INTERESTING INSECTS

By N A Martin (2017, revised 2018)

Pittosporum flower weevil

Erirhinus rubricalis Broun, 1880

Erirhinus creperus Broun, 1881

Erirhinus simulans Broun, 1881

Erirhinus stramineipes Broun, 1886

Aneuma stramineipes (Broun, 1886)

Aneuma ferrugineum Broun, 1886

This endemic weevil lives in the North and South Islands of New Zealand where its host plants, species of Pittosporum, occur. The weevil lives in city gardens and parks as well as in native ecosystems. Larvae live in flowers, while adults feed on young leaves.

Conservation status: Widespread, not threatened.

In spring, adult female weevils lay eggs in flowers of its only known larval host plant, Pittosporum tenuifolium (Pittosporaceae). Larvae feed in the flowers and mature larvae drop to the ground and pupate in chambers made in the soil. Adults emerge in late spring/early summer and feed on young leaves of several Pittosporum species. It is likely that after feeding, they hide until spring.

Adults are typical weevils, each with six legs, hard wing covers (elytra) and a long snout (rostrum). They are small, about 2.5 mm long and brown. Their wings, which are longer than the wing covers, are kept safely folded up under the wing covers, 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. After adults emerge from the pupal chambers in the soil, they locate suitable food plants. They feed at night and hide during the day. They drop to the ground if disturbed. It is not known if they mate at this time or wait until spring.

Eggs and larvae

Female weevils lay eggs flowers in the spring. A single egg is laid in a flower or a bud that is about to open. After hatching from an egg, the larva feeds on tissue in the flower, including the anthers and the ovaries. A larva feeds in several flowers. Larvae are whitish, with no legs and a brown head capsule. Larvae have jaws at the front of the head. As a larva grows, it changes skin (moults). It is not known how many larval stages (instars) this weevil has. Larval development usually takes several days.

Pupa

When it is fully grown, the larva 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. The adults then find young leaves on which to feed.

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 holes 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 tiny ‘window’. When a young leaf expands, the hole enlarges. A beetle makes many small holes in each nights feeding session. When the beetle feeds on very young leaves its claws make tiny marks around the feeding hole.

The larva also has mandibles (jaws) at the front of its head which it uses to feed on the internal structures of flowers. The digested flower tissue is excreted as discrete pellets (frass) that can be seen in flowers.

Adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), top view. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA9]

Underside of an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), underside. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA5]

Side view of an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), side view. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA7]

Underside of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with fresh holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAD]

Upper side of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with windows over fresh holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAC]

Underside of a lemonwood, Pittosporum eugenioides (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae), note the dark colour of the plant reaction around each hole. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAB]

Top side of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAA]

Underside of a, Pittosporum tenuifolium (Pittosporaceae) leaf with the feeding hole and the claw marks made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), note the dark colour of the plant reaction around each damage site. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAF]

Mature larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAR]

Mature larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAS]

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae) feeding in a flower; arrow points to larva. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAM]

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae) feeding in a flower; arrow points to larva. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAN]

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show feeding damage by larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAL]

Pupa of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae) in chamber made in soil, note the moulted larval skin with head capsule and mandibles. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAT]

Pupa of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), note the moulted larval skin with head capsule and mandibles. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAU]

Pupa of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAV]

There are many kinds of small weevils in New Zealand. They can only be distinguished by an expert. However, tiny weevils on leaves of certain Pittosporum species at night and making many tiny holes in young leaves are likely to be the pittosporum flower weevil, Aneuma rubricale (Broun, 1880). The presence of the weevil can be recognised by the tiny holes in leaves of host plants, Pittosporum eugenioides, P. tenuifolium. Similar holes in leaves of Pittosporum colensoi and P. umbellatum are also likely to be made by the pittosporum flower weevil.

Weevil larvae in flowers of Pittosporum tenuifolium are also likely to be the pittosporum flower weevil. Weevil larvae in flower buds Pittosporum tenuifolium are likely to be another species of weevil, Aneuma fulvipes Pasco, 1876.

Adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), about 2.5 mm long. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA6]

Adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), top view. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA9]

Top side of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAA]

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae) feeding in a flower; arrow points to larva. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAN]

No natural enemies of the pittosporum flower weevil have been reported. Adult weevils are probably preyed on by birds and spiders and larvae may be preyed upon by insect predators.

The larvae of the pittosporum flower weevil has only been found in living in flowers of Pittosporum tenuifolium Sol. ex Gaertn. (Pittosporaceae). The adult beetles have been found feeding on two species of tree, Pittosporum eugenioides A. Cunn. and P. tenuifolium, while similar leaf damage has been found on two other species, Pittosporum umbellatum and Pittosporum colensoi.

Plant damage

The weevil larvae feed on the stamens and ovaries of the flowers and a single larva feeds in several flowers. Damage to the ovary and presence of black frass are signs of weevil feeding.

Adult weevil feeding on young leaves results in more prominent damage. Adult weevils mainly feed on the underside of leaves. In a single night they make numerous small holes in a leaf, but do not break through the upper epidermis (skin) of the leaf. After a few days the plant reacts to the damage by surrounding the hole with dark coloured tissue. If a weevil feeds on a very young, soft leaf, its claws puncture the leaf and dark tissue also surrounds these claw marks.

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show feeding damage by larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAL]

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae) feeding in a flower; arrow points to larva. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAP]

Flower of black matipo, Pittosporum tenuifolium (Pittosporaceae), dissected to show larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae) feeding in a flower; arrow points to larva. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAQ]

Mature larva of pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAS]

Underside of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with fresh holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAD]

Upper side of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with windows over fresh holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAC]

Underside of a lemonwood, Pittosporum eugenioides (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae), note the dark colour of the plant reaction around each hole. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAB]

Top side of young leaf of lemonwood, Pittosporum eugenioides (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAA]

Underside of a, Pittosporum tenuifolium (Pittosporaceae) leaf with the feeding hole and the claw marks made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), note the dark colour of the plant reaction around each damage site. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAF]

Underside of a Pittosporum tenuifolium (Pittosporaceae) leaf with the feeding hole and the claw marks made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), note the dark colour of the plant reaction around each damage site. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAG]

Side view of an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), side view. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA7]

Underside of an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae), underside. Creator: Tim Holmes. © Plant & Food Research. [Image: 2IA5]

Underside of a lemonwood, Pittosporum tenuifolium (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAI]

Upper side of a lemonwood, Pittosporum tenuifolium (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAJ]

Underside of a lemonwood, Pittosporum tenuifolium (Pittosporaceae), leaf with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAK]

Underside of a lemonwood, Pittosporum tenuifolium (Pittosporaceae), leaf with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2IAH]

Underside (left) and upper side (right) of Pittosporum umbellatum (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2IA3]

Underside (left) and upper side (right) of Pittosporum umbellatum (Pittosporaceae), with holes made by adult pittosporum flower weevils, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2IA4]

Upper side of a Rautāwhiri, Pittosporum colensoi (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2IAX]

Upper side of leaves of Pittosporum cornifolium (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2SB9]

Upper side of a young leaf of Perching kohukohu, Pittosporum fairchildii (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae): note the claw marks around each feeding hole. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2SBA]

Upper side of a leaf of Perching kohukohu, Pittosporum fairchildii (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2SBB]

Underside of a leaf of Perching kohukohu, Pittosporum fairchildii (Pittosporaceae), with the feeding holes made by an adult pittosporum flower weevil, Aneuma rubricale (Coleoptera: Curculionidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2SBC]

Using flower weevil leaf holes

In Canterbury, a tiny felted scale, Eriococcus aconeae Henderson, 2006 (Hemiptera: Eriococcidae), lives in the holes in leaves of Pittosporum eugenioides made by adult pittosporum flower weevil feeding. The mature scale is covered with a small tent of brownish felted material.

Martin N. 2010. Host plants of some adult weevils (Coleoptera: Curculionidae). The Weta 39: 29-36.

May BM. 1987. Immature stages of Curculionoidea (Coleoptera): rearing records 1964-1986. New Zealand Entomologist. 9: 44-56.

May BM. 1993. Larvae of Curculionoidea (Insecta: Coleoptera): a systematic overview. Fauna of New Zealand. 28: 1-223.

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

1 August 2018. NA Martin. Host plant list updated, photos of leaf damage added.