My bougainvilleas are being nibbled on by some little critter. It goes after the tender part of the leaf, so the plant is covered by half leaves. I’ve never been able to see any pests. I have no idea who’s the culprit.
— Anne Schubert
Woodland Hills
Recently, our part of the world has become a playground for the bougainvillea looper, which is the munching caterpillar or larval stage of a small moth. It is likely that this is the critter eating your plants.
The only time you can see bougainvillea loopers is very early in the morning, since they disappear as the sun rises. Certain bougainvilleas are more susceptible than others. My purple brasiliensis and crimson `Barbra Karst’ are being chewed while my neighbor’s dark pink `James Walker’ shows no caterpillar damage.
The bougainvillea looper was first spotted in Hawaii in the 1990s and arrived in San Diego a year or two ago, probably brought over by an unsuspecting air traveler. From there, it migrated to our area. Two organic insecticides are recommended for its control, Spinosad and Bt (Bacillus thuringiensis).
Spinosad is the most exciting insecticide to appear since the 1980s, when oil extracted from seeds of the tropical neem tree was turned into a powerful potion for control of a wide variety of insect pests.
Spinosad consists of metabolites produced by bacteria known as actinomycetes. If you keep a compost pile, you will undoubtedly have encountered actinomycetes. They appear as those thick white strands you often see when turning over the pile. You probably thought this white growth was some sort of fungus but it is actually a type of beneficial aerobic bacteria that assists in decomposition of organic material.
In any event, around 20 years ago, a vacationing scientist discovered a new species of actinomycetes growing in the soil of an abandoned rum distillery on the Caribbean island of St. Thomas. Since then, this exotic species of bacteria has yet to be found anywhere else on Earth. Meanwhile, though, the St. Thomas bacteria has been cultured on a commercial scale. Two of its metabolic by-products are mixed together and marketed as Spinosad.
Spinosad is effective primarily on caterpillars. When sprayed on the leaves of a plant infested with caterpillar pests, it causes the pests’ death within several days. In addition to bougainvillea loopers, other targets would include cabbage loopers and citrus leafminers.
Cabbage loopers are those thin green caterpillars that lay their eggs on fall and winter crops in the cabbage family, including broccoli, cauliflower and Brussels sprouts.
Citrus leafminers are another recently arrived pest in our area. They are tiny caterpillars that burrow through citrus leaves creating squiggly road map patterns.
An advantage of spraying Spinosad is that it is harmless to beneficial insects such as lady bugs, lacewings and parasitic wasps. Spinosad breaks down in sunlight in about a week so if caterpillars persist you may have to make one or two repeat applications at one week intervals.
Bt consists of spores and toxic proteins produced by a soil-dwelling bacteria discovered in Japan more than 100 years ago. Bt is also effective specifically on caterpillar and larval pests and is harmless to beneficial insects. However, Bt breaks down in sunlight more rapidly than Spinosad.
In one biotechnological development, the genes of the Bt bacteria that produce insect toxins have been inserted into the genome of crops — such as corn and cotton — that are susceptible to caterpillar pest damage. Once crops carry the Bt genes, they are not attacked by caterpillars and do not need to be sprayed with insecticide. Still, the possibility of insects overcoming their resistance to Bt and Spinosad remains.
Tip of the week
Aside from loopers, leafcutter bees also have started taking bites out of bougainvillea.
Since honeybee populations mysteriously have gone into decline, solitary carpenter and leafcutter bees have become more active.
Leafcutter bees remove neatly sawed, nearly circular foliar pieces from rose, bougainvillea, Bauhinia (orchid tree) and other smooth-leafed plants. These leaf pieces are used to line and seal off egg-laying chambers of the bees, found in the ground or in rotting wood.
Although leafcutter damage is disfiguring, it does not cause serious harm to plants and no remedial action is necessary.