Apples and kiwifruit are the mainstay of New Zealand’s horticulture industry, but they can be damaged by a number of insect pests, making the fruit unsuitable for export. Some insects are known as quarantine pests because affected fruit is quarantined by countries receiving it.
Six species of leafroller are serious horticultural pests. Four are endemic and have adapted successfully to exotic fruit trees – they are the greenheaded leafrollers (Planotortrix octo and P. excessana) and the brownheaded leafrollers (Ctenopseustis obliquana and C. herana). The other two are the black-lyre leafroller (Cnephasia jactatana) and the light-brown apple moth (Epiphyas postvittana), originally from Australia. The apple moth also damages the leaves and fruit of berry plants and grapevines.
Leafroller moths are small, with a wingspan of 12–18 millimetres, and vary in colour from pale to dark brown. The larvae are green with a dark central stripe and two side stripes. Leafrollers are so called because they web together leaf edges or leaves and fruit to form a shelter to live in – often rolling the leaves into a tube. The caterpillars eat leaves and fruit. Leafroller damage is not tolerated on fruit for export.
Painted apples and Asian gypsies
Painted apple moths and Asian gypsy moths are not established in New Zealand, and strict biosecurity controls aim to keep them out. Either of these pests could do serious damage to private gardens and plantation forests. Parts of suburban Hamilton and Auckland were sprayed after single insects of these species were found.
Major pests of apples are caterpillars of the codling moth (Cydia pomonella), originally from Europe. Mature caterpillars are about 20 millimetres long, and pinkish-white with a brown head. Adult moths are a similar size to leafroller moths, but the forewings are grey and crossed with fine brown bands. Codling moth larvae scar the outside of fruit, but the damage caused by older larvae, which enter the fruit and feed on the core, is particularly severe.
Oriental fruit moth
Larvae of the oriental fruit moth (Grapholita molesta) damage stonefruit, in particular peaches, by penetrating the fruit.
Greedy scale (Hemiberlesia rapax), latania scale (H. latania) and oleander scale (Aspidiotus nerii) attack kiwifruit, while apples are affected by the San Jose scale (Quadraspidiotus perniciosis). Infestations are spread by the mobile, young scale nymphs or ‘crawlers’ – older nymphs and adults are sedentary.
To feed, scale insects insert a stylet into plants and suck the sap, producing sticky secretions which cause sooty mould and reduce plant vigour. Although damage is generally cosmetic, it is not tolerated on export fruit.
The species that affect horticultural crops are called armoured scale insects because of the protective shell covering older nymphs and adults. The shell makes them difficult to kill, but young crawlers are susceptible to insecticides, and older insects can be destroyed using mineral oil, either by itself or mixed with an insecticide. Encarsia citrina is an important parasite of armoured scale insects, and is used for biological control.
The apple leafcurling midge (Dasineura mali) was first recorded in New Zealand in 1950 and has since spread throughout New Zealand. Larvae of this small fly feed on developing shoots, causing severe stunting. This pest is parasitised by the wasp Platygaster demades, which was introduced to New Zealand in 1925 to control a related insect, the pear leafcurling midge (D. pyri).
Woolly apple aphid
The woolly apple aphid (Eriosoma lanigerum) infests the roots, leaves and branches of trees. It sucks plant sap, and heavy infestations prevent plants from growing and thriving. This aphid is parasitised by Aphelinus mali. Previously, organophosphate insecticides suppressed woolly apple aphid as well as apple leafcurling midges, but both pests have become more numerous with the introduction of an integrated pest-management system of fruit production, which relies less on chemical sprays.