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• Issue 89 »
• Spring Activities

Spring Activities

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

Tutsan beetle larva and damage

Broom leaf beetles (Gonioctena olivacea)

• We think this beetle has established quite widely but is not abundant and we are keen to know more about this. Look for beetles by beating plants over a tray. The adults 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.
• The beetles can be harvested if you find them in good numbers. Aim to shift at least 100−200 beetles to sites that are not yet infested with gall mites.

Broom shoot moth (Agonopterix assimilella)

• We are unsure if this moth has managed to successfully establish in New Zealand, so we will be interested to hear if anyone can find any sign of them. Late spring is the best time to check release sites, so 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.

Darwin’s barberry weevil (Berberidicola exaratus)

• Since these weevils are difficult to mass-rear we are attempting to establish them at a couple of field sites from which they can later be harvested and redistributed to all areas where they are needed. We are therefore very interested to know if establishment can be confirmed.
• Beat plants at release sites later in the spring to see if any of the small (3−4 mm long), blackish adults can be found. Also examine the fruits for signs of puncturing. Please let us know what you find.

Giant reed gall wasp (Tetramesa romana)

• Although it is early days, it is worth checking release sites this spring to look for swellings on the stems caused by the gall wasps. These look like small corn cobs on large, vigorous stems, or like broadened, deformed shoot tips when side shoots are attacked. The galls often have small, circular exit holes made by emerging wasps.
• It will probably be too soon to consider harvesting and redistribution if you do see evidence of the gall wasp establishing.

Japanese honeysuckle white admiral (Limenitis glorifica)

• Look for the adult butterflies at release sites from late spring. Look also for pale yellow eggs laid singly on the upper and lower surfaces of the leaves, and for the caterpillars. When small, the caterpillars are brown and found at the tips of leaves, where they construct pontoon-like extensions to the mid-rib. As they grow, the caterpillars turn green with spiky, brown, horn-like protrusions.
• Unless you find lots of caterpillars, don’t consider harvesting and redistribution activities. You will need to aim to shift at least 1,000 caterpillars to start new sites. The butterflies are strong fliers and are likely to disperse quite rapidly without any assistance.

Lantana blister rust (Puccinia lantanae)

• We do not yet have any evidence that the blister rust has established and are keen to hear if symptoms can be found in the field. 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 is needed, this will require 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 the Ministry for Primary Industries (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. If the rust is well established, then extensive defoliation may be obvious.
• Once established, this rust is likely to be readily dispersed by the wind. If redistribution efforts are needed, the best method is to harvest infected leaves, wash them in water to make a spore solution, and then apply this to plants.

Privet lace bug (Leptoypha hospita)

• Examine the undersides of leaves for the adults and nymphs, especially leaves showing signs of bleaching.
• If large numbers are found, cut infested leaf material and put it in chilly bin or large paper rubbish bag, and tie or wedge this material into Chinese privet at new sites. Aim to shift at least 1,000 individuals to each new site.

Ragwort plume moth (Platyptilia isodactyla)

• October is the best time to check release sites for caterpillars, so look for plants with wilted, 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 coloration.
• 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, stem and tip beetles (Neolema ogloblini, Lema basicostata, N. abbreviata)

• Look for the distinctive feeding damage and adults. For the leaf and tip beetles, look for the external-feeding larvae, which have a distinctive faecal shield on their backs.
• If you find them in good numbers, aim to collect and shift at least 100–200 beetles using a suction device or a small net. For stem beetles it might be easier to harvest infested material and wedge this into tradescantia at new sites (but make sure you have an exemption from MPI that allows you to do this).

Tradescantia yellow leaf spot (Kordyana brasiliensis)

• Although the fungus has only been released a short time at many release sites, promising signs of likely establishment have been seen at some sites after only a few months, so it is worth taking a look this spring. Look for the distinctive yellow spots on the upper surface of the leaves with corresponding white spots underneath, especially after wet, humid weather. Feel free to take a photo to send to us for confirmation if you are unsure, as occasionally other pathogens do damage tradescantia leaves.
• The fungus is likely to disperse readily via spores on air currents. If human-assisted distribution is needed in the future, again you will need permission from MPI to propagate and transport tradescantia plants. These plants can then be put out at sites where the fungus is present until they show signs of infection, and then planted out at new sites.

Tutsan beetle (Chrysolina abchasica)

• It is early days for most tutsan beetle release sites, but the best time to look for this agent is spring through to mid-summer. Look for leaves with notched edges or whole leaves that have been eaten away. The iridescent purple adults are around 10−15 mm in size, but they spend most of the day hiding away so the damage may be easier to spot. Look also for the creamy-coloured larvae, which are often on the underside of the leaves. They turn bright green just before they pupate

Tutsan moth (Lathronympha strigana)

• We do not yet know if the tutsan moth has established so are keen to hear how they are doing in the field.  Look for the small orange adults flying about flowering tutsan plants. They have a similar look and corkscrew flight pattern to the gorse pod moth (Cydia succedana). Look also for fruits infested with the larvae.

Other agents

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

• boneseed leafroller (Tortrix s.l. sp. “chrysanthemoides”)
• broom gall mites (Aceria genistae)
• gorse colonial hard shoot moth (Pempelia genistella)
• green thistle beetle (Cassida rubiginosa)
• gorse soft shoot moth (Agonopterix ulicetella)
• gorse thrips (Sericothrips staphylinus)

National Assessment Protocol

For those taking part in the National Assessment Protocol, spring is the appropriate time to check for establishment and/or to 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

CONTACT: Lynley Hayes (hayesl@landcareresearch.co.nz).