HortFACT
Identification
The adult, a grey, hard-bodied, pear-shaped weevil with a long, curved snout, is only 1.8>2.5 mm long. A covering of minute scales gives the weevil its grey colour, but if these scales are rubbed off the underlying colour is much darker.
The glistening yellow eggs are laid through a hole chewed by the female, singly or in clusters of up to 20 inside young green gorse pods.
Larvae are white, squat, legless grubs 2.0- 2.5 mm long with a very small, brown head.
Pupae are found inside the seed pod, and when newly formed are white. As the pupae develop their colour changes to grey.
The gender of adults can be determined by the relative length of the rostrum (snout). In males the rostrum length is approximately the same as the dorsal length of the thorax, whereas in females it is 1.5 times that length. Generally females are larger than males.
Host plant
This species feeds only on gorse. Dissection of adults has shown green gut contents in spring. Bronzing of foliage can be found during summer, and conspicuous holes in flowers are made by adults searching for oviposition sites.
Beneficial effects
The gorse seed weevil was released in New Zealand in 1931 with the aim of controlling the spread of gorse by reducing its seed crop. The adults may damage young shoots and flowers, but the significance of this damage and its effect on the plant is unknown. However, the larvae destroy up to 96% of the seed produced during spring and early summer.
In most of New Zealand, peak Apion Ulicis infestation of gorse pods occurs in spring. However, much of the seed is produced in autumn, and these seeds escape attack by the weevil. Its effectiveness as a control agent therefore appears to be limited. The effect of the weevil on gorse distribution and abundance in New Zealand is uncertain. Accurate assessment calls for further information about the amount of viable gorse seed already in the soil and the gorse plant's biology.
Distribution
Gorse seed weevil is a native of western areas of Europe and Great Britain. Between 1926 and 1932 321,000 weevils were imported from England to New Zealand. From 1931 approximately 240,000 weevils were released throughout New Zealand at 240 sites. The species established readily in all areas and is now extremely common. In coastal Westland, however, numbers are still low.
The adults disperse readily on warm winter days and throughout summer by flying from bush to bush. Populations are commonly found on isolated gorse plants, even in remote areas of New Zealand.
Life cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
Adults can be found on gorse bushes all year round in Canterbury. The life history varies from place to place depending on the climate. Peak adult populations occur from November to December in lowland Canterbury and from September to November in cooler areas.
Development from egg to adult takes approximately 16 weeks. The eggs take 4 weeks to hatch, the larvae take 6-8 weeks to pupate, and the pupae take 4 weeks to complete development within the pods. There is only one generation each year. In warmer climates weevils complete development between spring and early summer, but in cooler areas (e.g., at higher altitudes) development time is extended into midsummer. The eggs are found in green pods in early September to late October in Auckland and mid September to late November in Canterbury . Larvae are found in pods from October to January, and pupae from November to January, in both Canterbury and Auckland.
A tiny wasp-like ectoparasite (Pteromalus sp.) has been found attacking gorse seed weevil larvae in Canterbury, developing with them in the seedpod.
A. H. GOURLAY
Revised by R. HILL