Insect of the Month - Colorado Potato Beetle

  Hort Snacks - July 2017
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 Leptinotarsa decemlineata

Crops Affected: Plants in the Solanaceae (potatoes, tomatoes, eggplant, solanaceous weeds)

Life Cycle:

  • Adults are 10mm by 7mm (1/3 inch by ΒΌ) somewhat rounded beetles with black stripe markings running the length of the back overlaying the pale yellowish colouring
  • Adults overwinter in the soil where crops were previously grown
  • Beetles move upwards as soils warm in the spring – typically emerge in late May or early June
  • Beetles seek out and feed on host plants, starting to mate after several days of feeding
  • Females lay yellow to orange eggs on the underside of leaves in clusters of approximately 30
  • Larvae are humpbacked and reddish-orange with 2 rows of black spots along the side of their body
  • The entire period of egg laying occurs over a couple of months
    • Larvae emerge and feed on the plants for 2-3 weeks until pupating in the soil
  • New adults appear after approximately 3 weeks and feed for a short time before entering the soil for overwintering
  • Typically single generation per season
  • Adults and larval stages feed mainly on the foliage of the plant
  • Irregular holes in leaves and leaf margins – complete defoliation can occur with high populations
  • Some stem feeding may also occur
  • Presence of adults, larvae or eggs in the field
Colorado Potato Beetle larva
CPB Adult
.......................CPB Adult
.....................................................................................................Photos by Brent Elliott

  • Sampling random plants throughout a field, with counts and size estimates of larvae that are present can give some indication of population levels
  • Economic thresholds have not been consistently established; however the presence of 20 large larvae (later instar) per plant may be considered a general threshold for mid-maturing crops (based on a sample of at least 40 plants).
  • Producers should also take into account other crop stress factors and the level of feeding and defoliation that is occurring when determining when to start control measures
  • The use of registered insecticides is a common management practice
    • Care should be taken to rotate between different chemical families, to avoid to build up of resistance (resistant populations have developed to many common chemicals)
    • Use spot treatments to control adults in the early season if possible and systemic larval control products as required (if thresholds are reached)
  • Regular rotations to non-host crops can be an effective tool in keeping populations low and in keeping new populations at the edges of fields
  • Biological controls can be used, however native predators are generally ineffective
  • Control Solanaceous weeds in non-host crops, to make crop rotations more effective
  • In smaller plantings, children can be unleashed with rocks and a jar to collect adults and crush egg clusters and larvae – how effective this is at actually reducing beetle populations is difficult to estimate
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on June 29, 2017.