Cucumber Beetle Life Cycle: A Quick Guide for Gardeners

Cucumber beetles are a common pest that can cause significant damage to various plants, particularly cucurbits like cucumbers, squash, and melons. There are two main types of cucumber beetles: the striped cucumber beetle (Acalymma vittatum) and the spotted cucumber beetle (Diabrotica undecimpunctata).

The life cycle of cucumber beetles is an important aspect to understand, as it can help with management and control strategies. Both types of beetles have similar life cycles, which involve four stages: egg, larva, pupa, and adult. Eggs are typically laid in the soil at the base of the host plants, and larvae emerge to feed on the roots and underground parts of the stems. After a period of feeding, the larvae pupate in the soil before emerging as adults.

During the adult stage, cucumber beetles can directly damage plants by feeding on foliage, flowers, and fruit, while also transmitting bacterial wilt and other plant diseases. By understanding the life cycle and various stages of these pests, gardeners and farmers can better plan preventative measures and take action to mitigate the damage they cause. For example, planting cucurbits later in the season can help avoid early season infection with bacterial wilt, as older plants are less susceptible to the disease (*).

Cucumber Beetle Overview

Striped Cucumber Beetle

The Striped Cucumber Beetle (Acalymma vittatum) is a common pest of cucurbits, which include cucumbers, pumpkins, and squash. They have black stripes on their wing covers and are known to transmit mosaic virus in these plants. Adult beetles lay their eggs in the soil, which hatch in 14 to 21 days1. Larvae feed on roots and underground parts of stems for two to three weeks before pupating in the soil1.

  • Size: Small
  • Color: Yellow with three longitudinal black stripes2
  • Host plants: Cucumber, pumpkin, squash, and other cucurbits
  • Disease transmission: Mosaic virus

Spotted Cucumber Beetle

The Spotted Cucumber Beetle (Diabrotica undecimpunctata howardi) is another leaf beetle pest affecting cucurbits like watermelon. Unlike the striped variety, the spotted cucumber beetle has 12 black spots on its wing covers3. Their life cycle is similar to that of the striped cucumber beetle. They lay eggs in the soil, and their larvae feed on roots and underground stems.3

  • Size: Small
  • Color: Yellow with 12 black spots on wing covers3
  • Host plants: Watermelon, cucumber, and other cucurbits
  • Disease transmission: Mosaic virus
Feature Striped Cucumber Beetle Spotted Cucumber Beetle
Color Yellow with black stripes Yellow with black spots
Host plants Cucumber, pumpkin, squash Watermelon, cucumber
Disease transmission Mosaic virus Mosaic virus

Life Cycle and Biology

Eggs

Cucumber beetle eggs are pale orange-yellow and are laid in groups by the adult beetles. The striped cucumber beetle deposits eggs around the base of plants, on vines, or just below the soil surface, whereas the spotted cucumber beetle prefers to deposit eggs in wet, coarse soil.

Larvae

The larvae of both species are small (3/8 in) and creamy white in color. They hatch in 14 to 21 days and feed on roots and underground parts of stems. Larvae are one of the most destructive stages of the cucumber beetle life cycle.

Pupal Stage

After two to three weeks of feeding, the larvae pupate in the soil. This is a transitional stage between larvae and adult beetles. Pupation lasts for about one week.

Adult Beetles

Adult striped and spotted cucumber beetles are similar in size and shape. The adult striped cucumber beetle has black and yellow stripes, while the spotted cucumber beetle has 12 black spots on its wing covers. The adults emerge from pupation in mid- to late May. Once emerged, they feed on cucurbit plants, such as cucumbers, melons, and squash.

Comparison between Striped and Spotted Cucumber Beetles:

Aspect Striped Cucumber Beetle Spotted Cucumber Beetle
Coloring Black and yellow stripes 12 black spots on wing covers
Egg-Laying Location Around plants, on vines, or just below soil surface In wet, coarse soil
Season Overwinter; emerge in mid- to late May Migrate to northern areas

Only striped cucumber beetles overwinter in areas like Wisconsin, while spotted cucumber beetles migrate to northern areas. Both species can cause significant damage to cucurbit plants.

Damage and Impact

Feeding Damage

Cucumber beetles cause damage to cucurbit plants by feeding on leaves, flowers, and fruits. Their feeding can result in:

  • Defoliation
  • Scarring of fruits
  • Reduced plant vigor

For example, the striped cucumber beetle feeds on cucurbits like cucumbers, summer and winter squashes, melons, and pumpkins.

Bacterial Wilt

Cucumber beetles can transmit a disease called bacterial wilt, which is caused by the bacterium Erwinia tracheiphila. The symptoms of bacterial wilt include:

  • Wilting of leaves
  • Yellowing of foliage
  • Premature death of plants

Bacterial wilt primarily affects young cucurbit plants at the cotyledon and 1-4 leaf stage.

Mosaic Virus

Cucumber beetles are vectors for mosaic viruses like:

  • Squash mosaic virus
  • Cucumber mosaic virus

These viruses can cause a variety of symptoms, including:

  • Mottled, yellow leaves
  • Stunted plant growth
  • Reduced fruit production
Feeding Damage Bacterial Wilt Mosaic Virus
Symptoms Defoliation Wilting of leaves Mottled, yellow leaves
Scarring of fruits Yellowing of foliage Stunted plant growth
Reduced plant vigor Premature death of plants Reduced fruit production

Prevention and Control

Cultural Controls

  • Planting time: Delay planting until late May, when cucumber beetles are less active.
  • Trap crops: Plant perimeter trap crops like squash or gourds to lure beetles away from main crops.
  • Host plants: Remove other host plants, such as wild cucurbits, from the vicinity.
  • Garden debris: Dispose of garden debris and compost piles regularly to prevent overwintering.

Cultural control methods involve focusing on changing the environment to make it less conducive for cucumber beetles. For example, planting crops during late May can help reduce beetle infestations, as they are less active during that time. Additionally, using trap crops and removing host plants can also help.

Physical Controls

  • Floating row covers: Use floating row covers or hoops to keep beetles off young transplants.
  • Monitoring: Regularly check for signs of cucumber beetles and take appropriate action.
  • Mulch: Apply a layer of mulch to suppress adults from laying eggs.

Physical controls help prevent cucumber beetles by creating a barrier or making the environment less hospitable. Examples include using floating row covers to protect plants and applying mulch to deter the beetles from laying eggs.

Chemical Controls

  • Systemic insecticides: Treat the plant’s vascular system to protect against beetles.
  • Foliar insecticides: Apply insecticides to the plant’s foliage.
  • For transplants: Use insecticides when planting transplants, following the New England Vegetable Management Guide.

Chemical controls involve using insecticides to kill or deter cucumber beetles. This includes treating plants with both systemic and foliar insecticides, as well as using insecticides during transplanting according to the New England Vegetable Management Guide.

Treatment Method Pros Cons
Systemic Protects plant’s vascular system May harm beneficial insects
Foliar Targets visible beetles Requires frequent reapplication

Biological Controls

  • Beneficial insects: Encourage ladybugs and lacewings as natural predators.
  • Thresholds: Monitor beetle populations and apply control measures when they reach a predetermined threshold.

Biological controls involve using living organisms, like beneficial insects, to control pest populations. Encouraging the presence of ladybugs and lacewings can help as they prey on cucumber beetles. Monitoring beetle populations and applying control measures when they reach a certain threshold can also help manage infestations.

Identification and Monitoring

Visual Inspection

Monitoring cucumber beetles, both striped and spotted, can be done through regular visual inspections during the growing season, starting in early June. Focus on checking young plants and field edges, as beetles are often found feeding on leaves and stems. Striped cucumber beetles have distinctive yellow and black stripes, while the adult spotted cucumber beetle has 12 black spots on its wing covers.

Be on the lookout for creamy white larvae of both species feeding on plant roots during the pupal stage. Additionally, watch for signs of wilting, which may indicate an infestation.

Yellow Sticky Traps

Another monitoring method for cucumber beetles is using yellow sticky traps. These traps attract the beetles and catch them, making it easier to assess their abundance in your garden or field. Place traps close to the ground, near young plants.

Pros:

  • Simple to set up
  • Effective for catching beetles

Cons:

  • May also catch beneficial insects
  • Requires regular trap maintenance

Here’s a comparison between striped and spotted cucumber beetles:

Characteristic Striped Cucumber Beetle Spotted Cucumber Beetle
Pattern Yellow with black stripes Yellow with 12 black spots
Overwintering As adults in soil or plant debris As adults in wooded areas or plant debris
Preferred feeding stage Young plants, cotyledon and 1-4 leaf stage All plant stages
Main concern Wilt transmission in immature plants General feeding damage

Once cucumber beetles are identified and monitored, implement appropriate control measures for both striped and spotted beetles, such as crop rotation, resistant varieties, and targeted insecticides in case of severe infestation.

Footnotes

  1. Wisconsin Horticulture 2

  2. Clemson University

  3. UMN Extension 2 3

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Banded Cucumber Beetle

 

Please help identify spectacular picture
Hi,
I recently took this photo at a local nursery where I was photographing different flowers. This bug was so colorful and cute, I justhad to snap some pics of it. But I’m having trouble identifying it. Can you help? I live in Southern California near the ocean. Thanks,
Jessica Straw

Hi Jessica,
What a gorgeous image of a Banded Cucumber Beetle, Diabrotica balteata. According to BugGuide: “Larva eat roots, and adults eat the rest of the plant parts.”

Letter 2 – Banded Cucumber Beetle from Argentina, we think

 

Consulta desde Argentina
Hola
Lamento no escribir en inglés, puesto que soy malo para ese idioma. Quisiera saber qué es el bicho que les adjunto. La fotografía la tomé en la ciudad de Gualeguay , Argentina El insecto (de aproximadamente unos 5 mm de largo, si no recuerdo mal) está posado sobre el pétalo de una rosa. Excelente página!! Saludos. Muchas gracias
Ariel

Hola Ariel,
Perdon, porque nuestro Espa

Letter 3 – Banded Cucumber Beetle from Mexico

 

What bug is this?
Location: Santiago de Queretaro, Mexico.
September 11, 2011 11:52 pm
September 7th 2011
Can you tell me what bug is this?
It just flew right at me.
It was around 10 pm kind of chill outside. Luckly I had my camera next to me.
Regards,
Frank J Morales Pizana
Signature: Frank

Banded Cucumber Beetle

Hi Frank,
This Banded Cucumber Beetle is one of the Leaf Beetles, and according to BugGuide:  “Larva eat roots, and adults eat the rest of the plant parts” presumable of cucumbers and related plants.

Letter 4 – Spotted Cucumber Beetle

 

Yellow beetle with black spots
Location:  Torrington, CT
October 18, 2010 5:21 pm
Hi there! I’m constantly scanning my outdoor plants for bugs I’ve never seen. I see something new almost every day! I came across this pretty little beetle in the center of a small sunflower. Can you tell me about it? Thanks!
Signature:  Jennifer

Spotted Cucumber Beetle

Dear Jennifer,
Your beetle is a Spotted Cucumber Beetle,
Diabrotica undecimpunctata, and according to BugGuide, the larva is known as the Southern Corn Rootworm.  BugGuide also contains this comment:  “Considered a major pest of many field crops including cucumbers and other squashes, corn, soy. Beetles also transmit crop diseases such as bacterial wilt. Adults also reported damaging to garden plants including hibiscus, roses.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

    View all posts
  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

    View all posts

1 thought on “Cucumber Beetle Life Cycle: A Quick Guide for Gardeners”

Leave a Comment