Striped cucumber beetle

The striped cucumber beetle (Acalymma vittatum) is a beetle of the family Chrysomelidae and a serious pest of cucurbit crops in both larval and adult stages.[1] It is replaced in the west by Acalymma trivittatum, a duller species often with greyish or pale white elytra rather than yellow.

Striped cucumber beetle
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Chrysomelidae
Genus: Acalymma
Species:
A. vittatum
Binomial name
Acalymma vittatum
(Fabricius, 1775)

Description

The striped cucumber beetle is a small beetle approximately half a centimeter (1/5 inch) in length, and characterized by brown-yellow elytra completely covering the abdomen and longitudinally transversed by three thick black stripes. It superficially resembles the western corn rootworm (Diabrotica virgifera), another serious crop pest. However, the ventral abdominal surface of A. vittatum is black where that of D. virgifera are yellow, and the elytra of D. virgifera often do not extend the full length of the abdomen.

Life cycle

Large numbers of adults emerge from diapause in the spring to feed on the foliage, flowers, and pollen of cucurbit species. Between one and two generations of beetles can pass in a season depending on the region, with the final generation settling into another period of diapause to wait out the winter.

Females will lay eggs on or in the immediate vicinity of the stem of a viable host plant, often a member of the genus Cucurbita. Eggs are a bright orange color and less than a millimeter in diameter. Eggs hatch after a short period and larvae feed on the roots of the plant.

Agricultural Damage
Feeding damage on a winter squash blossom

Striped cucumber beetles can cause significant amounts of foliar damage to cucurbit crops, particularly to older plants, and larval root feeding also damages the plant. The most damage is often seen in the early part of the year during the emergence of overwintering beetles, but feeding damage continues throughout the entire growing season. Furthermore, adult beetles are one of two known vectors of the bacterial wilt Erwinia tracheiphila, an incurable and often fatal disease of cucurbits. Bacteria passes from the frass of the beetle into feeding wounds that reach into the vascular tissues of the plants, where they proliferate to the point of blocking the xylem.

On Cucurbita sp. flower, Ottawa, Ontario, Canada

Chemical attractants

In Massachusetts, A. vittatum are attracted by several chemicals emitted by cucurbits, including 1,2,4-trimethoxybenzene and indole, though not (E)-cinnamaldehyde.[2] In Illinois, A. vittatum was found to be attracted to indole and (E)-cinnamaldehyde, but not 1,2,4-trimethoxybenzene.[3]

Control Techniques

Grower tolerance for this beetle is very low, due in major part to the transmission of bacterial wilt. Unfortunately, effective control techniques beyond pesticides are few and far between. Research into nematode and other biological control agents continues today. Another possibility is the planting of trap crops (crops that the beetles prefer) around the perimeter of the main crop. The trap crop can then be treated with insecticide, reducing overall pesticide use.[4]

Some research indicates that striped cucumber beetle damage can be reduced by the use of vermicompost fertilizer compared to inorganic fertilizer. Researchers suggest that the mechanism by which vermicompost reduces beetle damage is due to an increase in phenolic compounds in plants grown with vermicompost.[5]

The application of Paecilomyces fumosoroseus to a trap crop is an effective means of controlling the beetle.

Brave new world: recent evolution of an insect-transmitted pathogen a seminar given by Dr. Roberto Kolter

Cucumber beetles and Cucurbitacin

A. vittatum, along with other cucurbit-feeding beetles in the genus Diabrotica, are induced to feeding behavior by a class of plant secondary compounds called cucurbitacins, widespread in members of the family Cucurbitaceae. These extremely bitter chemicals are hypothesized to have evolved as a plant feeding defense, but have been co-opted by the beetles into a kairomonal feeding attractant. Beetles are capable of consuming amounts of cucurbitacins that would kill other organisms, and some work has indicated that the beetle may sequester the compounds in their elytra to deter predation.

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References
  1. Walz, E. (1999), Final Results of the Third Biennial National Organic Farmers’ Survey, Santa Cruz, CA: Organic Farming Research Foundation.
  2. Elizabeth S. Andrews; Nina Theis & Lynn S. Adler. "Pollinator and Herbivore Attraction to Cucurbita Floral Volatiles" (PDF). J Chem Ecol (2007) 33:1682–1691.
  3. Lewis, P. A., Lampman, R. L., and Metcalf, R. L. 1990. Kairomonal attractants for Acalymma vittatum (Coleoptera, Chrysomelidae). Environ. Entomol. 19:8–14.
  4. A. Cavanagh. Hazzard; L. S. Adler & J. Boucher (2009). "Using Trap Crops for Control of Acalymma vittatum (Coleoptera: Chrysomelidae) Reduces Insecticide Use in Butternut Squash". Journal of Economic Entomology. Journal of Economic Entomology 102(3):1101-1107. 2009. 102 (3): 1101. doi:10.1603/029.102.0331. PMID 19610425.
  5. Erdal N. Yardim; Norman Q. Arancon; Clive A. Edwards; Thomas J. Oliver; Robert J. Byrne. "Suppression of tomato hornworm (Manduca quinquemaculata) and cucumber beetles (Acalymma vittatum and Diabotrica undecimpunctata) populations and damage by vermicomposts" (PDF). Pedobiologia 50 (2006) 23—29.
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