Grapholita molesta (Oriental Fruit Moth) - Fact Sheet

Background

Native to China and the Korean peninsula, where the peach tree is also native, the Oriental fruit moth was spread to many temperate fruit-growing areas of the world during the first thirty years of this century. The means of spread between countries was almost certainly as cocoons on dormant fruit-tree nursery stock, but spread within each country also occurred with infested fruit. This insect was first reported in the USA in 1916 and it rapidly spread throughout that country. It was first reported in Ontario in 1925. Today, the only commercial peach-growing area of North America which is free of the pest is the province of British Columbia. A small population was detected in 1957 and eradicated at great expense; annual surveys since 1957 have been negative for this pest.

Hosts

The principal host is Prunus ( peach, nectarine, apricot, plum, cherry). In Ontario, apple (Malus) and pear (Pyrus) have also be infested when they are grown in proximity to peach orchards. The pest has also been found on quince and almonds. Apples and pears are often heavily infested late in the season when larvae migrate to these fruits after peaches have been harvested. Other hosts are known.

Distribution

  • Asia: Armenia, Azerbaijan, China, Georgia, Hong Kong, Japan, Kazakhstan, North Korea, South Korea, Russia, Taiwan, Turkey, Uzbekistan
  • Africa: Mauritius, Morocco
  • Europe: Austria, Bulgaria, Czech Republic, Germany, France, Greece, Hungary, Italy, Malta, Moldova, Montenegro, Portugal, Romania, Serbia, Slovakia, Spain, Switzerland, Ukraine
  • North America: Canada (southern Ontario); USA all states.
  • Pacific: Australia, New Zealand
  • South America: Argentina, Brazil, Chile, Uruguay

Biology

This moth can produce up to six generations per year depending on the geographical region. In Ontario, up to four generations can occur each year. Mature larvae overwinter in cocoons. The cocoons are usually in the soil or in crevices under bark, or in old fruit containers or packing sheds. Pupation occurs in early spring and the first brood of moths appear when the peach is in blossom, with the peak of emergence occurring about the last week of May. The adult moth are generally weak fliers with average flights not exceeding 25 m, but flights of over 3 km have been reported for adults in search of a suitable host. When a host is found, eggs are laid on the leaves or on new shoots. In early June the newly hatched first generation larvae bore into the tips of terminal shoots and tunnel downward until they reach harder woody tissue, at this point they exit the shoot and enter another one. The tips of infested shoots soon wilt and die. A single larva may destroy two to five shoots before it matures. The mature larvae exit the shoots and drop via silken threads to the ground or the trunk of the tree, where they spin cocoons and pupate. Summer cocoons are more fragile than overwintering ones. The life cycle is repeated and the second brood larvae hatch between July 10 and 20. This generation also attacks shoots but by midsummer the new shoots begin to harden. At this time many of the partly grown larvae exit the shoots and attack the young fruit. They may tunnel to the pit or feed near the surface, producing large masses of gum mixed with sawdust-like castings (frass). Emerging larvae of later broods may bore into the soft stems of the fruit, being too small to attack the hard fruit directly. As the fruit ripens and softens it no longer produces gum when attacked and young larvae can enter it directly. Larvae that bore into the stems may tunnel down into the ripening fruit. Larvae of later broods attack the ripe fruit leaving no visual signs of infestation and it is not until the fruit is cut open that the larvae are discovered.

Detection & Identification

Symptoms

In late spring look for wilting shoots and die-back (fig. 3). Shoot injury will be conspicuous in heavily infested orchards. While this can be severe in nursery stock and young trees the main economic damage is the destruction of the fruit. In midsummer look for gum and sawdust-like frass on the surface of the green fruit. This may be seen near the stem or where two fruits touch. Late in the season the ripe fruit will show no signs of infestation.

Identification

Adults (fig.1) are small, dark grey moths with chocolate brown markings on the wings. Moths average 6 mm in length, with a wing span of about 1.3 cm. Males and females resemble each other, with the female being slightly larger. Eggs (fig. 2) when first laid are translucent white, slightly convex, measuring about 0.7 mm in diameter. Larvae (fig. 4) range in length from 1.5 mm for newly hatched larvae up to 12 mm for mature last instar larvae. There are 4-5 instars, all white in colour except the last, which is pink to almost red. Cocoons are constructed of silken thread and can be mixed with bark, peach pubescence, sand or leaves. Pupae are yellowish-brown, becoming reddish brown and turning black just prior to the emergence of the adult.

Adult
Figure 1
Eggs
Figure 2
Shoot die back
Figure 3
larva
Figure 4

Text: Plant Pest Surveillance Unit
Photos: Agriculture and Agri-food Canada, Research Branch, Ottawa

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