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• Issue 78 »
• Summer Activities

Summer Activities

Male broom leaf beetle (Gonioctena olivacea).

Most biocontrol agents become active during spring, making it a busy time of year to check release sites and move agents around.

Boneseed leafroller (Tortrix s.l. sp. “chrysanthemoides”)

• Check release sites for feeding shelters made by caterpillars webbing together leaves at the tips of stems. Also look for ‘windows’ in the leaves and sprinkles of black frass. Small caterpillars are olive green in colour and become darker, with two parallel rows of white spots as they mature.
• Caterpillars can be harvested if you find them in good numbers. Cut off infested boneseed tips and wedge them into plants at new sites. Aim to shift at least 500 caterpillars to sites where scale insects and invasive ants are not known to be present.

Broom gall mites (Aceria genistae)

• Check release sites for galls, which look like deformed lumps and range in size from 5 to 30 mm across. Very heavy galling, leading to the death of bushes, has already been observed at some sites.
• Harvesting of galls is best undertaken from late spring to early summer when predatory mites are less abundant. If galls are present in good numbers, aim to shift at least 50 to each site and tie them on to plants so the tiny mites can shift across.

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), with stripes on their backs. Look also for greyish-brown larvae, which may also be seen feeding on leaves and shoot tips.
• It is probably still a bit soon to begin harvesting and 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 are unsure if this moth has managed to successfully establish in New Zealand, 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 harvesting and redistribution just yet.

Green thistle beetles (Cassida rubiginosa)

• Check release sites for adult beetles, which emerge on warm days towards the end of winter and feed on new thistle leaves, making round window holes. The adults are 6–7.5 mm long and green, but are quite well camouflaged against the leaf. The larvae also make windows in the leaves. They have a protective covering of old moulted skins and excrement. You may also see brownish clusters of eggs on the undersides of leaves.
• It should be possible to harvest beetles at many of the older sites. Use a garden-leaf vacuum machine and aim to shift at least 50 adults from spring throughout summer and into autumn. Be careful to separate the beetles from other material collected, which may include pasture pests.

Lantana blister rust (Puccinia lantanae)

• Check sites where lantana plants infected with blister rust have been planted out, especially after a period of warm, wet weather. Signs of infection include leaf and stem chlorosis (yellowing) accompanied by large, dark pustules on the undersides of leaves and on the stems. Stunting, defoliation and die-back may also be apparent.
• Once established, this rust is likely to be readily dispersed by the wind. If redistribution efforts are needed, the best method is likely to involve placing small potted lantana plants beneath infected ones and then planting these out at new sites once they have become infected. However, to propagate and distribute lantana in this manner an exemption from MPI will be required.

Lantana leaf rust (Prospodium tuberculatum)

• Check sites where the leaf rust has been released, especially after a period of warm, wet weather. Look for yellowing on the leaves with corresponding brown pustules and spores, rather like small coffee granules. A hand lens may be needed to see the symptoms during early stages of infection.
• Once established, this rust is likely to be readily dispersed by the wind. If redistribution efforts are needed, the best method will likely involve harvesting infected leaves, washing them in water to make a spore solution and then applying this to plants.

Privet lace bug (Leptoypha hospita)

• Although it is early days for privet lace bug releases it might be worth checking release sites to look for any signs post winter. Examine the undersides of leaves for the adults and nymphs, especially leaves showing signs of bleaching.
• It is likely to be too soon for any harvesting to begin.

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 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 that any caterpillars can crawl across.

Tradescantia leaf beetle (Neolema ogloblini)

• Check release sites for the shiny metallic bronze adults sitting on the foliage, or the larvae, which have a distinctive protective covering over their backs. Also look for notches in the edges of leaves caused by adult feeding, or leaves that have been skeletonised by larvae grazing off the green tissue. The white, star-shaped pupal cocoons may also be visible on damaged foliage.
• If you can find plenty of beetles then harvesting can begin. Aim to collect and shift 50–100 beetles. Collect the beetles either using a suction device or a small net.

Tradescantia stem beetle (Lema basicostata)

• Check release sites for the black knobbly adults, which tend to drop when disturbed and can be difficult to see. Look also 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.
• If you can find widespread damage at the site then you may be able to begin harvesting. We still need to identify the best possible method to do this. If it proves to be too difficult to collect 50–100 adults with a suction device, then another approach to try would be to remove a quantity of the damaged material and put it in a wool pack or on a tarpaulin and wedge this into tradescantia at new sites. However, to distribute tradescantia in this manner an exemption from MPI will be required.

Tradescantia tip beetle (Neolema abbreviata)

• Check the release site for the adults, which are mostly black with yellow wing cases, sitting about on the foliage. Look also for their feeding damage, which looks like elongated windows in the leaves, similar to those made by the stem beetle. 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.
• If you can find plenty of beetles then harvesting can begin. Aim to collect and shift 50–100 beetles. Collect the beetles using either a suction device or a small net.

Other agents

You might also need to check or distribute the following this spring:

• gorse soft shoot moth (Agonopterix ulicetella).
• gorse thrips (Sericothrips staphylinus).
• gorse colonial hard shoot moth (Pempelia genistella).

National Assessment Protocol

For those taking part in the National Assessment Protocol, spring is the appropriate time to check for establishment and/ or assess population damage levels for the species listed in the table below. You can find out more information about the protocol and instructions for each agent at: www.landcareresearch.co.nz/publications/books/biocontrol-of-weeds-book

Send any reports of interesting, new or unusual sightings to Lynley Hayes (hayesl@landcareresearch.co.nz, Ph 03 321 9694).