''Chilo partellus'', the spotted stalk borer or spotted stem borer,
is a
moth
Moths are a group of insects that includes all members of the order Lepidoptera that are not Butterfly, butterflies. They were previously classified as suborder Heterocera, but the group is Paraphyly, paraphyletic with respect to butterflies (s ...
in the family
Crambidae
Crambidae comprises the grass moth family of lepidopterans. They are variable in appearance, with the nominal subfamily Crambinae (grass moths) taking up closely folded postures on grass stems where they are inconspicuous, while other subfamilies ...
. It was described by
Charles Swinhoe
Colonel Charles Swinhoe (27 August 1838 in CalcuttaAlthough many published sources give 1836, the India Office Records note it as 1838 (), the other year being that of his brother Robert. – 2 December 1923) was an English naturalist and lepido ...
in 1885. It is found in
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
,
Pakistan
Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...
,
Iran
Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
,
Ethiopia
Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...
,
Lesotho
Lesotho, formally the Kingdom of Lesotho and formerly known as Basutoland, is a landlocked country in Southern Africa. Entirely surrounded by South Africa, it is the largest of only three sovereign enclave and exclave, enclaves in the world, t ...
,
Madagascar
Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...
,
Malawi
Malawi, officially the Republic of Malawi, is a landlocked country in Southeastern Africa. It is bordered by Zambia to the west, Tanzania to the north and northeast, and Mozambique to the east, south, and southwest. Malawi spans over and ...
,
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
,
Sudan
Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...
,
Tanzania
Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...
,
Uganda
Uganda, officially the Republic of Uganda, is a landlocked country in East Africa. It is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the ...
and on
Mayotte
Mayotte ( ; , ; , ; , ), officially the Department of Mayotte (), is an Overseas France, overseas Overseas departments and regions of France, department and region and single territorial collectivity of France. It is one of the Overseas departm ...
.
''C. partellus'' is a pest that was introduced to Africa most likely from India in the early 20th century. After arriving in Africa, it has spread to nearly all countries in eastern and southern Africa, and it is assumed that it is spreading to western Africa. ''C. partellus'' is indigenous to Asia and became established in eastern Africa in the early 1930s.
''C. partellus'' is one of the most economically damaging pests in Asia and Africa, attacking all parts of the plant except the roots.
Habitat
''C. partellus'' has rapidly spread over a wide geographical range and has proven to be a very efficient colonizer and devastating pest wherever it may occur. In general, ''C. partellus'' occurs in low to mid-elevations (less than 1500 m) and warmer areas. However, they can now be found in higher elevations such as
Ethiopia
Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...
at 2088 m.
''C. partellus'' is highly invasive and can fully or partially displace other indigenous
stemborer species such as ''
Busseola fusca'' and ''
Chilo orichalcociliellus''. Temperature and humidity can have a significant impact on the survival and establishment of adult ''C. partellus'' in new ecological niches.
Food
''C. partellus'' is a generalist herbivore that feeds on several species of cultivated and wild plants.
Appearance
Eggs are flat and oval and look creamy white and are about 0.8 mm in length.
Larvae of ''C. partellus'' resemble caterpillars and can be creamy white to yellowish brown. These larvae also have four purple-brown longitudinal stripes and are usually found with characteristically dark brown spots along the back, therefore giving off a spotted appearance. When the larvae of the spotted stalk borer are fully grown, they produce a conspicuous reddish-brown head. It has a plate on the dorsal surface of the thorax which is known as a prothoracic shield and is reddish brown to dark brown and shiny.
Pupae can be up to 15 mm in length, slender and shiny. The pupae of ''C. partellus'' are light yellow brown to dark red brown.
Adults are small moths with wing lengths ranging from 7–17 mm and a wingspan of 20–25 mm. The forewings of adults are brown yellowish with darker scale patterns forming longitudinal stripes. The hindwings of males are a pale straw colour and in females the hindwings are white.
Similar species such as ''Chilo orichalcociliellus'' located in East Africa may be confused with ''Chilo partellus''.
Reproduction and life cycle
Eggs are laid in batches of 10–80 on the upperside and underside of leaf surfaces, usually close to the midrib. They hatch after 4–10 days.
Younger larvae (caterpillars) feed on the leaf whorl. Older larvae tunnel into the stems, and it is within these tunnels that they feed and grow for about 2–3 weeks. When these larvae grow completely, they pupate and remain in the stem of the maize. After 1–2 weeks, the adults evolve from the pupae stage and emerge from the stem. They mate and lay eggs on other maize plants and continue to cause damage to the crop.
During dry seasons, larvae may enter a state of
diapause
In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...
or a period suspended development for several months and will pupate once it the dry season is over and there is rain. Adults can emerge from pupae in the late afternoon or early evenings and are active at night. Adults will rest on plants during the day. The whole life cycle takes about 3–4 weeks, however it can vary due to temperature, humidity and other factors. Five or more successive generations may develop in favourable conditions and in regions where there is warm temperatures, high relative humidity, sufficient water and an abundance of host plants. ''C. partellus'' can reproduce and develop all year-round.
Host relationship
This pest causes US$334 million annual loss to sorghum alone in the semiarid tropics.
''C. partellus'' attacks several grass species which can be both cultivated and wild. Cultivated crop hosts include but are not limited to
maize
Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...
,
sorghum
''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a species in the Poaceae, grass genus ''Sorghum (genus), Sorghum'' cultivated for its grain. The grain i ...
,
pearl millet
Pearl millet (''Cenchrus americanus'', commonly known as the synonym ''Pennisetum glaucum'') is the most widely grown type of millet. It has been grown in Africa and the Indian subcontinent since prehistoric times. The center of diversity, and ...
,
rice
Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...
, and
sugarcane
Sugarcane or sugar cane is a species of tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fib ...
. Wild hosts include elephant grass (''
Pennisetum purpureum
''Cenchrus purpureus'', Synonym (taxonomy), synonym ''Pennisetum purpureum'', also known as Napier grass, elephant grass or Uganda grass, is a species of perennial tropical grass native to African grasslands. ''), reeds (''
arrell, G., Simons, S. A., & Hillock ...
''), reeds (''Phragmites'') and vossia (''Vossia cuspidata">Phragmites">arrell, G., Simons, S. A., & Hillock ...