Oreocalus albosparsus (Broun, 1913)
Hebe leaf & stem borer
Oreocharis albosparsus Broun, 1913
Biostatus and distribution
This endemic weevil lives in its Hebe shrub host plant, Veronica macrocarpa (Plantaginaceae). The weevil has been found in West Auckland, though it may live elsewhere on its host plant which is found in coastal and upland areas from the Waitato Northwards.
Conservation status: Unknown, but unlikely to be threatened.
Life stages and annual cycle
The Adults are typical weevils, each has six legs, hard wing covers (elytra) and a long snout (rostrum). They are about 5 mm long and dark brown. Their wings, which are longer than the wing covers, are kept safely folded up under the elytra, except when needed for flying. The two jaws, or mandibles, are at the end of the rostrum and on either side of the mouth. The antennae are also attached near the tip of the rostrum.
Eggs and larvae
Female weevils lay eggs singly by the mid rib of young leaves. After hatching from its egg the larva burrows into the mid rib of the leaf and tunnels down it and through the short leaf stalk into the stem. It first tunnels up the young stem, then turns round and burrows down into the woody stem tissue. Larvae are pale brown, with no legs and a brown head capsule that has a strong V-shaped invagination on the upper (dorsal) side. Larvae have large jaws at the front of the head. As a larva grows, it changes skins (moults). It is not known how many larval stages (instars) this weevil has. Eggs are laid in the young leaves in summer. Larvae reach full size by late winter.
When it is fully grown, the larva creates a pupation chamber within the stem of its host plant. The two ends are packed with the waste wood from the larva’s chewing out the chamber. Near the head of the pupa the wood has been chewed away leaving a window of epidermis covering the opening though which the adult escapes. The pupa is white with all the appendages of the adult weevil visible - long legs, rostrum (snout), wings and wing cases. In spring, on emergence from the pupal skin, the adult weevil stays in the pupal chamber until its skin (cuticle) hardens and darkens. The adult leaves through the thinly covered hole made by the larva. After leaving the pupal chamber the males and females find one another and mate. The female probably feeds on the plant before laying eggs in suitable young leaves.
Both adult and larval weevils have chewing mouth parts.
The mandibles of the adult are at the tip of the rostrum. When the adult wants to feed, the rostrum is pushed onto the leaf surface and the mandibles bite the leaf tissue.
The larva also has mandibles (jaws) at the front of its head. It uses them to create a tunnel in the midrib of the leaf and in the plant stem. The digested leaf tissue and stem is excreted as discrete pellets (frass) that back-fill the mine or tunnel.
There are many kinds of small weevils in New Zealand. They can only be distinguished by an expert. At least nine species of the genus Oreocalus have larvae that burrow into stems of Hebe, shrubby Veronica species. The Hebe leaf & stem borer, Oreocalus albosparsus is the only species that burrows into live stems of Veronica macrocarpa (Plantaginaceae), though other weevils burrow in its dead stems.
The presence of the larvae in a plant can be recognized by the distinct mine in the mid rib of leaves. The presence of wilted shoots is a signal to look for the mid rib mine.
Larvae of several leaf mining flies. Liriomyza species (Agromyzidae), form mines in the leaf lamina and are very different from the weevil mines that are restricted to the mid rib.
No pathogens or predators of the Leaf and stem borer weevil are known. Adult weevils are probably preyed on by birds and spiders.
Two species of parasitoid wasp have been reared from this weevil. One belonging to an unidentified genus in the family Proctotrupidae (Hymenoptera) was reared from larvae and pupae of this weevil by Brenda May who studied weevil larvae.
The second species of unknown family, was reared while collecting material for this factsheet. The female probably lays an egg in the young weevil larva while it is in the leaf mine or burrowing in the young plant stem. After hatching from its egg, the wasp larva feeds in the weevil larva, but does not kill it. When the weevil larva is fully grown or has pupated, the fully grown wasp larva kills its host in its pupation chamber. The wasp larva leaves the weevil and pupates in its burrow. When the wasp adult is ready, it emerges from the pupal skin and its body and wings harden. It probably emerges from the weevil pupal chamber through the exit, a weak area in the plant stem wall, prepared by the weevil. The dark coloured adults have two pairs of wings. The female has a long pointed abdomen that contains an ovipositor for inserting eggs into the weevil larvae in their burrows.
The Hebe leaf & stem borer weevil lives in its Hebe shrub host plant, Veronica macrocarpa (Plantaginaceae). The weevil has been found in West Auckland. It probably lives elsewhere on its host plant which is found in coastal and upland areas from the Waikato Northwards.
The weevil larva burrows through the mid rib of a young leaf into the young stem of the plant. It first burrows upwards in the young stem. It then burrows downwards into the older thicker stem in which it pupates. It is likely that the adult weevils also feed on young leaves. They probably make holes in the leaf with their rostrum (snout).
May BM. 1987. Immature stages of Curculionoidea (Coleoptera): rearing records 1964-1986. New Zealand Entomologist. 9: 44-56.
Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.