INTERESTING INSECTS

By N A Martin (2017)

Coprosma flea beetle

Phyllotreta rugulosa Broun, 1880

Trachytetra frontalis Broun, 1923

This small endemic flea beetle is found in both the North and South Islands where its host plants, Coprosma species (Rubiaceae), grow. Adult beetles feed on young leaves in winter and spring.

Conservation status: Widespread in native ecosystems, common in the Auckland region.

Adults are found feeding on young leaves in winter and spring. It is presumed that eggs are laid in the soil and that larvae feed on plant roots and pupate in the winter.

Adults are typical beetles, each with six legs and hard wing covers (elytra). These beetles are about 2.5 mm long. The dorsal (upper) side of the thorax (middle body section) and the elytra are medium brown. The elytra have darker areas. These dorsal areas are covered in punctures. Their wings, which are longer than the wing covers, are kept safely folded up under the wing covers, except when needed for flying. The last pair of legs have enlarged femurs that enable the beetle to jump, hence the name flea beetle. This species is wingless (Kuschell 1990).

Nothing is known about the eggs, larvae or pupae of this beetle.

Feeding

Adults have chewing mouth parts. They feed on young leaves of Coprosma species. Adult beetles chew small holes in leaves. On thicker leaves they mainly chew from the underside, but do not eat right through the leaf, leaving the skin (epidermis) on the far side of the leaf intact, so creating a 'window'. Beetles probably feed mainly at night but can be found feeding on leaves during the day.

Adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETJ]

Underside of adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETH]

Adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETI]

Adult Coprosma flea beetles, Trachytetra rugulosa (Coleoptera: Chrysomelidae) mating. Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETN]

Adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae) feeding on leaf of Glossy karamu, Coprosma robusta (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETP]

Fresh holes in underside of leaf of Taupata, Coprosma repens (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae), note the black faecal droppings. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETG]

Holes in young leaves of Coprosma grandifolia (Rubiaceae) made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2EST]

Holes in leaves of round leaved coprosma, Coprosma rotundifolia (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETD]

There are many kinds of beetles in New Zealand. They can only be conclusively identified by an expert. Several small brown beetles may be found feeding on young leaves of Coprosma species, but the Coprosma flea beetle is the only one with enlarged femurs on their hind legs.

The presence of this kind of leaf damage in young leaves on Coprosma species in winter and spring is most likely to be caused by the Coprosma flea beetle, but could also be caused by weevils with seed feeding larvae, Praolepra species (Curculionoidea: Curculionidae). These beetles have a long 'snout' and do not have enlarged hind femora.

Adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETK]

Underside of adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETH]

Adult coprosma seed weevil, Praolepra sp. (Coleoptera: Curculionidae) feeding on Taupata, Coprosma repens (Rubiaceae). © All rights reserved. [Image: 2EJY]

Adult coprosma seed weevil, Praolepra sp. (Coleoptera: Curculionidae) feeding on Taupata, Coprosma repens (Rubiaceae). © All rights reserved. [Image: 2EJZ]

Holes in young expanding leaves of Glossy karamu, Coprosma robusta (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETR]

Holes in underside of leaves of Glossy karamu, Coprosma robusta (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae), note the black faecal droppings on the right hand leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETT]

Holes in young leaves of large seeded coprosma, Coprosma macrocarpa (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET0]

Holes in young leaves of thin leaved coprosma, Coprosma areolata (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET8]

No natural enemies of the Coprosma flea beetle are known. They are probably preyed upon by birds, spiders and predatory insects.

Adult Coprosma flea beetles feed on young leaves of Coprosma species (Rubiaceae).

Plant damage

They mainly feed on young leaves. Adult beetles chew small holes in leaves. On thicker leaves they mainly chew from the underside, but do not eat right through the leaf, leaving the skin (epidermis) on the far side of the leaf intact, so creating a 'window'. Beetles probably feed mainly at night but can be found feeding on leaves during the day.

Adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae) on leaf of Glossy karamu, Coprosma robusta (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETL]

Adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae) feeding on leaf of Glossy karamu, Coprosma robusta (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2ETP]

Holes in young leaves of tree coprosma, Coprosma arborea (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET5]

Holes in young leaves of thin leaved coprosma, Coprosma areolata (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET7]

Holes in young leaves of Coprosma grandifolia (Rubiaceae) made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ESZ]

Holes in young leaves of Coprosma grandifolia (Rubiaceae) made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ESY]

Holes in young leaves of shining karamu, Coprosma lucida (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETX]

Holes in underside of young leaves of shining karamu, Coprosma lucida (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETU]

Holes in young leaves of large seeded coprosma, Coprosma macrocarpa (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET1]

Holes in young leaves of Taupata, Coprosma repens (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET2]

Underside young leaf of Taupata, Coprosma repens (Rubiaceae), with holes made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ET4]

Fresh holes in underside of leaf of Taupata, Coprosma repens (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae), note the black faecal droppings. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETG]

Holes in young leaves of Coprosma rhamnoides (Rubiaceae) made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ESR]

Holes in young expanding leaves of Glossy karamu, Coprosma robusta (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETR]

Holes in underside of leaves of Glossy karamu, Coprosma robusta (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae), note the black faecal droppings on the right hand leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETT]

Holes in young leaves of round-leaved coprosma, Coprosma rotundifolia (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ETA]

Holes in young leaves of waxy-leaved coprosma, Coprosma tenuifolia (Rubiaceae), made by adult Coprosma flea beetle, Trachytetra rugulosa (Coleoptera: Chrysomelidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ESW]

Research project

The food plants of adults of this and some other chrysomelid beetles are known, but the egg laying site and food of the larvae are unknown. A simple and useful research project would be to collect adults and allow them to mate and lay eggs in pot plants of potential larval host plants. If the larvae can be reared and pupate then it would also be possible to describe the larvae and pupae. The potential host plants tested should include known adult host plants, closely related species and other plants growing in habitats where adults were present.

Kuschel G. 1990. Beetles in a suburban environment: A New Zealand case study. DSIR Plant Protection Report. No. 3: 1-118.

Samuelson GA 1973. Alticinae of Oceania (Coleoptera: Chrysomelidae). Pacific insects monograph 30: 1-165.

Dr Willy Kuschel and Dr Rich Leschen, who identified the adult beetles.

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

1 December 2018. NA Martin. Changed symbol used for apostrophes.