Photo 1. Brown faecal spots, adults and nymphs of the bean lace bug, Corythucha gossypii, on eggplant.
Photo 2. Leaves of eggplant showing white flecks, and also more serious yellow-white bleaching of older leaves due to feeding of bean lace bug, Corythucha gossypii.
Photo 5. Dark brown patch on the underside of a bean leaf due to feeding of the bean lace bug, Corythucha gossypii.
Bean lace bug, cotton lace bug
Widespread. North America (Hawaii, possibly Florida), and (restricted) Central and South America, and the Caribbean, Oceania. It is recorded from American Samoa, Samoa.
Beans, bele, breadfruit, eggplant, Hibiscus, and many other hosts. CABI lists soursop and sweetpotato.
Nymphs and adults feed on the leaves sucking the sap with piercing mouthparts. In the process, brown faecal spots occur on the underside of the leaves (Photo 1), which also show white spots, large brown dead patches or yellow-white bleaching (Photo 2), depending on the host, and may fall early.
The oval eggs are inserted into the underside of leaves in circular groups and covered in faecal matter. The nymphs are brown with black markings, and there are five stages (Photo 3). The adults are grey, about 3-4 mm long and 2 mm wide, with semi-transparent areas in the wings that give the "lace-like" appearance (Photo 4). They have a plate-like structure behind the head which covers the thorax and comes to a point over the wings. These structures have short spines. The life cycle is complete in 3 weeks or less.
Usually, the damage is small, but when populations are high, in dry hot weather, the top surface of beans show stippling (small white marks) and large brown patches. Leaves of eggplant become bleached, turning a pale whitish yellow (Photo 2). The leaves may drop earlier than normal.
On eggplant, damage from above is similar to leaves infested by mites, but mite infestations invariably show webbing.
On bean, look for the dark brown patches on the underside of leaves (Photo 5), and speckling and large light brown patches above, that coincide with the damage underneath (Photo 6). On eggplant, look at the top surface of younger leaves for numerous small white flecks, and large patches of yellowish white on older leaves between veins that are still green. Look at the undersurface of the leaves for the grey lace bugs, about 3 mm long, and look for the brown dots of feacal matter on both hosts.
Lace bugs are usually kept under control by natural enemies of which there are several kinds. They include parasitic wasps, assassin bugs, lacewing larvae, ladybird beetles, pirate bugs, and more. To attract natural enemies, grow flowering plants nearby. And if applying pesticides, use those without long-term residual activity.
In general, ensure that the crop is healthy: provide adequate nutrients - manures or inorganic fertilizers - and preserve water with organic mulches. This will help plants tolerate the damage done by lace bugs, particularly in dry times.
In most instances, populations of lace bugs will not be high enough to require the use of insecticides. If they are needed, use "soft" options first, and if they do not provide adequate control test commercial products, contact or systemic insecticides. The "soft" options are:
Commercial products (e.g., horticultural oil) containing petroleum oil; follow the instructions on the product label. Make sure the oil can be used on the crops of interest, otherwise, it may damage the foliage.
These sprays work by blocking the breathing holes of insects causing suffocation and death. Spray the underside of leaves as the soaps and oils must contact the lace bugs. The sprays will need to be repeated after a few days, as the eggs may not be susceptible to "soft" insecticides.
AUTHOR Grahame Jackson
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community. Photo 3 Mike Furlong, University of Queensland, Brisbane.
This fact sheet is a part of the app Pacific Pests and Pathogens
The mobile application is available from the Google Play Store and Apple iTunes.