|Scientific Name||Phyllonorycter blancardella (F.)|
|Common Names||English: Spotted tentiform leaf miner; German: Faltenminiermotte; Spanish: Minadora; French: Mineuse marbrée; Italian: Minatrice marmorizzata|
The adult has white streaks on its golden brown- and black-patterned, heavily-fringed wings that span 7 to 9 mm (0.27-0.35 inch); in flight, it looks shimmery. At rest, the moth is only 3-4 mm (0.12-0.16 inch) long.
The larva reaches a length of about 6-7 mm (0.24-0.27 inch). The sap-feeding instars have a yellowish-white, flat and legless body. The tissue-feeding instars are dark yellow or light brown, and their shape is that of typical caterpillars.
The larvae of P. blancardella feed inside apple leaves and thereby create their typical mines in the form of clusters of spots about 5 by 10 mm (0.19-0.39 inch) wide. Those of the first three, sap-feeding instars are visible on the undersides of leaves and are light green. When larvae have reached the fourth and fifth instars and have become 'tissue-feeding', their now whitish, transparent mines appear on the upper side, too. At this stage, the leaf becomes bent in the area of the mine, which mostly does not extend over leaf veins.
Each larva reduces the photosynthetically-active surface of a leaf by 4-5 %. In addition, the feeding injury affects the regulation of plant growth and fruit ripening.
Heavy infestations can cause leaf dropping and stunting: it will reduce both fruit quality and quantity, and may lead to less fruit setting in the following season.
In April and May, the adults emerge from overwintering pupae and mate shortly afterwards. Each female produces on average 25 (max. 150) eggs, which are laid singly on the undersides of leaves. After about a week, the larvae hatch, directly through the underside of the egg into the leaf tissue. There are two forms of larvae. The three younger, 'sap-feeding' instars feed by ripping-open cells in the spongy mesophyll only, and ingesting the sap. The two older, 'tissue-feeding' instars chew cells in all parenchymal tissues. Larval development lasts about 4 weeks, but sometimes considerably longer.
Pupation occurs inside the mine. If local climate allows another generation to be produced within the same year, the adults emerge after 1-3 weeks. In some areas, active moths can be found until November. For overwintering, the pupa remains in the leaf when it drops to the ground.
Depending on temperature, the reproductive cycle of P. blancardella lasts between one and three months. Typically, 2-4 generations occur per year, and they may overlap at the end of the season due to varying development rates.
P. blancardella originates from Europe, but it was introduced to North America in the 1930s.
Additional Crop Information
Apple; reports from other hosts very probably relate to other closely-related species that are easily mistaken as P. blancardella.
The degree of damage caused by this pest varies greatly between individual orchards. In many producing areas, the tentiform leaf miner is not considered a serious problem. However, in cases of heavy infestation, it can cause significant economic losses. Occasionally, sudden outbreaks occur, probably due to changes in orchard management.
Integrated Crop Management
Healthy trees sufficiently supplied with water and nutrients can tolerate infestation better. Water stress in particular aggravates damage by leaf miners.
Water stress in particular aggravates damage by leaf miners. Phyllonorycter blancardella is controlled by a large number of parasitoids and predators. If treatment becomes necessary, pesticides that spare beneficials are to be preferred.
Destroying leaves on the orchard floor (e.g. by raking and burning) in the autumn will significantly reduce overwintering leaf miner populations.
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