Does it look as though something has been chewing on the leaves of your cucumber, squash, melon or pumpkins? Are you finding girdled stems and scaring on the fruits? Perhaps you have even noticed that the plants appear smaller this season. If this sounds like your garden then chances are the Striped Cucumber Beetle has come to dine in your garden. 

Striped cucumber beetles (Acalymma vittatum) can be a major pest of cucurbit crops such as squash, melon and cucumbers. The adult cucumber beetles are yellowish in color, about 1/4 inch long, with three black stripes down the length of their abdomen. The thorax is yellowish with no striping while the head and antennae are dark in colour.

Cucumber Beetle Damage

Leaves: The adult beetles chew holes in the leaves and can reduce them to tatters. 
Roots: The larvae feed on the roots which can stunt the growth of the plant. 
Stems: Larvae also feed on stems causing girdling. 
Fruit: Both larvae and adults feed on the fruits causing scaring. 
Disease: Striped cucumber beetles are also vectors for plant diseases like bacterial wilt that can cause the entire plant to quickly wilt then die.

Plants at Risk

Cucumbers, squashes, melons, and pumpkins are the preferred food choices of the striped cucumber beetle but they will also feed on tomatoes and other garden crops if cucurbits are unavailable or there are more beetles than the available cucurbits can support.

Life Cycle

Adult beetles overwinter in plant debris and emerge in mid-spring, when temperatures reach about 18 degrees C. (right about the time cucurbit seedlings are beginning to emerge through the soil). Planting transplants rather than seeds may help give your plants a head start and get them past this vulnerable period. According to William F. Lyon and Alan Smith of the Ohio State University Extension Entomology the beetles will soon mate and the females will deposit 225-800 eggs in small clusters or singly into soil cracks at the base of cucurbit plants. This is said to occur about 8-25 days after mating, with the eggs hatching 5-8 days later. The larvae then spend about 15 days feeding on the roots and stems of fruit that is in contact with the soil. The time from egg to adult for the first generation of beetles requires about 1 month. Southern Ontario  has only one generation per year.

Control

Cultural Practices

• Hand picking
• Crop rotation: The Striped cucumber beetle lays it’s eggs in the soil at the base of the plant. Planting your cucumbers in a different location the following year will help to reduce populations.
• Clean up all plant debris as the beetles over winter in the plant debris.
• Row covers (remove during flowering period).
• Attract natural predators to your yard like tachinid flies, soldier beetles, braconid wasps, ladybugs, green lacewing and assassin bugs, which will all feed on various life stages of cucumber beetles. 

Sprays

• Apply kaolin clay (Surround WP) to plant foliage. The film left behind disorients insects and prevents feeding. ARBICO Organics (n.d.)). (only available commercially in Canada).
• Spinosad sprays can be applied as soil drenches to kill larvae before they pupate in the soil (ARBICO Organics (n.d.)). (Spinosad is currently under review in Canada).
• Monterey Fruit Tree & Vegetable Systemic Soil Drench (currently under review in Canada).
• NemaSeek (Hb) beneficial nematodes are applied to the soil of infested areas to control the pupal stage of the cucumber beetle(ARBICO Organics (n.d.)).

Cucumber Beetles Vectors of Other Diseases

The cucumber plant picture above will have to be destroyed. It has been infected with the Bacterium – Erwinia tracheiphila, causing what is referred to as Cucumber Wilt or Bacterial Wilt. The bacterium overwinters in the bodies of hibernating cucumber beetles who then introduce the bacteria into the plants through the fecal contamination of feeding wounds. The disease appears first as patches of discoloration, followed by a sudden wilting of the plant. The wilting damage to the cucumber plant pictured above occurred in the space of 2-3 days. The beetles are also known to spread squash mosaic virus. All cucurbits, except watermelon are potentially affected by the disease.

Photo credits: all photos have been taken by the author.

References:

ARBICO Organics (n.d.) Cucumber Beetle How To Control Cucumber Beetles Using IPM. https://www.arbico-organics.com/category/cucumber-beetle-control

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