Leptinotarsa decemlineata

(Colorado potato beetle)

General  

• Beetle insect native to Central America, found all over the world. Very damaging in hot weather, favoring the succession of several generations of the insect during the season.
• Heavy infestations of larvae cause severe defoliations which can reduce yields to a greater or lesser extent.
• Grows mainly on potatoes but can also affect other cultivated or wild Solanaceae (eggplants, tomatoes ...).
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Biology

• Development cycle:
  • The adult lays yellow-orange eggs in clusters on the underside of the leaves.
  • The larva, slightly curved and red-orange in color, has a double row of black spots on the side of the abdomen.
  • At the end of the last generation in the field, the larvae enter the soil of the potato plots or the environment and develop into pupae and later into adults which can overwinter in the soil.
  • The adult is about 10 to 12 mm long and has a rather rounded appearance. Its anterior part (head and thorax) has an orange-yellow color with several black dots and the two hardened wings (elytra) are pale yellow in color with five black stripes on each elytron.
• The length of their cycles is variable and depends on the temperature: one month in hot summers, 2 to 3 months if conditions are not optimal, one to four generations can be formed each year.
• The adults overwinter in the soil (20 to 30 cm) and ascend in late spring to consume the first potato shoots and sometimes even the epidermis of the stems.
• The larvae begin to devour the leaves which bear them and then migrate to the top of the plant devouring large proportions of the leaf blade.
• The climate is the factor which most conditions the development of the Colorado beetle (in particular the temperature), before the impact of high populations of insects in the environment the previous year and the presence of host plants.

Protection

• In affected open-field plots, carry out crop rotations, in particular with cereals (reducing insect migrations).
• Avoid planting eggplant crops near old or potato crops.
• Destroy potato regrowth and weeds (especially black nightshade) at the end of winter.
• Avoid working the soil when the larvae are trying to enter it (summer), which would facilitate their burial;
• Several insecticides are effective on the Colorado potato beetle:
  • Above all, alternate families of insecticides in order to limit the risks of resistance as much as possible;
  • Prefer early treatments on young larvae which are much more sensitive than the other stages of development;
  • Note that several insecticides authorized against aphids are also effective against the Colorado beetle, particularly on young larvae.
• Biological insecticides, in particular based on Bacillus thurigiensis, are authorized in certain countries for the control of the Colorado beetle in potato crops;