Cucumber beetle is the common name given to members of the genus Acalymma and Diabrotica. The most common cucumber beetles are the striped cucumber beetle (Acalymma vittatum). And the spotted cucumber beetle (Diabrotica undecimpunctata howardi). These beetles can be serious pests on cucurbit plants in your garden.
In this article, we will cover everything you need to know about cucumber beetles. This includes understanding the life cycle. So, you know when certain life stages are present and where to find them. We will then discuss the damage they cause, prevention methods, and how to get rid of them.
Cucumber Beetle Life Cycle
The cucumber beetle’s life cycle consists of four distinct stages of growth. The egg, larva, pupa, and adult. This process is known as complete metamorphosis. Typically, there are two generations of cucumber beetles per year. Though a few states have reported these beetles having only 1 or up to 3 generations.
Cucumber beetle eggs are yellow to orange in color, oval-shaped, and around .5mm in size. The first generation of eggs is laid between late April and early June. After soil temperatures are around 55 degrees Fahrenheit. Striped cucumber beetles will lay up to 4 eggs in a cluster at the base of cucurbit plants. While spotted cucumber beetles will deposit clusters of 25 to 50 eggs on the bottom surface of leaves. Eggs develop and hatch in as little as 6 to 9 days, though colder temperatures can cause them to develop slower.
Larvae of both species begin feeding on cucurbit roots and stems near the soil after hatching. Cucumber beetle larvae appear wormlike with cream-colored bodies and a brown head capsule. They grow through 3 larval instars in 2 to 4 weeks. They shed their skin between each instar and reach a length of 10 to 12mm.
Cucumber beetles will exit their host plant and dig into the soil near the base to pupate. Pupae are whitish, turning yellowish as they age. Pupation takes around 6 to 10 days.
First-generation adults leave the soil and begin feeding on cucurbits and mating. Producing a second generation during mid to late summer. Second-generation adults will leave the soil and feed, but don’t start reproducing. Instead, as food sources become scarce and winter temperatures set in, they will find a place to overwinter. Normally under leaves or other woody debris.
In March of the following year, overwinter adults will emerge and begin feeding. They will feed on alternate hosts until the cucurbits they prefer become available. Mating usually begins 2 to 3 weeks after adults emerge from overwintering.
Signs Of Cucumber Beetles
Adults will feed on leaves, flowers, pollen, and fruit rinds. You’ll notice holes in leaves and complete defoliation of small plants. Or damaged flowers that may fail to open or fall off. While fruits are still edible after cucumber beetle feeding, the scarring left on fruit rinds makes them unappealing to most consumers. Their feeding damage, and the diseases they spread, can also cause plants to wilt and yellow.
Larvae feed on roots and stems which can also cause wilting and yellowing of plants. You may notice plants falling over near the soil surface due to weakened stems from feeding. Larval feeding can also kill seedlings and transplants.
Damage Caused By Cucumber Beetles
Damaged caused by cucumber beetle feeding provides signs to let you know they’re present. Before we cover some of the other damage they cause, it is important to know which plants are impacted by cucumber beetles.
So what do cucumber beetles eat? They prefer cucurbit plants including cucumbers, squash, pumpkins, and watermelons. However, most of these plants are absent when adults emerge from overwintering. These adults will feed on pollen and leaves of alternate host plants. Such as nightshade plants (including tomatoes), apple trees, goldenrod, asters, hawthorn trees, and willow trees. Larvae feed exclusively on cucurbit plants.
Feeding damage doesn’t just impact the appearance of plants. Cucumber beetles can transmit a variety of diseases. Such as cucumber mosaic virus, squash mosaic virus, maize chlorotic mottle virus, and bean mosaic virus. They can also transmit bacterial wilts including Erwinia tracheiphila and Pseudomonas lachrymans. While mosaic viruses can cause distortions and discoloration of plant tissue, bacterial wilts typically result in plant death.
How To Prevent Cucumber Beetles
Since adult beetles fly, there’s no way to guarantee that one of these beetles won’t find its way into your garden. However, there are several ways to reduce the odds. Removing alternate host plants in the area can prevent attracting adults to the area in early spring. Planting your cucurbit plants later in the season, usually in mid-June, can reduce beetle populations.
Similar to Japanese beetles, you can prevent cucumber beetle damage by placing cucurbits under row covers (netting) to exclude beetles from getting to them. This is especially important during peak cucumber beetle season when plants are small and can’t handle much feeding damage. For more information on Japanese beetles, check out our article.
What Repels Cucumber Beetles?
Plants that have been shown to repel cucumber beetles include radish, tansy, and nasturtium. They should be planted as companion plants of cucurbits to keep them away. Companion plants are planted together to improve each other’s growth and/or to reduce pest issues.
Aluminum mulch or reflective plastic mulch has been shown to reduce cucumber beetle populations. They work by reflecting light which interferes with visual cues insects use to find plants. They become less effective as plants get larger and begin shading the mulch.
There are many natural predators that can help prevent large infestations of cucumber beetles. Spiders, predatory mites, rove beetles, and ground beetles will eat them. A parasitoid fly Celatoria setosa and parasitoid wasp Centistes diabroticae lay their eggs on these beetles. The eggs hatch and larvae infest the beetle leading to mortality.
Nematodes and certain fungi can infect the soil-dwelling larvae of cucumber beetles. Both can be purchased commercially. When applied as a soil drench, they are effective in controlling cucumber beetle larvae.
How To Get Rid Of Striped Cucumber Beetles
If you tried to prevent cucumber beetles but find them feeding on your cucurbits anyways, you’ll want to get rid of them. Using insecticides along with continuing preventative techniques works best for cucumber beetle control.
To protect natural enemy populations when using insecticides, use a trap crop. Trap crops lure insects in so you can apply insecticides to the trap crop rather than the entire garden. Blue Hubbard squash plants work well as trap crops for cucumber beetles. Plant them outside of your garden to lure beetles away, and spray for cucumber beetles using pyrethrin-based insecticides.
Traps may not completely control populations. But they will help you detect when beetles are present so you can begin additional control methods. The best cucumber beetle traps contain a lure and are yellow. There are many different types of cucumber beetle traps available commercially. You can also find traps that also have an insecticide in their lures to provide further control.
How To Get Rid Of Cucumber Beetles Naturally
The best way to get rid of cucumber beetles naturally is by applying natural predators. Such as nematodes or fungi, in a soil drench. Neem oil sprays have also been shown to be effective at controlling cucumber beetles. You can also utilize repellant plants (radish, tansy, and nasturtium), trap crops (Blue Hubbard squash), and reflective mulch to reduce the number of cucumber beetles on cucurbits.
Home Remedies For Cucumber Beetles
There are many home remedies out there that claim to get rid of cucumber beetles. While a direct spray of soapy water or rubbing alcohol may kill these beetles on contact, these methods have not been proven to eliminate entire populations and may damage plants. If you’re interested in using organic management techniques, stick to proven methods. Such as row covers, reflective mulch, repellant companion plants, and natural enemies.
Cucumber Beetle vs Ladybug
Though both cucumber beetles and ladybugs are beetles, there are many differences between the two. Most importantly, cucumber beetles are considered pests in the garden. While ladybugs are predators of many garden pests. The table below covers some of their other differences.
|Genera||Acalymma and Diabrotica||More than 360|
|Adult appearance||Yellow and black coloration with vertical stripes, horizontal stripes, or spots. Long, slender antenna.||Many different colors, and patterns. Short, clubbed antenna.|
|Adult feeding||Herbivores. Flowers, fruits, and leaves of plants. Prefers cucurbits.||Predators (insectivores). Any small, soft-bodied insect it can catch. Prefers aphids.|
|Larva appearance||White, cream-colored, or yellow worm-like body with segments and light to dark brown head capsule.||Generally black with orange or yellow markings and many spines along their back or sides. Body is widest at the head and tapered towards the backend.|
|Larva feeding||Herbivores. Roots and stems of cucurbits.||Predators (insectivores). Any small, soft-bodied insect it can catch. Prefers aphids.|
Frequently Asked Questions
Cucumber beetles are most attracted to cucurbit plants. Such as cucumber, watermelon, pumpkin, and squash. These plants produce cucurbitacin, a chemical that gives them a bitter taste. Any plant that produces cucurbitacin will attract cucumber beetles in search of food.
Cucumber beetles can spread plant diseases such as bacterial wilt (Erwinia tracheiphila) which is typically fatal to plants. They can also transmit Squash mosaic virus which can stunt and distort plants. The feeding damage from cucumber beetle larvae can also make plants more susceptible to fusarium wilt disease.
Cucumber beetles last during the entire cucurbit growing season. Cucumber beetles produce 1 to 3 generations per year. Adults overwinter in leaf litter and emerge in spring. When temperatures are above 60 degrees Fahrenheit. A single beetle that doesn’t overwinter can live for about 8 weeks and females produce over 100 eggs.
Marigolds do not keep cucumber beetles away. Many plants are often used as companion plants in vegetable gardens to reduce pest issues. Some companion plants deter insects. Some increase pest predator populations. And others mask the smells from certain garden vegetable plants. Marigolds work as companion plants by increasing natural enemy populations in your garden.
Cucumber beetles will eat tomato plants if cucurbits aren’t present. While they won’t kill a tomato plant simply by feeding on them, they can transmit bacterial wilt to tomatoes. There is no cure for bacterial wilt and it will ultimately kill the plant.
Cline, G. R., Sedlacek, J. D., Hillman, S. L., Parker, S. K., & Silvernail, A. F. (2008). Organic management of cucumber beetles in watermelon and muskmelon production. HortTechnology, 18(3), 436-444.