Posted on January 30, 2018
Leaf roller caterpillar a pesky pest of young Manuka
Observations indicate that Leaf roller caterpillars can cause significant damage to the fresh shoots of young manuka plants.
The Brown headed leaf roller moth, Ctenopseustis obliquana and Ctenopseustis herana (Lepidoptera: Tortricidae) is a native moth that is widespread throughout New Zealand, from coastal to subalpine regions.
The caterpillars feed on a wide range of hosts. They have been recorded on 48 genera of native plants in 36 families, including broad leafed and coniferous trees and ferns.
The caterpillars feed on the leaves, stem and buds of the plants, weaving webbed nests of silk and foliage. The apical buds on the leaders of young manuka plants are hollowed out and the stems chewed. Generally, a chewed plant will recover naturally, with fresh branching occurring from above the damaged parts of the plant. Larger plants are generally resilient to caterpillar damage.
In heavy infestations, the caterpillars may chew enough of the photosynthesising leaf mass of a young seedling plant, to weaken the plant enough to cause it to eventually die.
It would appear that dryer weather conditions during the warm summer months may create ideal breeding conditions for the moths. The caterpillar may also breed more rapidly if the plants are growing closer to other plant species that the caterpillars are attracted to, such as plantain species. Adult brown headed leafroller moths are about 12 mm in length with a wing span of up to 25 mm. Males are usually smaller than the females.
Fig. 1 – Adults of the brown headed leafroller Ctenopseustis obliquana. Male above: female below.
The line shows approximate wingspan.
Fig. 2 – Adult of the brownheaded leafroller Ctenopseustis obliquana..
The line shows natural length.
Colouration and markings on the forewing are variable, ranging from fawn to chocolate brown with darker markings.
The female moth lays flat masses of 30 or more eggs on the leaves of the host plant. When fully grown the ‘loopy’ caterpillars are about 10-15mm long and are green grey, translucent green and or pale yellow in colouring. The head and the next segment are shiny black. The ‘loopy’ caterpillar has three pairs of thoracic legs and five pairs of “prolegs” on the abdomen.
The caterpillars wriggle rapidly if disturbed, and drop suspended on a silken thread when dislodged from their protective webbing.
Fig. 3 – Ctenopseustis obliquana caterpillar.
The line shows natural length.
Pupation takes place inside the webbed nests with the fully-grown caterpillar spinning a tight silken cocoon about itself. The moth will breed almost all year round. In summer, the duration from egg to adult is 4-6 weeks. During spring and summer the caterpillars feed on foliage and growing shoots of the host plant with infestation observed when host plants are covered in small brownish nests of woven leaves and twigs. Where infestations are severe, the caterpillars will also chew flowers.
If severe levels of infestation are observed, it may be necessary to aerial spray a manuka plantation during the first summer after planting with a systemic insecticide such as Thiacloprid. Before applying any insecticide, it is necessary to take into consideration that the insecticide will also harm bees and most other insect species. It would not be advisable to spray any insecticide if beehives are nearby to a plantation.
In nature, populations of caterpillar are controlled by several insect predators. These include minute trichogrammatid wasps that feed on the leaf roller eggs, along with braconid, ichneumonid and eulophid wasps and tachinid flies that also feed on leaf roller larvae or pupae. A commonly found parasitoid species is the Australian leafroller parasitoid Dolichogenidea tasmanica. The predatory wasp Ancistroceros gazella paralyses leafroller larvae and stores them in its nest to provide food for its offspring.
Most research into natural predators of leafrollers in New Zealand has been conducted in orchards and vineyards where leaf rollers are a significant pest. There is little information available on what natural enemies are dominant in manuka or other plantation forests.