Jacobson's Geometer

Jacobson's Geometer (Erannis jacobsoni) is a member of the Geometridae family, order Lepidoptera, known for causing significant damage to various woody plants.

The species exhibits sexual dimorphism: males have fully developed wings for flight, while females are flightless, possessing only rudimentary wings or none at all.

The larvae, known as loopers, have a distinct movement pattern where they pull their hind legs toward their thoracic legs, creating a loop-like motion.

Caterpillars display cryptic coloration, usually ranging from yellowish-green to brown, allowing them to blend into the twigs and bark of their host trees.

Adult moths are nocturnal and typically appear in the late autumn, which is a defining characteristic of their biological cycle compared to many other pests.

This pest is a polyphage that primarily attacks fruit trees in the Rosaceae family, including apple, pear, cherry, and plum trees in commercial and private orchards.

The caterpillars are voracious eaters, initially feeding on the soft tissue of leaves and eventually skeletonizing them, leaving only the veins behind.

Significant infestations can result in complete defoliation of the tree, which severely stresses the plant and prevents normal photosynthesis during the growing season.

Beyond leaf damage, the larvae attack opening buds and young developing fruits, causing direct losses to the current season's crop yield.

Persistent infestations lead to a decline in tree vigor, making the plants more susceptible to fungal diseases, pests, and harsh winter conditions.

The life cycle of Jacobson's Geometer is unique because the moths mate and lay eggs during the late autumn months, shortly before the onset of winter.

Eggs are deposited in crevices of the tree bark or near branch buds, where they successfully overwinter until the warmer spring temperatures arrive.

Egg hatching is synchronized with the phenological stage of host trees, typically occurring when buds begin to burst in early to mid-spring.

The larvae spend the months of May and June actively feeding on the foliage, which is the most destructive period of their life cycle.

Once the feeding stage is completed, the caterpillars drop to the soil and pupate, remaining in a dormant state through the summer and early autumn.

The first indicator of an infestation is the appearance of small holes in young leaves, often referred to as "windowing" or "shot-hole" damage.

Inspecting the foliage early in the morning may reveal caterpillars stretched out along branches, where they remain perfectly still to mimic natural twigs.

Large amounts of fine silk webbing produced by the caterpillars on the tips of shoots or between leaves are a clear sign of their presence.

Heavy defoliation in specific parts of the canopy, where leaves look like transparent grids, often indicates a high population density of the larvae.

The accumulation of black, granular frass (excrement) on the leaves below the feeding sites is a reliable indicator that caterpillars are active in the canopy.

Sticky bands applied to tree trunks during the autumn are highly effective at preventing the flightless females from climbing up to lay eggs.

Cultivating the soil beneath the trees during the pupation period can destroy a significant portion of the overwintering population in the soil.

Chemical control involving systemic or contact insecticides should be applied at the first sign of egg hatching to minimize leaf damage effectively.

Biological control methods, such as the application of Bacillus thuringiensis based products, are effective at controlling young larvae while being safer for beneficial insects.

• Pruning and cleaning loose bark from trunks to remove potential overwintering sites.
• Encouraging the presence of natural predators like birds and predatory beetles in the orchard.
• Using pheromone traps for early detection of male moth flight patterns.