FNZ 28 - Larvae of Curculionoidea (Insecta: Coleoptera) - Popular summary
May, BM 1993. Larvae of Curculionoidea (Insecta: Coleoptera): a systematic overview. Fauna of New Zealand 28, 226 pages.
( ISSN 0111-5383 (print), ; no. 28. ISBN 0-478-04505-0 (print) ). Published 14 Jun 1993
The weevils are one of the largest groups of Coleoptera, and in New Zealand about 1500 species are endemic. All weevils, or snout-beetles, feed on plant material, and are thus found in a wide range of habitats. Some live in the soil, feeding on roots; others live at soil level and feed on leaves or crowns. A group of mainly small species feed internally, boring into stems and mining between the upper and lower surfaces of leaves. Living trees may be attacked by bark beetles, and once a tree is dead many kinds of weevil enter to feed on the wood.
A very small proportion of species world-wide are pests of agriculture, forestry, commercial crops, and home gardens. Those that have been accidentally introduced into New Zealand have multiplied rapidly in the absence of population pressure and of their natural enemies.
Adult weevils, perhaps because of the relative ease with which many can be found, have always attracted the attention of collectors and are fairly well documented. Larvae, on the other hand, with their cryptic feeding habits and 'look-alike white grub' image, have largely been neglected. It is now realised that the character states in each larva are diagnostic, and can be used to determine its identity and relationships. For this purpose it is essential to have correctly identified specimens, and a reference collection of over 300 species has been amassed through an on-going programme of rearing. The search for larvae in their natural habitats, and subsequently their rearing through to the pupal and adult stages, have revealed details of their life history that were previously unknown. For instance, in the flower weevil group of about 100 very small native weevils each species was found to belong to its own particular host plant, where many larvae feed on the flowers and developing ovaries. Aneuma compta on lacebark waits until the seed capsules are fully expanded before inserting its single egg.
Some species are miners in green leaves. Most of them make individual burrows, but at least two species live communally, with up to 20 larvae in a single leaf. The minute adult of Geochus, with no wings and no claws on its feet, spends its whole life on the forest floor, where its larvae are miners in fallen leaves, feeding on the dead tissue.
Rhinorhynchus species are of particular interest in that they are the only representatives in New Zealand of the ancient family Nemonychidae. They develop on the male flowers of cone-bearing trees, where they feed on pollen; their mouthparts are modified for grinding pollen grains. About 3 weeks for larval growth is followed by a lengthy prepupal resting period in the soil, sometimes extending into a second season. This may be regarded as a strategy for survival, since at least some of the population will still be alive if the host tree fails to flower.
Wood-boring weevils of the genus Platypus are known as ambrosia beetles. They are gardeners, cultivating their food supply of fungus on the walls of their tunnels. The adult pair which start the colony bring in the first spores. Later, the garden is maintained and spread by the older progeny, which have mouthparts adapted for the purpose.