By: Mary H. Dyer, Credentialed Garden Writer
Tortoise beetles are small, oval, turtle-shaped beetles that survive by chewing their way through the foliage of various plants. Fortunately, the pests usually aren’t present in large enough numbers to do serious damage, but they may chew unsightly holes throughout plant leaves. Read on for more information and tips for tortoise beetle control.
Tortoise Beetle Facts
Measuring only about l/4 inch (0.5 cm.), adult tortoise beetles are odd little bugs with several interesting adaptations that keep them safe from predators. For example, tortoise beetles have hard wing covers that they can clamp down tightly against a leaf surface. The covers also hide the head and legs, which makes the beetles more difficult for predators to grab hold of.
Tortoise beetles are often dark in color, but many have a distinctive metallic coloration – usually gold or orange – sometimes with black or red markings. They can actually alter their metallic color to blend in with the leaf surface.
The larvae, which are dull brown, green, or yellow with dark heads, have their own unique protective mechanism – they can glue debris, discarded skin, and poo together to form a sort of protective umbrella known as an anal fork.
What Do Tortoise Beetles Eat?
Tortoise beetles feed on various plants, including:
However, some species feast primarily on plants in the sweet potato family. This is generally where tortoise beetles do the most damage.
How to Get Rid of Tortoise Beetles
Seedlings are at higher risk, but most healthy, adult plants aren’t seriously threatened by tortoise beetles. Be sure plants are properly watered and fertilized, and that the planting area is clean and free of weeds. Although the damage is unsightly, it is usually minor.
In most cases, control of tortoise beetles is attained by simply removing the pests by hand. Avoid pesticides, if possible, because chemicals can kill ladybugs, parasitic wasps, and many other beneficial insects that keep tortoise beetles and larvae in check.
Serious infestations are easily controlled by residual insecticides, such as permethrin. However, chemical control is rarely necessary.
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Sweetpotato, kangkong ( Ipomoea aquatica ), and related Ipomoea species (plants in the morning glory family). Possibly, the beetles feed on crops and weeds in other families.
Adults feed on leaves, making small to medium-size holes (Photos 1-3). The larvae at first eat the leaf surface later, they eat their way through the leaf.
The oval eggs (1-2 mm long) are laid individually on the leaves in a small papery parcel. The larvae have spines, and an anal fork. The anal fork is made up of long spines near the tip of the abdomen, and these hold the old skins - which are not shed completely - mixed with excreta (faeces or "droppings"). The "tail" of old skins is carried over the back of the body, and can be moved about by the anal fork, probably to deter predators. The larvae pass through five moults, before a pupal stage develops. The pupae are attached by the tail end to the underside of a leaf.
The adults are about 5 mm diameter, oval and slightly flattened and squared at the shoulders (Photos 4&5). The head and appendages of the adult are mostly hidden by transparent parts of the thorax and the wing covers (Photos 2-5).
Common Insect Pests That Affect Tomatoes
At some point, every gardener encounters aphids. The tiny, green, pear-shaped bugs leave a sticky honeydew secretion behind them. They’re notorious sapsuckers of not only tomatoes but many other vegetables. A few aphids aren’t a problem, but when you start seeing clusters of them, it’s time to take action. An infestation will interfere with nutrients and water flowing up to your tomatoes leaves.
Fortunately, getting rid of aphids is not hard. They have soft bodies and no way to protect themselves. You can squish them with your thumb like a demi-God if you need an ego boost. Or you can take a more traditional route. Several OMRI and NOP sprays kill aphids. However, they’re mostly soap and fats, something you can mix up yourself at home on the cheap.
Ame’s Homemade Bug Spray
Here’s the mixture that I use. The mineral oil suffocates the aphids while the dish detergent dehydrates them. The peppermint oil acts as a natural repellent.
- Two cups of water
- Two tablespoons of food grade mineral oil
- Three drops of dish detergent
- Three drops of peppermint oil
Mix the ingredients in a spray bottle and apply to your plants. Shake the mixture frequently while applying because the oil will separate.
Natural Aphid Controls
Do you want Mother Nature to assist you with killing those aphids? Then encourage lady beetles. Lady beetles (or ladybugs) eat aphids when they are in the larvae stage. You can attract ladybugs to your garden by planting dill, chives, cosmos, marigolds, and yarrow. They also need places like trees and shrubs to hide from predators.
Flea beetles are tiny black insects with a hard exoskeleton. They can jump (hence the name flea beetle) and spread through your garden rapidly.
Flea beetles are my kryptonite! I’m convinced they spend all winter daydreaming of sucking the life out of my plants. They especially love to eat tomatoes and their cousins, eggplant and pepper.
You can identify flea beetle damage by the irregularly shaped pits and holes in the leaves of your tomatoes. Extensive damage makes the plant’s leaves look like lace. It sounds pretty, but it can destroy your plant.
Flea beetles lay eggs in the soil. The larva live underground and eat the plant’s roots. They typically don’t cause serious damage at this stage. As adults, they move above ground and eat the plant’s leaves. This stage is when they can cause monumental destruction.
Controlling Flea Beetles
You can help prevent flea beetles from attacking seedlings by using row covers when you transplant. Make sure to secure the row cover at ground level.
Sticky traps are an excellent way to control adults. I’ve seen diatomaceous earth (DE) recommended for flea beetles, but my experience is that it’s not effective. DE works best on soft-bodied pests. Diatomaceous earth consists of aquatic fossils. These ground-up organisms feel like flour in your hand. However, the microscopic jagged edges are lethal knives to soft-bodies critters. You can also t ry using Spinosad, which is an organic insecticide that kills flea beetles.
Flea beetles are attracted to radishes, which you can plant as a trap crop and then use traps or an insecticide to kill the tomato pests.
Root Knot Nematodes
There are thousands of varieties of nematodes, but the ones that mutilat your tomatoes are root-knot nematodes. These microscopic roundworms cause bumps or galls on the roots of your plants.
These galls interfere with the plant’s ability to take up nutrients. They may cause the plant to stop growing and turn yellow from lack of nutrients. Nematodes are widespread, but they’re more common in the south and coastal areas with warm winters.
Prevention of Nematodes
The best prevention is a strict crop rotation system. Nematodes can’t travel far, so removing hosts plants lowers the population. Leave three years between planting tomatoes in one spot.
Your grandmother, like mine, may have told you to plant marigolds with your tomatoes. That’s because marigolds act as a trap crop to attract nematodes. Research shows that the French types such as lemon drop, yellow boy, and tangerine are the most effective.
You can also purchase tomato varieties that are resistant to nematodes. When looking in catalogs, you may see VFN after a tomato variety. The N stands for nematode and means that type will be resistant.
Prevention of nematodes starts in the fall, so be sure to take steps to stop them from becoming a problem.
Pests of Sweetpotato
The sweetpotato flea beetle is the most common pest of sweetpotatoes in North Carolina. Soil-inhabiting pests lower grades or make potatoes unmarketable and are most economically important. Though the sweetpotato weevil is the most damaging pest of this crop nationwide, it has only recently been found in North Carolina and is a potential problem here.
Many pests attack sweetpotato foliage. In the plant bed, this injury can be threatening. In the field, however, there is little evidence that foliar pests do enough damage to warrant treatment.
A. Pests that feed on aboveground plant parts
- Caterpillars with three pairs of legs and five pairs of prolegs
- Southern armyworm – Gray or nearly black larva up to 36 mm long with greenish or pinkish tint lightly colored longitudinal stripes and paired triangular spots down back pale yellow head capsule with bright reddish-brown markings (Figure 1) feeds on leaves, tender stems, and tips of branches congregates round bases of plants during hot portion of the day
- Sweetpotato hornworm – First instar: white with black anal horn later instars: green or brown with black angled marks down each side and black anal horn body up to 90 mm long head green or brown with black stripes (Figure 2) defoliates plants often hides near base of plant under large leaves
- Yellowstriped armyworm – Pale gray to black caterpillar up to 45 mm long with yellow-orange stripes along each side and paired triangular spots on the back of most segments (Figure 3A) head capsule brown with black markings and a white inverted V (Figure 3B) feeds much like southern armyworm
- Potato leafhopper – Spinkle-shaped pest up to 3 mm long green body with yellowish to dark green spots (Figure 4) usually jumps instead of flies extracts sap from underside of leaf causing yellowing of leaf tips and margins one of several leafhopper species attacking sweetpotato
- Small fruit or vinegar fly – Small yellowish fly about 3 mm long with red eyes (Figure 5) hovers around overripe or decaying produce often found with small creamy maggots in the cracks of sweetpotatoes
- Sweetpotato flea beetle – Black oval beetle about 1.6 mm long with a bronze tinge, reddish-yellow legs, and deeply ridged wing covers (Figure 6) leaves narrow channels or grooves in upper surface of leaves injured areas turn brown and die
- Sweetpotato weevil adult and larva – Ant-like snout beetles are about 6 mm long with dark blue wing covers and red-orange legs and thorax fat, legless, dirty white larvae are about 9 mm long with pale brown head beetle makes small holes over surface of sweetpotatoes particularly at stem end larva tunnels inside filling tunnels with frass and causing sweetpotatoes to turn bitter. Feed on foliage, but primarily on underground plant parts
- Tortoise beetle adult and larva – Oblong-oval, basically gold-colored beetle, up to 8 mm long, with various black or red markings on its flattened, shell-like body (Figure 7A) larva with dull yellow, brown, or green body up to 12 mm long with black head, legs, spots, and spines long spines on larval abdomen hold excrement (Figure 7B) adult and larva chew leaves leaving them riddled with holes
- Spider mites – Tiny pale or reddish spider-like arthropods feed on the bottom of leaves (Figure 8) heavily infested plants become yellowish, bronzed or burned in appearance
B. Pests that feed on belowground plant parts
- Sweetpotato flea beetle larva – Slender, white, cylindrical larva, up to 5 mm long, with 3 pairs of legs near head (Figure 9) etches shallow, winding tunnels on surface of sweetpotato roots and sweetpotatoes tunnels darken, split, and leave scars
- Sweetpotato weevil adult and larva – Ant-like snout beetles are about 6 mm long with dark blue wing covers and red-orange legs and thorax (Figure 10A) fat, legless, dirty white larvae are about 9 mm long with pale brown head (Figure 10B) beetle makes small holes over surface of sweetpotatoes particularly at stem end larva tunnels inside filling tunnels with frass and causing sweetpotatoes to turn bitter
- White grub (spring rose beetle) – Dirty white grub up to 25 mm long with brown head and 3 pairs of legs near head (Figure 11) leaves large, shallow feeding scars on sweetpotatoes
- Wireworms – Several species of slender, wire-like larvae with 3 pairs of short legs near the head and a pair of prolegs at the tip of the abdomen large shallow cavities in sweetpotatoes - evidence of early injury deep ragged holes - later injury (Figure SS)
- Melanotus communis – Yellowish-brown with darker head body up to 25 mm long last abdominal segment with scalloped edges (Figure 12A)
- Southern potato wireworm – Cream colored or yellowish-gray with reddish-orange head body up to 17 mm long closed oval notch in last abdominal segment (Figure 12B)
- Tobacco wireworm – White with brown head body up to 19 mm long V-shaped notch in last abdominal segment (Figure 12C)
- Whitefringed beetle larvae – These yellowish-white legless, 12-segmented grubs, up to 13 mm in length, have small, pale heads. They gouge on roots, reducing marketable sweetpotatoes
Look for the golden round beetles, and the clear, wing margins that cover most of the head and thorax, and extend beyond the body, covering legs and other appendages.
Tortoise beetles are attacked by (chalcid) wasps in other countries, parasitic flies, and lady beetle larvae. It is likely that these parasites and predators attack tortoise beetles in Pacific island countries, but this is not known for certain.
The following is important:
- Avoid planting new crops next to those already infested with the beetles.
- Provide conditions for healthy, rapid plant growth, especially for vine cuttings after planting these may include manures, mulches and/or commercial fertilizers, and adequate water.
- Remove weeds (especially those in the Convolvulaceae family) from around the garden to reduce the beetle number.
- Harvest the infested crop, collect the vines and destroy them, and then plant a new crop.
None known, but fast-growing varieties are more likely to outgrow the damage caused by the beetles.
If chemical control is needed, do the following:
- Ash may be effective against sweetpotato tortoise beetles. Apply to the crop as soon as the pests are seen do not wait until the population is high. ( See Fact Sheet no. 56 ).
- Alternatively, add ½ cup of wood ash and ½ cup of lime in 4 L water leave to stand for some hours strain test on a few infested plants first to make adjustment to the strength before going into large-scale spraying.
- Use plant-derived products, such as derris, pyrethrum or chilli (with the addition of soap).
- Note, a variety of Derris , brought many years ago to Solomon Islands from Papua New Guinea, is effective as a spray. It contains rotenone, an insecticide, so it should be used with caution. There may be varieties of Derris (fish poisons) in your country that can be tried ( see Fact Sheet no. 56 ).
- Alternatively, synthetic pyrethroids are likely to be effective, but will also kill natural enemies.
AUTHORS Helen Tsatsia & Grahame Jackson
Photo 2 Graham Teakle, Canberra. Information from Chris Reid, Australian Museum, Sydney.
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.
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.
Pest Control Methods
Because the pesticides available to homeowners just aren't effective on eucalyptus pests, providing the proper cultural care is your best bet for preventing insect infestations. Eucalyptus plants grow best in full-sun locations with good soil drainage. Although drought-tolerant once established, these trees appreciate supplemental irrigation during prolonged dry spells. The experts at the University of California Integrated Pest Management Program suggest watering eucalyptus plants once a month with a drip hose until the top 12 inches of soil become moistened. Avoid fertilizing eucalyptus because these plants don't need extra nutrients to remain healthy and pests are often attracted to new plant growth. Promptly prune out and destroy any infested branches, but perform maintenance pruning when the pests are overwintering to avoid attracting insects to freshly cut wood tissue.