Alder sawfly

Systematic position. The alder sawfly Cimbex connata belongs to the order Hymenoptera, family Cimbicidae. This species is known for its robust appearance and is a significant, though often localized, defoliator of broad-leaved trees in temperate regions.

Host plants. The primary host for this species is the alder tree (Alnus spp.), including black and grey alder. While they are strictly associated with alder in most habitats, their presence is often tied to moist environments such as riverbanks, fens, and riparian forests where host trees are abundant.

Biology and life cycle. This pest completes one generation per year. Adults emerge in late spring. Females utilize their saw-like ovipositor to insert eggs into the leaf tissue. Larvae feed throughout the summer months. By late summer or early autumn, the mature larvae descend to the ground to spin a tough, parchment-like cocoon in the soil or leaf litter, where they overwinter.

Damage and pest status. Larvae are voracious leaf eaters. Younger instars create small holes, but older larvae consume entire leaves, leaving only the primary veins.

• Heavy infestation leads to severe defoliation.
• Stressed trees become more vulnerable to secondary pests like wood-boring beetles.
• Growth rates in young alder saplings may be significantly stunted.

Control measures. Management in forest stands focuses on biological control through the preservation of natural predators and parasitoids. In ornamental settings or nurseries, mechanical removal of larvae can be effective for small infestations. Chemical control should be reserved for outbreaks that threaten the survival of young trees, utilizing targeted insecticides during the larval feeding stage.