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Three-Lined Potato Beetle

Lema daturaphila

Three-Lined Potato Beetle, Tobacco Slug

A close up photograph of a Lema daturaphila three-lined potato beetle on a plant
Lema daturaphila1 by Ibsut (CC BY 2.0)
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The Three-Lined Potato Beetle is a small, stripey, black and yellow insect that may be found on plants in the Nightshade family (Solanaceae). Although, they're most commonly seen eating Cape Gooseberry, Tobacco and tomatillo. The larvae look like small, creamy, grubs; however, cover themselves in their own faeces. They do this for camouflage, so watch out for these masters of disguise when you next inspect your Nightshade plants! It's likely their bright yellow colouration evolved as an adaptation to warn predators of their foul taste, which is a result of their high-toxin diets!
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Traits

Adult beetles and larvae share the same host plant, so could be potentially damaging if present in large numbers.
These beetles are a major pest in agriculture.

Appearance

The adults are just shorter than 1cm. They're distinctively vibrant, boasting yellow, orange and black vertical stripes. More specifically, they possess three dark lines, one per elytral margin, and one crossing the centre between both wings. This is where these beetles get their common names from. Larvae look like small creamy grubs with brown heads (roughly 7mm). They cover themselves in their excrement, so could be mistaken for some dirt, or bird faeces!

Symptoms

They will leave holes in tree leaves following feeding. In large numbers, these beetles may deplete a whole leaf.

Activity

Diurnal

Personality

Order

Coleoptera

Family

Chrysomelidae

Metamorphosis

Complete

Distribution

Native to South America, now present in South Africa

Biological treatment

Picking these beetles of plants as and when they're seen is probably one of the best modes of action. Regularly inspecting leaves for bright yellow eggs and removing them as and when will help to prevent large outbreaks. It's thought that trenches dug between rows of potato plants can capture adults travelling between crops. Slopes should be steeper than 45 degrees and lining them with plastic will make surfaces more slippery. Another tip for reducing beetle movement between plants would be to mulch 5-7cm of straw or hay as soon as plants sprout. Using some polyester sheets as a barrier during the Spring would add an additional layer of protection against adults in the springtime. Diatomaceous earth is non-toxic, yet acts as a barrier against things such as beetles, caterpillars and slugs. Take care during the application, be sure the eyes are protected and none is inhaled. If available, beneficial nematodes can be watered into the soil. These will eradicate all the grubs in the area covered, including beneficial larvae too.

Chemical treatment

If you have exhausted all the biological options, then you can try to spot-treat plants with organic pyrethrums. Organic pesticides are thought to be more environmentally benign than synthetic insecticides. These contain pyrethrums, fatty oils and plant essential oils. If the infestation is considered most severe, you might want to try synthetic pyrethroids. They are more aggressive in their mode of action but can be applied to plants less frequently. They're also unselective, so will most likely kill any insect that comes into contact with it.

Attracts

Despite their names, these insects are seldom found on potato! They prefer the leaves of tomatillo.

Tomatillo

Physalis philadelphica

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