Summer Activities

Female broom leaf beetle and egg.

Summer is a busy time for many of our biocontrol agents. Some activities you may need to schedule over the next few months 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. Caterpillars makes “windows” in the leaves where they have eaten the green tissue away, leaving behind sprinkles of black frass and the leaves may be turning brown. Small caterpillars are olive-green in colour and become darker, with two parallel rows of white spots as they mature. We would be very interested to hear if you find any severe damage to boneseed foliage.
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 mite (Aceria genistae)

Summer is a good time to check plants at release sites for galls, which look like deformed lumps and range in size from 5 to 30 mm across. They will probably be fairly close to the release point. Occasionally galls can be found on broom that are not made by the gall mite, but these are much less dense. We are happy to help confirm the identity of any galls you find.
Because the mites are showing much promise, but are expected to disperse quite slowly, it will be important to plan a comprehensive redistribution programme once you have good numbers. Note that October–November is the best time for harvesting and redistribution, when mite numbers are building inside the galls. However, it may still be possible to successfully move the galls around in December if the weather is not too hot and dry. Aim to shift at least 50 galls, and tie them onto plants in bunches of 10 galls per plant at the new site so the tiny mites can shift across.

Broom leaf beetles (Gonioctena olivacea)

Check sites where beetles have been released for three or more years for signs of establishment. The adults are 2–5 mm long and females tend to be goldish-brown while males have an orangey-red tinge, although colouration can be quite variable. These beetles can be quite hard to find so it is best to use a beating tray and don’t be surprised if you only find one or two. The adults lay eggs over a period of 3–4 months, starting in spring, so you may also be able to find the greyish-brown larvae feeding on the leaves or shoot tips.
It is probably still a bit soon to find enough beetles to be able to begin harvesting and redistribution just yet.

Broom seed beetle (Bruchidius villosus)

Beetles can be harvested and redistributed while they are still inside mature brown pods but avoid green ones as the beetles will not be completely developed. Cut infested branches and wedge them into bushes at the new site. A period of hot weather can cause pods to ripen rapidly, so once the first ones have started to burst, don’t delay.

Gorse soft shoot moth (Agonopterix ulicetella)

Check release sites now as, by late November – early December, the caterpillars will be quite large but not yet pupated. Look inside webbed or deformed growing tips for dark brown or greyish-green caterpillars. We would be very interested to hear of any outbreaks or caterpillars found in new locations – areas of particular interest are the North Island and lower South Island.
Redistribute caterpillars by harvesting infested branches or even whole bushes.

Green thistle beetles (Cassida rubiginosa)

Check release sites for windows eaten into the leaves made by the adults and larvae. Adults are well camouflaged, being green, so it may be easier to spot the larvae, which have a distinctive protective covering of old moulted skins and excrement, and prominent lateral and tail spines.
If you find beetles in good numbers then make plans to harvest adults next spring.

Hieracium gall midge (Macrolabis pilosellae)

Check release sites for plants with swollen and deformed leaves caused by larval feeding. Summer is not a good time to redistribute this agent as whole infected plants must be moved and it is crucial that they do not dry out.

Tradescantia leaf beetle (Neolema ogloblini)

Check the older release sites for signs of the beetles, such as 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 but they tend to drop or fly away when disturbed. It may be easier to spot the larvae, which have a distinctive protective covering over their backs. Look on the underside of damaged leaves for signs of young larvae which are gregarious and may be seen in packs forming feeding fronts. Older larvae feed individually. The pupal cocoons are extremely unusual (white, star-shaped and resemble styro-foam) and may be visible on damaged foliage. We would be very interested to hear if you find any sign of the beetles.
We would not expect you to find enough beetles to be able to begin harvesting and redistribution just yet.

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.
We would not expect you to find enough beetles to be able to begin harvesting and redistribution just yet.

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 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.
We would not expect you to find enough beetles to be able to begin harvesting and redistribution just yet.

Woolly nightshade lace bug (Gargaphia decoris)

Check release sites by examining the undersides of leaves for the adults and nymphs, especially on leaves showing signs of bleaching or black spotting around the margins.
We expect the lace bugs might also be slow to disperse so if good numbers are present it would be worth collecting some to release in other areas. Always wear gloves when handling woolly nightshade foliage to avoid any health issues. Cut leaf material that is infested with adults and/or nymphs and wedge or tie this material firmly into new woolly nightshade plants so the lace bugs can move across. We recommend that you shift at least 1000 individuals to each new site at any time during the warmer months.

Other agents

You might also need to check or distribute the following this summer (for further details see The Biocontrol of Weeds Book):

If you are making an effort to keep your copy of The Biological Control of Weeds Book – Te Whakapau Taru up to date you need to go online and download some new and revised pages: