This insect is widely recognized as a specific defoliator that focuses its life cycle on alder tree species, playing a significant role in forest ecology.

Host plants: The primary hosts are species of alder (Alnus), particularly black alder and grey alder. While these are the preferred sources of nutrition for larvae, the insect is occasionally observed on birch trees when population densities are high or host availability is limited.

Biology and life cycle: The lifecycle of Hemichroa alni consists of the egg, larval, pupal, and adult stages. Females oviposit into the leaf tissue. After hatching, the larvae go through several instars, feeding voraciously on leaves throughout the summer months. Pupation typically occurs in the soil or leaf litter, where the insects overwinter inside durable cocoons.

Damage and pest status: The larvae are responsible for significant defoliation. In the early stages, they perform skeletonization of the leaves, while later instars consume the entire leaf lamina except for the main veins. This feeding pattern causes significant stress to the tree, reducing its ability to photosynthesize and survive environmental fluctuations.

Control measures: Management of the alder sawfly focuses on integrated pest management practices. Sanitation, such as removing heavily infested leaf litter, can help reduce the population for the following year. Chemical control using registered insecticides is recommended when larval activity reaches threshold levels, ensuring timely application during the early larval development stage.

• Regular field monitoring during the larval feeding season.
• Biological control through the use of entomopathogenic fungi or bacteria.
• Application of selective insecticides to minimize impact on beneficial insects.