Summer Activities

Green thistle beetle adult. Image - Jesse Bythell

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

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 as they mature.
Caterpillars can be harvested if you find them in good numbers. Cut off infested 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 present.

Check release sites for galls, which look like deformed lumps and range in size from 5 to 30 mm across.
If galls are present in good numbers, late spring to early summer is the best time to undertake harvesting and redistribution. Aim to shift at least 50 galls to each site and tie them onto plants so the tiny mites can shift across.

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.

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.
It should be possible to begin harvesting and redistribution at some 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.

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, 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. The white, star-shaped pupal cocoons may be visible on damaged foliage.
We would not expect you to find enough beetles to be able to begin harvesting and redistribution just yet.

Check release sites, especially the older ones. 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.

Releases only began in 2013, but there is no harm in checking release sites. 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.

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