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• Issue 74 »
• Summer Activities

Summer Activities

Drawing by Susan Marks.

Summer is a busy time in the world of biocontrol. Some activities you may need to schedule are listed below.

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. Heavily galled plants may be dead or dying.
• If galls are present in good numbers, late spring – early summer is the best time to undertake harvesting and redistribution. Because the mites are showing much promise but are expected to disperse quite slowly, it will be important for all regions with a major broom problem to plan a comprehensive redistribution programme. Aim to shift at least 50 galls to each site and tie them onto 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 that may also be seen feeding on leaves and shoot tips.
• It is probably still a bit soon to begin harvesting and redistribution.

Green thistle beetles (Cassida rubiginosa)

• Check release sites for adult beetles, which are 6–7.5 mm long and green and 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 underside 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. Please let us know if you discover an outbreak.

Tradescantia leaf beetle (Neolema ogloblini)

• Check release sites, especially the older ones. 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. You may see the dark metallic bronze adults sitting on the foliage or the larvae, which have a distinctive protective covering over their backs. The white, star-shaped pupal cocoons may also be visible on damaged foliage.
• Redistribution has begun at some of the older sites. If you can see plenty of beetles sitting about then harvesting can begin. Aim to collect and shift 50–100 beetles. Collect the beetles either using a beating tray or a small net.

Tradescantia stem beetle (Lema basicostata)

• Check release sites, especially the older ones. The black knobbly adults tend to drop when disturbed, and can be difficult to see. 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.
• If you can find widespread damage at the site then you may be able to begin harvesting and redistribution. We still need to identify the best possible method to do this. We suggest trying to remove a quantity of the damaged material and putting in a wool pack or on a tarpaulin and wedging this into tradescantia at new sites. However, to distribute tradescantia in this manner an exemption from the Ministry for Primary Industries will be required.

Tradescantia tip beetle (Neolema abbreviata)

• Check release sites, especially the older ones. The adults are mostly black with yellow wing cases, and you may see them sitting about on the foliage. Look also for their feeding damage, which looks like elongated windows in the leaves, similar to 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.
• We expect it is probably still a bit soon to begin harvesting and redistribution just yet.

National Assessment Protocol

For those taking part in the National Assessment Protocol, summer 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: The Biological Control of Weeds Book.