Colorado potato beetle
|Colorado potato beetle|
The Colorado potato beetle (Leptinotarsa decemlineata), also known as the Colorado beetle, the ten-striped spearman, the ten-lined potato beetle or the potato bug, is a major pest of potato crops. It is approximately 10 millimetres (0.39 in) long, with a bright yellow/orange body and five bold brown stripes along the length of each of its elytra.
The genus Leptinotarsa is assigned to the chrysolmelid beetle tribe Doryphorini (located in subfamily Chrysomelinae), which it shares with five other genera: Calligrapha, Doryphora, Labidomera, Proseicela, and Zygogramma. This tribe is characterised within the subfamily by round to oval shaped convex bodies which are usually brightly coloured, simple claws which separate at the base, open cavities behind the procoxae, and a variable apicial segment of the maxillary palp.
Adult beetles average 6–11 mm in length and 3 millimetres (0.12 in) in width. The beetles are orange-yellow in colour with ten characteristic black stripes on the elytra. The species name decemlineata, meaning 'ten lines' derives from this feature. Adult beetles may, however, be visually confused with L. juncta, the false potato beetle, which is not an agricultural pest. L. juncta also has alternating black and white strips on its back, but one of the white strips in the center of each wing cover is missing and replaced by a light brown strip.
The orange-pink larvae have a large, nine segmented, abdomen and black head, prominent spiracles and may measure up to 15 millimetres (0.59 in) in length in their final instar stage. The beetle larva has four instar stages. The head remains black throughout these stages, but the pronotum changes colour from black in first- and second-instar larvae to having an orange-brown edge in its third-instar. In fourth-instar larvae, about half the pronotum is coloured light brown.
The beetle is native to America and Mexico and is present in all of the States of America except Alaska, California, Hawaii, and Nevada. It now has a wide distribution across Europe and Asia. Its first association with the potato plant, Solanum tuberosum, was not known until about 1859 when it began destroying potato crops in the region of Omaha, Nebraska. It had spread east and reached the Atlantic Coast by 1874.
In 1877, the Colorado beetle reached the United Kingdom and was first recorded from Liverpool docks. There have been many further outbreaks but the species has been eradicated in the UK at least 163 times. The last major outbreak was in 1976. It remains as a notifiable quarantine pest in the United Kingdom and is monitored by DEFRA in order to prevent it becoming established.
Elsewhere in Europe the beetle became established near USA military bases in Bordeaux during or immediately following World War I and had proceeded to spread by the beginning of World War II to Belgium, the Netherlands and Spain. The population increased dramatically during and immediately following World War II and spread eastward, and the beetle is now found over much of the continent. After World War II, in the Soviet occupation zone of Germany, almost half of all potato fields were infested by the beetle by 1950. In East Germany they were known as Amikäfer ('Yankee beetles') following a governmental claim that the beetles were dropped by American planes. In the EU it remains a regulated (quarantine) pest for the UK, Republic of Ireland, Balearic Islands, Cyprus, Malta and southern parts of Sweden and Finland. It is not established in any of these Member States, but occasional infestations can occur when wind blows adults from Russia to Finland.
Colorado potato beetle females are very prolific; they can lay as many as 800 eggs. The eggs are yellow to orange, and are about 1 millimetre (0.039 in) long. They are usually deposited in batches of about 30 on the underside of host leaves. Development of all life stages depends on temperature. After 4–15 days, the eggs hatch into reddish-brown larvae with humped backs and two rows of dark brown spots on either side. They feed on the leaves of their host plant. Larvae progress through four distinct growth stages (instars). First instars are about 1.50 millimetres (0.059 in) long; the fourth is about 8 millimetres (0.31 in) long. The first through third instars each last about 2–3 days; the fourth, 4–7 days. Upon reaching full size, each fourth instar spends an additional several days as a non-feeding prepupa, which can be recognized by its inactivity and lighter coloration. The prepupae drop to the soil and burrow to a depth of several inches, then pupate. Depending on temperature, light-regime and host quality, the adults may emerge in a few weeks to continue the life cycle, or enter diapause and delay emergence until spring. They then return to their host plant to mate and feed. In some locations, three or more generations may occur each growing season.
Behaviour and ecology
L. decemlineata has a strong association with plants in the family Solanaceae, particularly those of the genus Solanum. They are directly associated with Solanum cornutum (buffalo-bur), Solanum nigrum (black nightshade), Solanum melongena (eggplant or aubergine), Solanum dulcamara (bittersweet nightshade), Solanum luteum (hairy nightshade), Solanum tuberosum (potato), and Solanum elaeagnifolium (silverleaf nightshade). They are also associated with other plants in this family, namely the species Lycopersicon esculentum (tomato) and the genus Capsicum (peppers).
As an agricultural pest
Colorado beetles are a serious pest of potatoes. They may also cause significant damage to tomato and eggplant crops with both adults and larvae feeding on the plant's foliage. Larvae may defoliate potato plants resulting in yield losses of up to 100% if the damage occurs prior to tuber formation.
In about 1840, the species adopted the cultivated potato into its host range and it rapidly became a most destructive pest of potato crops. The large scale use of insecticides in agricultural crops effectively controlled the pest until it became resistant to DDT in 1952 and dieldrin in 1958. Insecticides remains the main method of pest control on commercial farms. However, many chemicals are often unsuccessful when used against this pest because of the beetle's ability to rapidly develop insecticide resistance. Different populations have between them developed resistance to all major classes of insecticide, although not every population is resistant to every chemical. The species as a whole has evolved resistance to 56 different chemical insecticides. Known mechanisms of Colorado potato beetle resistance to insecticides include enhanced metabolism involving esterases, carboxylesterases and monooxygenases, and target site insensitivity, as well as reduced insecticide penetration and increased excretion. There is also some evidence of behavioral resistance.
Bacterial insecticides can be effective if application is targeted towards the vulnerable early-instar larvae. Two strains of the bacterium Bacillus thuringiensis produce toxins which kill the larvae.
Other forms of control, through non-pesticidal management are available. Feeding can be inhibited by applying antifeedants, such as fungicides or products derived from Neem (Azadirachta indica), but these may have negative effects on the plants as well. The steam distillate of fresh leaves and flowers of tansy (Tanacetum vulgare) contains high levels of camphor and umbellulone and these chemicals are strongly repellent to L. decemlineata. Crop rotation may delay the infestation of potatoes and can reduce the build-up of early season beetle populations because the adults emerging from diapause can only disperse to new food sources by walking.
At least thirteen insect genera, three spider families, one phalangid (Opiliones), and one mite have been recorded as predators of the varying stages of L. decemlineata. These include the ground beetle Lebia grandis, the Coccinellid beetles Coleomegilla maculata and Hippodamia convergens, the Shield bugs Perillus bioculatus and Podisus maculiventris, as well as various species of the lacewing genus Chrysopa, the wasp genus Polistes, and the damsel bug genus Nabis.
The predatory ground beetle, L. grandis, is a predator of both the eggs and larvae of L. decemlineata, and its larvae are parasitoids of the pupae. An adult L. grandis may consume up to 23 eggs or 3.3 larvae in a single day.
In a laboratory experiment, Podisus maculiventris was used as a predatory threat to female L. decemlineata specimens, resulting in the production of unviable trophic eggs alongside viable ones; this response to a predator ensured that additional food was available for newly hatched offspring in order to increase their survival rate. The same experiment also demonstrated the cannibalism of unhatched eggs by newly hatched L. decemlineata larvae as an anti-predator response.
Beauveria bassiana (Hyphomycetes) is a pathogenic fungus that infects a wide range of insect species, including the Colorado potato beetle. It has shown to be particularly effective as a biological pesticide for L. decemlineata when used in combination with the bacterium Bacillus thuringiensis.
Relationship to humans
During the Cold War the Warsaw Pact countries, fearing a food shortage, decried the beetle as a CIA plot to destroy the agriculture of the Soviet Union. Officials launched a Warsaw Pact-wide campaign to wipe out the beetle, villainizing them in propaganda posters and pulling schoolchildren from class to gather the bugs and drown them in buckets of benzene or spirit.
2014 pro-Russian conflict in Ukraine
During the 2014 pro-Russian unrest in Ukraine, the word kolorady, from the Ukrainian and Russian term for Colorado beetle, (Ukrainian: жук колорадський, Russian: колорадский жук) gained popularity among Ukrainians as a derogatory term to describe pro-Russian separatists in the Donetsk and Luhansk Oblasts (provinces) of Eastern Ukraine. The nickname was a reference to the black and gold so called St. George's ribbons worn by many of the separatists as a symbol of their identity.
L. decemlineata is an iconic species and has been used as an image on stamps because of its association with the recent history of both North America and Europe. For example, in 1956, Romania issued a set of four stamps calling attention to the campaign against insect pests and it was featured on a 1967 stamp issued in Austria. The beetle also appeared on stamps issued in Benin, Tanzania, the United Arab Emirates, and Mozambique.
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Ukraine’s Reins Weaken as Chaos Spreads, The New York Times (4 May 2014)
(Ukrainian) Lyashko in Lviv poured green, Ukrayinska Pravda (18 June 2014)
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|Wikisource has the text of the 1921 Collier's Encyclopedia article Colorado Beetle.|