Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Spring Activities

Tradescantia damaged by the tip beetle larvae and adults.

Tradescantia damaged by the tip beetle larvae and adults.

Most biocontrol agents become active during spring, making it a busy time of year for biocontrol activities.

Broom leaf beetles (Gonioctena olivacea)

  • Check release sites by beating plants over a tray. Look for the adults, which are 2–5 mm long and goldish-brown (females) through to orangey-red (males). Look also for greyish-brown larvae that may also be seen feeding on leaves and shoot tips.
  • It is probably still a bit soon to begin redistribution.

Broom shoot moth (Agonopterix assimilella)

  • Late spring is the best time to check release sites. Look for the caterpillars’ feeding shelters made by webbing twigs together. Small caterpillars are dark reddish-brown and turn dark green as they get older. We have only found evidence of establishment at one site in Southland to date, so we will be interested to hear if you find any sign of the caterpillars.
  • We would not expect you to be able to begin redistribution just yet.

Green thistle beetles (Cassida rubiginosa)

  • Check release sites for adult beetles which are 6–7.5 mm long and green, so are quite well camouflaged against the leaf. Adults and larvae make windows in the leaves. Larvae have a protective covering of old moulted skins and excrement. You may also see brownish clusters of eggs on the underside of leaves.
  • It should be possible to begin redistribution at some sites. Use a garden-leaf vacuum machine and aim to shift at least 50 adults in the spring. Be careful to separate the beetles from other material collected, which may include pasture pests.

Ragwort plume moth (Platyptilia isodactyla)

  • October is the best time to check release sites for caterpillars. Look for plants with wilted or blackened or blemished shoots with holes and an accumulation of debris, frass or silken webbing. Pull back the leaves at the crown of damaged plants to look for large hairy, green larvae and pupae. Also check where the leaves join bolting stems for holes and frass. Don’t get confused by larvae of the blue stem borer (Patagoniodes farinaria), which look similar to plume moth larvae until they develop their distinctive bluish colouration.
  • If the moth is present in good numbers the best time to shift it around is in late spring. Dig up damaged plants, roots and all. Pupae may be in the surrounding soil so retain as much as possible. Shift at least 50–100 plants, but the more the better. Place one or two infested plants beside a healthy ragwort plant so any caterpillars can crawl across.

Tradescantia leaf beetle (Neolema ogloblini)

  • Check release sites for the slug-like larvae in areas where there is damage to the leaves. The larvae graze the epidermal tissue off the leaves, mostly on the undersides, and can skeletonise them. The dark metallic bronze adults may be hard to spot as they tend to drop when disturbed. Adults chew holes around the edges of leaves, and may consume entire leaves.

Tradescantia stem beetle (Lema basicostata)

  • Most release sites are still fairly new but there is no harm in looking. The black knobbly adults also tend to drop when disturbed, but look for their feeding damage, which consists of elongated windows in the upper surfaces of leaves or sometimes whole leaves consumed. The larvae inside the stems will also be difficult to spot. Look for stems showing signs of necrosis or collapse and brown frass.

Tradescantia tip beetle (Neolema abbreviata)

  • Releases only began earlier this year, but again there is no harm in looking. The adults are mostly black with yellow and black wing cases, but like the other tradescantia beetles tend to drop when disturbed. Larvae will also be difficult to see when they are feeding inside the tips, but brown frass may be visible. When tips are in short supply the slug-like larvae feed externally on the leaves.

Other agents

You might also need to check or distribute the following this spring (for further details see the Biological Control of Weeds Book):

  • Boneseed leafroller (Tortrix s.l. sp. “chrysanthemoides”)
  • Broom seed beetles (Bruchidius villosus)
  • Gorse soft shoot moth (Agonopterix ulicetella)
  • Gorse thrips (Sericothrips staphylinus)
  • Gorse colonial hard shoot moth (Pempelia genistella)
  • Woolly nightshade lacebug (Gargaphia decoris)

Send any reports of interesting, new or unusual sightings to Lynley Hayes.