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Oriental fruit moth | AG0156 |
David Wiliams, Knoxfield
June 2000 |  |
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The oriental fruit moth (Cydia molesta Busck) has been a serious pest in canning peach orchards of the Goulburn Valley since the early 1930s, and now also infests Nashi and some other pome fruit. The larva or caterpillar of the moth bores into the tip growth of quinces, peaches, nectarines, apricots, plums, and, occasionally, into some other fruits such as apples and pears. Later generations bore into the fruit as well.
Economic importance
In the 1930s, untreated peach orchards lost as much as 80% of the crop to the larvae of oriental fruit moths. Unless control measures are undertaken in peach orchards in the Goulburn Valley and Cobram districts today, similar losses may result and the spread of the disease brown rot will be enhanced. In peach orchards in these districts the pest control program revolves around the control of oriental fruit moth because this is the key pest. Late-maturing varieties of peaches always suffer greater losses than early varieties, even under good spray programs. Other fruit crops attacked by oriental fruit moth generally suffer only light damage, and control measures are rarely needed. However, oriental fruit moth populations in such crops can cause problems for peaches and nashi, grown in neighbouring blocks, by migrating into these crops.
Life history and habits
Creamy-white overwintering mature larvae emerge from the fruit in late summer and autumn, and wander in search of suitable hiding-places for the winter. When they have chosen their overwintering sites they immediately spin their silken cocoons. Most cocoons are spun under bark near the base of the host tree, in wounds from broken limbs or in litter on the ground. The cocoons are about 15 mm long by 3 mm wide at the centre.
The dormant larval state remains until late winter or early spring, when transformation into the pupal state occurs. The pupae are about 6 mm long and are at first yellowish, but quickly turn brown and then almost black, just before the moth emerges. This may be at any time from August to early November, depending on the temperature.
The moths are about 7 mm long; the males are slightly smaller than the females. Both sexes have similar markings but, unlike the codling moth, are rather dull in appearance, being basically grey with small light grey areas on the back.
Moths are inactive during the day and are rarely seen, but during the late afternoon on warm days they can be seen in flight near the tree tops. Light and temperature both play an important role throughout the insect's life cycle, beginning with moth mating and finishing with moth emergence.
The growth of an insect increases as temperature increases until the optimum temperature for the particular insect is exceeded, at which point the growth rate rapidly declines. There is also a lower developmental threshold which is the temperature below which no measurable growth occurs. The lower developmental threshold for oriental fruit moth is 7.5°C.
Insect growth is measured in physiological time units called degree-days. A degree-day is essentially each degree of temperature by which the average temperature on a day exceeds the lower developmental threshold. For oriental fruit moth a rough approximation can be obtained from the formula:
The moths are only active in dim light when the temperature is high enough, probably above 18°C. If these conditions prevail, mating, followed by egg laying, will occur. The eggs which are small round scale-like objects, are cream in colour and less than 1 mm in diameter. During the spring the whole life cycle of the insect is slow because of low temperatures, and the period over which eggs are laid may be up to 18 days, with 125 to 150 eggs being deposited on twigs and leaves. Just before hatching, the black head of the young larvae can be seen through the egg shell. Egg hatching takes 110 degree-days (from 10 to 14 days when the night temperatures are low, and averages 10 days during the spring in the Goulburn Valley).
The newly-hatched larvae, which are 1.5 mm long and white with a black head, burrow into the growing tips of the trees and feed for up to four weeks during the spring. The young shoots soon wilt and collapse, producing gum as they die. The mature larva, which is now pinkish with a brown head, and about 12 mm long, searches for a suitable cocooning site, usually high in the tree near where it has been feeding.
The larva spins a cocoon, which is weaker than those spun by overwintering larvae, and pupates immediately, to emerge as an adult, between the middle of November and early January. The total period for the completion of the first generation averages 555 degree-days (about 50-70 days). Subsequent generations take the same number of degree-days but since temperatures are generally warmer it takes less days to accumulate 555 degree-days (about 28-44 days).
A small proportion of the larvae of the second generation attacks green peaches, causing them to exude gum. Generally damage to green fruit will be slight, but it could be excessive if the trees have poor tip growth or are attacked by very large numbers of oriental fruit moths .
When tree growth ceases and the shoots begin to harden, usually in January, fruit damage becomes more significant, with maximum damage occurring just before harvest.
When ripening fruit is attacked the damage is often only observed when the fruit is cut. Ninety per cent of the entries are made at the point where two peaches, or a peach and a leaf or a peach and a branch, are in contact. The newly-entered larva soon burrows to the stone, filling the tunnel with brown particles of excreta. But unlike the damage caused by codling moth in apples and pears, this excreta is not usually conspicuous on the outside of the peach. Hence, much damage goes unnoticed on the grader. The damage to plum fruit is often more obvious and that done to apples, pears and nashi is superficially identical to that caused by codling moth.
Four to six generations of oriental fruit moth occur each year in the Goulburn Valley, with varying proportions of the last three generations entering the overwintering state to give rise to the emergence of adults in the following spring .
Control measures
The need for spray applications should be determined according to lure pot or pheromone trap catches. Sprays can be timed by reference to predictive models. In the past up to five or six insecticide sprays were used to reduce oriental fruit moth damage to peaches, especially for late-maturing varieties. These sprays induced the build-up of pests such as the two-spotted mite and the light brown apple moth, which were normally kept largely under biological control by predators and parasites.
The predatory mite, Typhlodromus occidentalis, which is resistant to many pesticides was introduced into Victorian orchards in 1976 to control twospotted mite. However, there are some insecticides and fungicides that have a toxic effect on this predator, and should not be used in orchards where it is established.
The use of mating disruption for control of oriental fruit moth has been successful in areas with a low population of oriental fruit moth. The technique works best over large areas and where alternative hosts are not present. Mating disruption can be augmented with pesticides if the population is high. Alternative hosts such as pome fruit should be treated with mating disruption to prevent migration of mated female moths.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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