Grapholita molesta
(Oriental fruit moth)

Adults of G. molesta can disperse locally by flight. International movement is likely to occur on fruit or plants for planting of host species, possibly in packing material.

The pest has, during the course of this century, spread from its east Asian origin to practically all the major stonefruit-growing areas of the world (Europe, North America, temperate South America, South Africa, Australia, New Zealand). It has therefore classically been viewed as a serious quarantine pest. However, the areas where it does not now occur (for example, northern Europe) are of marginal importance for the main hosts of G. molesta, and the risk of establishment is also rather marginal. So it is debatable whether G. molesta now presents more than a rather minor phytosanitary risk.

Phytosanitary measures

Normal inspection and phytosanitary certification procedures can be expected to exclude G. molesta.

The number of generations per year varies from four to six in the Black Sea region of Russia (Moiseeva, 1982), and depends on climatic conditions. In Italy, the flight of G. molesta normally begins in the second half of March. There are four to five distinct peaks of adult flight in April, June, July, August and September (Graziano and Viggiani, 1981). The adults of the first generation survive 30-40 days, compared with 11-17 in later generations (Enukidze, 1981). Egg deposition usually begins 2-5 days after the females emerge and continues for 7-10 days or longer. The eggs are laid singly and each female lays 50-200 eggs. In peach orchards, especially on young trees, most of the eggs are found on the under-surface of leaves near the tips of growing twigs. In quince and apple orchards the eggs are placed on the upper surface of the leaves (USDA, 1958).

G. molesta passes the winter as a full-grown larva in a cocoon. The cocoons are found in cracks and other rough places on the tree, under flakes of bark, under old bark wounds and in holes in twigs exposed by pruning. They are also found on the ground beneath infested trees, where they occur in the dried remains of fruits, in the stems of stubble and even in cracks of the soil. Early in the spring, at temperatures above 10°C, pupation takes place. The duration of the pupal stage averages 16 days, compared with a mean of 7 days in summer (Enukidze, 1981).

The larval development lasts 6-22 days, varying with temperature, humidity and feeding conditions. In spring the larvae infest the young shoots of numerous fruit trees, while in summer they feed on fruits. G. molesta attacks both wild and cultivated trees, but appears to prefer the latter.

The summer cocoons, covering the full-grown larvae and the pupae, may be found on fruit, in axils of twigs, and under pieces of bark.

The first signs of G. molesta infestation at the beginning of the growing season usually include clearly visible wilting, drying and brown lateral shoot tips (Il’ichev et al., 2003).

Damage by G. molesta on shoots and fruits can be similar to that of Anarsia lineatella.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control

Removing pruned material, as well as post-harvest fruits left on the tree and on the ground, can reduce the impact of G. molesta on orchards.

Chemical Control

Orchards can be protected against G. molesta by means of chemical control combined with cultural methods. Insecticide sprays can target newly hatched larvae, but applications are generally more effective if applied when G. molesata is capable of flight, preferably targeting the second and subsequent generations (Rice et al., 1996). The most appropriate time for insecticide application can be forecast by means of sex pheromone traps, which survey population levels and detect periods of flight. Early season insecticide treatments can reduce G. molesta populations in spring and can be followed by mating disruption applications for effective long-season control of G. molesta (Trimble et al., 2001; Kovanci et al., 2005).

Biological Control

There are numerous records of natural enemies of G. molesta, but none have been able to achieve control in the countries where G. molesta is an introduced pest.

In Australia, unsuccessful attempts were made to introduce natural enemies from the USA and Japan during 1935-1939 (Wilson, 1960) and a further unsuccessful attempt was made to introduce the braconid wasp Macrocentrus ancylivorus from the USA during 1977-1979 (Bailey, 1979).

In the USA, many different species were imported and released during the 1930s and 1940s. Although some species became established, they did not control G. molesta (Clausen, 1978). Introductions of M. ancylivorus were also attempted in Canada (McLeod, 1962), where G. molesta was already present; Argentina (Clausen, 1978); Brazil, Chile and Uruguay (Altieri et al., 1989); France and Italy (Greathead, 1976) and the former USSR (Izhevskii, 1988). Although M. ancylivorus became established in Argentina and the former USSR, no benefit resulted.

Investigations have been carried out on the use of biological control against G. molesta. Sprays of Bacillus thuringiensis have been found to have some effect against this pest.

Pheromonal Control

Pheromone-mediated mating disruption (MD) is now a major tool of long-term sustainable and area-wide integrated pest management (IPM) systems in horticulture. The release of large quantities of sex pheromone into a target crop can disrupt mate location and prevent or delay mating, thus reducing egg fertilisation and pest damage (Williams and Il’ichev, 2003).

Rothschild (1975) demonstrated that MD treatments could be as effective in controlling G. molesta as insecticides. Later research (Vickers et al., 1985) suggested that MD may become even more effective when all orchards in a district are treated, so as to reduce the likelihood of mated females migrating from untreated areas. In Australian orchards, hand-applied MD dispensers have been used successfully for long-term sustainable control of G. molesta for over 30 years. The initial approach was to treat individual orchard blocks and only known hosts with MD; however, an increase of G. molesta damage on the borders of MD treated blocks encouraged an area-wide application of MD for better crop protection (Il’ichev et al., 1999). An area-wide MD program, with more than 1,100 ha of 40 contiguous orchards covered with MD dispensers, applied to all fruit trees in northern Victoria, Australia, substantially improved protection against G. molesta damage (Il’ichev et al., 2002).

Long-term MD treatments have also been used successfully in many commercial orchards in Europe (Audemard et al., 1989; Zakharenko and Il’ichev, 2003; Witzgall and Arn, 1997), South Africa (Barnes and Blomefield, 1997) and America (Pree et al, 1994; Kovanci et al., 2004).

Although successful, an area-wide MD program to control G. molesta is expensive. To reduce the cost of an area-wide MD program, only infested blocks and border areas can be treated with MD (Il’ichev et al., 2004). Such a selective approach successfully controlled localised pest outbreaks and areas of increased infestation. Other trials investigated use of a reduced application rate of MD hand-applied dispensers (Il’ichev and Sexton, 2002), barrier MD treatments (Il’ichev et al., 2004) and new MD products, including sprayable microencapsulated sex pheromone formulations (Il’ichev et al., 2006), paraffin emulsion (Rice et al., 1997), wax-drop dispensers (Stelinski et al., 2005), aerosol puffers (Stelinski et al., 2007) and multispecies MD dispensers (Il’ichev et al., 2007). Sprayable microencapsulated pheromone products for MD have the advantage of easy application with standard spray equipment and compatibility with most insecticides and fungicides. Results of field trials demonstrated that fortnightly spray intervals provided G. molesta control equivalent to the performance of standard hand-applied MD dispensers and was more effective than monthly applications (Il’ichev et al., 2006). New multispecies hand-applied MD dispensers were also evaluated in seasonally replicated trials in Victoria, Australia, and Michigan, USA, over three years (Il’ichev and Williams, 2006).

Monitoring

Sex pheromone-based monitoring is the most effective survey method for detecting pest insects. It can be used for early detection and warning of pest invasion, taxonomic and biodiversity investigations, population density and dispersion trends estimation, forecasting and threshold determination, mapping of pest infested areas and risk assessment, recommendation of treatments and timing of application, measuring of treatment efficacy and impact on pest density (Sexton and Il’ichev, 2000).

Timing of chemical treatments can be determined by monitoring with sex pheromone traps and accumulation of degree-days (Rice et al., 1996). Different trap designs and sex pheromone lures were compared in field trials which suggested that sex pheromone traps could be used for monitoring seasonal abundance and determining biofix dates (male catches) for phenology models (Zalom, 1994).

Fermenting brown sugar, molasses, fruit juices and port wine have been used as bait traps to attract G. molesta males and females in fruit orchards, but were not species specific and also attracted many beneficial insects and pollinators (Yetter and Steiner, 1931). The addition of terpinyl acetate to fermenting brown sugar solution traps increased the attractiveness of bait traps to G. molesta males and, most importantly, mated females.

A comparison of sex pheromone and bait trap catches over a number of seasons in Australia demonstrated that they both recorded similar infestation figures and peak moth numbers (Rothschild et al., 1984). Sex pheromone traps designed to attract males in conventional orchards are not reliable under mating disruption. However, terpinyl acetate-fermenting brown sugar solution traps effectively attract G. molesta males and females in orchards under mating disruption treatment (Il’ichev et al., 1999; Il’ichev et al., 2002).

Recently, attempts had been made to combine both traps in one and use it for monitoring of G. molesta in disrupted orchards in Argentina and conventional orchards in Chile (Cichon et al., 2012). New host-plant attractants have recently been tested to improve pest monitoring, particularly for mated females of G. molesta in orchards treated with mating disruption (Il’ichev et al., 2009; Lu et al., 2012).

19/08/14 text updated by:

Alex Il'ichev, Department of Primary Industries Victoria, Australia