T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Weevil (Longnosed kauri weevil) Mitrastethus baridioides

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Suborder: Polyphaga
Infraorder: Cucujiformia
Family: Curculionidae
Genus: Mitrastethus
Species: M. baridioides
Scientific name: Mitrastethus baridioides
Synonyms: Mitrastethus brouni
Common name: Longnosed kauri weevil

Mitrastethus baridioides (Longnosed kauri weevil) is a native weevil found throughout most of New Zealand. It larva infests dead moist or wet wood of many tree species. 

The first recording of this insect was of it attacking dead Agathis australis (Kauri), hence its common name. Other hosts are conifers species, Cupressus species, Dacrydium cupressinum (Rimu), Juniperus chinensis (Chinese Juniper), Pseudotsuga menziesii (Douglas fir), Sequoia sempervirens (California redwood), Acacia, Eucalyptus and Pittosporum species.
These insects are often found infesting stockpiled logs especially in the wetter parts of forests. Untreated milled and stacked Pinus radiata are attacked but this is invariably associated with damp, poorly ventilated conditions. Infected pine logs destined for export has necessitated fumigation to conform with New Zealand export regulations.

The adults, which are abundant between January and April, may be found in large numbers in localised areas beneath the bark of logs and stumps, and under logs. A period of aggregation occurs, probably associated with mating. On one occasion 300 to 500 beetles per stump were recorded. Campers have reported having 100s of the flying adults attracted to their lights.
The newly emerged adults are a pale yellow to brown or grey because of the numerous scales covering it. These are of two types of scales: short and rounded which lie flat covering the whole body and legs, and elongated scales which are more upright dotted at regular intervals along the elytra (wing cases) and legs. These scales readily become rubbed off exposing the dark red elytra.
The snout, which curves downward, is about as long as the prothorax (the foremost of the three segments in the thorax of an insect, and bears the first pair of legs) and bears a pair of distinctly elbowed antennae attached near its mid-point. The prothorax is finely punctured and constricted in front, widening out to the elytra. The elytra are wider than the prothorax and nearly parallel for about three-quarters of their length, then become rounded. There is a rounded protruberance on the rear slope of each elytron (a modified, hardened forewing). Regular rows of punctures are evident on abraded specimens. The insect is 6 to 9 mm long and 2 to 3 mm wide.

During summer the eggs are usually laid singly in small pits cut in the bark by the female, or beneath the bark at the edges of damaged areas where the sapwood has been exposed. Attack is confined to very moist wood which appears essential to successful larval development. The larva is a small, white, C-shaped grub with no legs and a yellowish brown head capsule. The larvae honeycomb the sapwood with a network of tunnels, often working backward and forward enlarging certain sections. Larval development probably takes from 1 to 3 years.

Thanks to New Zealand Farm Forestry Association http://www.nzffa.org.nz/ for the above information  

This is a young adult whose body had not yet as abraded. The pale squamosity rubs off very easily.
An older beetle is totally brown.