Colorado Potato Beetle
- Looking to know more about the Colorado potato beetle? Whether you learned about them out of curiosity or while researching insecticides, you’ll find the information here useful.
Leptinotarsa decemlineata is an important pest in the Chrysomelidae family. The L.decemlineata is a serious threat to many plants of the Solanaceae family, especially the genus Solanum. It’s known to cause damage to the pepper and potato crops and can develop resistance to insecticides easily. This pest spread throughout the world from America after the Second World War. The Colorado potato beetle is believed to have originated in America.
At times, there is confusion between male Colorado potato beetles and “False potato beetles.” This is mainly because both have alternating black and white stripes on their backs. The Colorado potato beetle has several nicknames, such as the “ten stripped spearmen,” “ten-lined potato beetle,” and “potato bug.” It is about 10 mm long, with brown stripes.
Nomenclature and taxonomy
Leptinotarsa decemlineata is a member of the genus Leptinotarsa in Chrysomelidae family of order Coleoptera. More than 40 species of Leptinotarsa are found throughout the north of Mexico. A complete list of the synonyms of L. decemilneata has been provided by Jacques in 1988.
This genus contains two subspecies:
- Colorado potato beetle (Leptinotarsa decemlineata)
- False potato beetle (Leptinotarsa juncta)
The size of an adult beetle is about 3/8 inch long. They generally appear as yellowish-orange with black stripes on the backs. They are oval-shaped when seen from above. There are irregular dark markings on the thorax and the head possesses a triangular black spot. The black spot on the outer margin of the femur and orangish color of legs is a distinct feature of L. decemlineata among other members of the Chrysomelidae family.
- Potato beetle eggs vary from 1 to 1.5mm long.
- The eggs are yellow in color and oval-shaped.
- Generally, the beetle lays eggs in a group of 12-25 on the underside of potato leaves.
- The beetle possesses ten characteristic black strips on the elytra: the name of species decemlineata, meaning 'ten-lined', is derived from this feature.
Availability, Distribution, and Habitat
In 1811, Thomas Nuttall first discovered this beetle in Florida. However, it was only properly described in 1824 by American entomologist Thomas Say. This insect’s affinity for potato plants was established in 1859. Significantly notable was their attack on potato plants starting from Nebraska of the U.S.A. After damaging potato crops in America, the potato beetle spread to the Atlantic coast.
After some time it had successfully established itself in Europe, too. Colorado potato beetles are reported on the islands of Jersey, as well as Spain, Norway, Denmark and many countries in Asia. However, some parts of America such as Alaska, California, Hawaii, and Nevada are free from the Colorado potato beetle.
The Colorado potato beetles are found in a large number of crops that belong to the Solanaceae family, particularly potatoes and aubergines. The adults of this beetle feed on the tubers of the host plant, as well as on leaves and other growing parts such as the stem. The false potato beetle is confined to some eastern parts of the U.S.A.
The beetle's diapause can be found at the depth of 7.6 to 12.6 cm in the soil. These adults emerge from the soil in favorable conditions, such as in the early summer or spring season. The suitable temperature for the development of Colorado potato beetle is 25°C, and the temperature at the time of egg-laying should be between 15-30°C. The process of egg-laying continues for several weeks, and a female can lay up to 2000 eggs. The larvae hatch from the egg after 14 days with the help of their oviraptors, which are situated on the mesothorax and metathorax segments.
The colorado potato beetle goes through 4 total instars, the last stage being larval or pupal. For proper larval development, a temperature of 14 to 29°C is suitable. Temperature below 8-13°C suspends the activity of larval development and mortality occurs quickly. Sometimes, cannibalism is observed (particularly during the first instars) at high temperatures and low humidity.
The female beetle deposits eggs in groups under potato leaves so that they’re protected from direct sunlight. An adult female takes 4 to 5 weeks for the deposition of 300 eggs. An egg can hatch in 10 to 14 days, depending on environmental conditions. The period of all instars is 21 days. The larvae stops feeding on leaves after molting, then drop from the plant and transform into a yellowish pupa of spherical shape.
It takes around 5-10 days for the completion of this stage. Generally, there is no difference between the life cycles of false potato beetles and Colorado potato beetles. In false potato beetles, it takes 4-5 days to hatch the eggs, and after hatching the larvae feed on leaves of plants. After the completion of all stages, larvae fall from the plant and pupate for 10-15 days, depending on climatic conditions such as humidity and temperature.
The colorado potato beetle has various natural predators. It has been identified that three spider families, one phalangida, and one mite are specialized predators of L. decemlineata. The green lacewings, many stink bugs, and spined soldier bugs are the main natural enemies of Colorado potato beetle. Among parasitoid, a tachinid fly named Myiopharus doryphorae which becomes numerous in autumn is another important enemy. Generally, this tachinid fly affects the last generation of Colorado beetle. So, predators play a key role in controlling the population of these serious pests of potatoes and other related crops.
Biological Pest Control Management
This beetle feeds on leaves and causes great damage to potato, eggplant, and pepper crop. The problem in controlling this beetle is that it develops resistance to many pesticides. So, it is necessary to change pesticide according to the level of incidence, climatic conditions, and crop variety.
Bacillus thuringiensis var. tenebrionis (Bt) is effective against larvae. Generally, pesticides are not recommended if there are only one to two larvae per leaf. Some natural enemies of this beetle such as birds, predatory stink bugs, and parasitic flies help to reduce the damage caused by the Colorado beetle. Hand-picking is also an effective method for controlling the beetle.
Note: One must read and follow label directions for safe and effective use of any pesticide!