Larvae of the light brown apple moth eat pretty much anything — this is never a good sign in a pest. By Anna Mouton.
The light brown apple moth — Epiphyas postvittana — is a leaf-roller moth in the well-known Tortricidae family. Its big-name relatives include codling moth, false codling moth, Oriental fruit moth, and pear leaf roller.
Why does light brown apple moth matter?
The larvae of the light brown apple moth have a seemingly limitless host range. They are known to feed on at least 545 plant species in 121 families. Commonly recorded hosts include all major pome and stone fruits, grapevines, olives, lemons, and many ornamental plants. Plants in the erica and protea families have also been noted as hosts.
Many common orchard weeds make excellent fodder for overwintering larvae. Favourites include white clover, ribwort plantain, white goosefoot, red amaranth, and our very own Cape weed — botterblom or gousblom in Afrikaans. Laboratory studies have found that larvae survive better on herbaceous than woody plants.
Young larvae of light brown apple moths spin shelters on the surface of leaves. Older larvae make feeding niches by attaching leaves to each other or to fruit. They also fold leaves to construct the leaf rolls for which leaf-roller moths are named. Larvae feed on the surfaces of leaves and fruits. Some larvae enter fruit through the calyx and cause internal damage.
The economic impact of Epiphyas postvittana is partly due to direct damage and partly due to control costs. Fruit damage of 5–20% has been reported from its native Australia when pesticides were not used — the figure for New Zealand is commonly 50%. The 2008 United States Department of Agriculture budget for eradication, monitoring, research, and regulation of light brown apple moth was USD 74.5 million.
Epiphyas postvittana does not occur in South Africa. If it were to establish here, there is a good chance that it would threaten not only commercial fruit production but also native plants. There would be significant phytosanitary implications for any affected host.
How do I recognise this moth?
Leaf-roller moth larvae tend to all look the same. They start out nearly translucent and become darker with age. Mature larvae are green and have a darker central stripe and two side stripes.
Adult light brown apple moths are neither noticeable nor distinctive. The front wing is 6–10 millimetres long in males — in the same ballpark as codling moths — and 7–13 millimetres in females. They are light brown to pale yellow but the part of the wing that is further from the body is often darker brown. Some individuals have patterned wings.
Entomologists consider examination of the male genitalia essential for the identification of light brown apple moths — something probably best left to the experts. Larval identification requires DNA testing.
How do these moths make more moths?
Female light brown apple moths lay eggs in groups of around 30 on the upper surfaces of leaves. A single female will lay anything from a few dozen to as many as 1 500 eggs. The total depends on factors such as larval diet and weather. Ribwort plantain and curly dock seem to be winner hosts for these moths.
Eggs hatch after 1–2 weeks. Larvae disperse by crawling or ballooning — spinning a silk thread that acts as a parasail. They then settle down to eat, moult, repeat, eventually growing to 1–2 centimetres in length. Larvae usually pupate in the shelters they constructed.
The rate of development of different stages of Epiphyas postvittana is determined by temperature. They do best at 20–25 °C but can develop at 7–31 °C. There is no winter dormancy. The light brown apple moth has 2–4 generations per year depending on the climate.
Adult moths obviously fly — males can travel at least 600 metres and females at least 300 metres. But the global spread of this pest was only possible due to human activities.
Where did it come from?
Epiphyas postvittana is an Australian native that occurs throughout the southwestern parts of the continent. It was possibly introduced into New Zealand more than once where it has become one of the most common small moths in cultivated and disturbed land.
The light brown apple moth was first recorded in the United Kingdom in 1936. It has spread rapidly throughout much of England and Wales in the last few decades. The moths have also been reported from Ireland, Portugal, and Sweden. It is believed that Epiphyas postvittana travelled to New Zealand and the United Kingdom with plant material, and spread within the United Kingdom with nursery stock.
In the United States, the light brown apple moth has been present in Hawaii for more than a century. It was first detected in California in 2005. Subsequent trapping found widespread populations in the state. Eradication efforts devolved into the so-called light brown apple moth controversy following a public outcry after the aerial spraying of pheromones in 2007.
The light brown apple moth has not been found in South Africa, South America, or Asia.
Control of light brown apple moth
Control measures for light brown apple moths are similar to those for related pests like false codling moths.
Pesticide sprays are used in Australia and New Zealand. Light brown apple moth was reported to be adequately controlled by a codling-moth spray programme in certain areas of Australia. Pheromone trap thresholds can be used to guide pesticide applications.
The bacterium Bacillus thuringiensis kurstaki is used to control the moths on vineyards in Australia. Use on apples appears to be less effective due to more rapid degradation in open canopies.
Effective mating disruption is available for Epiphyas postvittana.
Several parasitoids and predators attack Epiphyas postvittana in its home country. Some have been introduced to New Zealand as biocontrol agents. Their success appears to depend on the host plants used by the moths, as well as on the extent and type of pesticide applications.