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• Issue 75 »
• Autumn Activities

Autumn Activities

Drawing by Susan Marks.

There are a few things you might want to fit in before the wind-down towards winter. We would be very interested to hear about what you find.

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 left until spring when predatory mites are less abundant.

Gall-forming agents

• Early autumn is the best time to check release sites for many gall-forming agents. If you find large numbers of galls caused by the mist flower gall fly (Procecidochares alani) and hieracium gall wasp (Aulacidea subterminalis), you could harvest mature specimens and release them at new sites.
• Do not collect galls caused by the hieracium gall midge (Macrolabis pilosellae) as this agent is best redistributed by moving whole plants in the spring.
• At nodding and Scotch thistle gall fly (Urophora solstitialis and U. stylata) release sites look for fluffy or odd-looking flowerheads that feel lumpy and hard when squeezed. Collect infested flowerheads and put them in an onion or wire mesh bag. At new release sites hang bags on fences, and over winter the galls will rot down, allowing adult flies to emerge in the spring.
• At Californian thistle gall fly (Urophora cardui) release sites look for swollen deformities on the plants. Once these galls have browned off they can be harvested and moved to new sites (where grazing animals will not be an issue) using the same technique as above.

Tradescantia leaf beetle (Neolema ogloblini)

• Check release sites, especially older ones. You may see 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, especially 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. 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, the 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 the Ministry for Primary Industries will be required.

Tradescantia tip beetle (Neolema abbreviata)

• Check release sites, especially 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 maybe visible. When tips are in short supply, the slug-like larvae feed externally on the leaves.
• If you can see 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.

Woolly nightshade lace bug (Gargaphia decoris)

• Check release sites by examining the undersides of leaves for the adults and nymphs, especially of leaves showing signs of bleaching or black spotting around the margins.
• It is probably best to leave any harvesting until spring.

National Assessment Protocol

For those taking part in the National Assessment Protocol, autumn 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.