INTERESTING INSECTS

By N A Martin (2018)

Totara leafminer weevil

Erirhinus flavitarsis Broun, 1880

Dorytomodes flavitarsis (Broun, 1880)

This endemic weevil lives in the North and South Islands of New Zealand where its main host plant Totara, Podocarpus totara (Podocarpaceae) occur. It also lives on other Podocarpus species though it has not been reared from them. The weevil lives on host plants in city gardens and parks as well as in native ecosystems. The adults chew young leaves, while the larvae tunnel in leaves.

Conservation status: Widespread, not threatened.

Adults are typical weevils, each has six legs, hard wing covers (elytra) and a long snout (rostrum). They are small, about 3 mm long and brown with a distinctive orange rear end. Their wings, which are longer than the wing covers, are kept safely folded up under the elytra, except when needed for flying. A pair of jaws, or mandibles, is at the end of the rostrum and on either side of the mouth. The antennae are also attached near the tip of the rostrum. The adults are brown with orange at the end of the elytra.

Eggs and larvae

Female weevils start laying eggs when new leaves appear. A single egg is inserted into the blade of a young leaf. After hatching from an egg the larva tunnels into the leaf forming a mine that goes on either side of the midrib. After eating most of the leaf, the larva makes a round exit hole in the skin on the underside of the leaf and enters another young leaf on its underside. On its way in the larva excretes the digested remains of the leaf outside the leaf.

Larvae are yellowish, 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. Larval development usually takes about several weeks.

Pupa

When it is fully grown, the larva cuts a round hole in the skin (epidermis) on the underside of the leaf, crawls out and drops to the ground. It burrows into the litter or soil and makes a chamber in which it pupates. The pupa is white with all the appendages of the adult weevil visible - long legs, rostrum (snout), wings and wing cases. If the chamber is opened, the pupa waves its abdomen about. On emergence from the pupal skin, the adult weevil stays in the pupal chamber until its skin (cuticle) hardens and darkens. After leaving the pupal chamber the males and females find one another and mate. If suitable young plant foliage is available, they feed and lay eggs, even in autumn. However, most emerging adults wait until spring and the new flush of foliage, before laying eggs. Adults feed at night and hide during the day. They drop to the ground if disturbed.

Feeding

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, making a small round or oval hole in the leaf. The weevil does not eat right through the leaf, but leaves the skin (epidermis) on the far side of the leaf intact, so creating a ‘window’. The rostrum is pushed into the leaf and eats the tissue around the hole.

The larva also has mandibles (jaws) at the front of its head. It uses them to create a tunnel in the leaf. It ingests the internal tissue of the leaf and leaves the upper and lower skins of the leaf intact. Weevil larvae feed in leaves while they are attached to the plant. The digested leaf tissue is excreted as discrete pellets (frass) that back-fill the mine or outside the leaf when it is making a new mine.

Adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) on a shoot of Totara, Podocarpus totara (Podocarpaceae): note the long rostrum with antennae near the end and the orange end of the elytra (wing covers). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXP]

Top of an adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae): note the long rostrum with antennae near the end and the orange end of the elytra (wing covers). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXR]

Two images of the top of an adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae): note the long rostrum with antennae near the end and the orange end of the elytra (wing covers). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXS]

Two images of the underside of an adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae): note the long rostrum with antennae near the end. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXT]

Adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) on a shoot of Totara, Podocarpus totara (Podocarpaceae): note the long rostrum with antennae near the end. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXN]

Underside of young leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXL]

Upper side of young leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXM]

An egg of a Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) laid on a leaf of Totara, Podocarpus totara (Podocarpaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RY1]

An egg of a Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) laid on a leaf of Totara, Podocarpus totara (Podocarpaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RY2]

Underside of young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the exit and entry holes made by the larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RX7]

Upper side of young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RX8]

Two images of the upper side of a larva Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RX9]

Three images of the underside of a larva Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXA]

A pupa of Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) in a cell made in the soil by the mature larva. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXB]

Three pupae of Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) in cells made in the soil by mature larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXC]

Three images of a pupa of Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXD]

A newly emerged adult of Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) with its pupal skin in a cell in the soil. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXF]

A newly emerged adult of Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) in a cell in the soil. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXE]

There are many kinds of small weevils in New Zealand. They can only be distinguished by an expert. However, those found on the young foliage of the different species of Totara are likely to be the Totara leafminer weevil. The reddish-orange colour of the ends of the elytra (wing covers) is also characteristic of the species.

The presence of the adults can be recognised by their distinctive feeding damage to young leaves that can also be seen in mature leaves.

The presence of larvae can be recognised by the mines they make in the young leaves. Some of these can be seen in mature leaves. There is a caterpillar Chrysorthenches polita (Philpott, 1918 (Yponomeutoidea, Lepidoptera) that makes mines in Totara leaves, but the appearance of these mines has not been reported.

Adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae): note the long rostrum with antennae near the end and the orange end of the elytra (wing covers). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXQ]

Adult Totara leafminer weevil, Peristoreus flavitarsis (Curculionidae) on a shoot of Totara, Podocarpus totara (Podocarpaceae): note the long rostrum with antennae near the end and the orange end of the elytra (wing covers). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXP]

Mature leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made in young leaves by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXG]

Underside of mature leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made in young leaves by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXH]

Underside of young leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXI]

Underside of mature leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made in young leaves by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXK]

Upper side of mature leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made in young leaves by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXJ]

Underside of mature leaves of Totara, Podocarpus totara (Podocarpaceae) with mines made in young leaves by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the exit and entry holes made by the larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXU]

Young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXV]

Young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXW]

Adult weevils are probably preyed on by birds and spiders, but no observations of predation have been reported. No natural enemies of the larvae have been reported.

The Totara leafminer weevil has been reared from Totara, Podocarpus totara, and similar leaf damage has been found on two other Podocarpus species incudng the distinctive larval damage to young leaves in Hall’s Totara.

Plant damage

The weevil causes two kinds of damage to young Totara leaves. The larvae tunnel through a leaf, feeding on most of the tissue between surface layers, epidermis, of the leaf. The larva makes an exit hole and then burrows into another leaf. Each larva makes mines in several leaves.

Adult weevils also feed on the leaves. They make round or oval holes in the leaf with their rostrum (snout). In late summer when there are few shoots with young leaves, the shoots can be badly damaged.

Mature leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made in young leaves by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXG]

Underside of mature leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made in young leaves by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXH]

Underside of young leaves of Totara, Podocarpus totara (Podocarpaceae) with feeding damage made by adult Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the hole made by the end of the rostrum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXL]

Underside of mature leaves of Totara, Podocarpus totara (Podocarpaceae) with mines made in young leaves by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the exit and entry holes made by the larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXU]

Underside of young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae): note the exit and entry holes made by the larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RX7]

Upper side of young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RX8]

Young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXV]

Young leaves of Totara, Podocarpus totara (Podocarpaceae) with mines in leaves made by larval Totara leafminer weevils, Peristoreus flavitarsis (Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2RXW]

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.