Chilo Partellus
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''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 ...
,
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,
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 ...
,
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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 ...
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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 ...
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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. arrell, G., Simons, S. A., & Hillock ...
''), reeds (''Phragmites'') and vossia (''Vossia cuspidata">Phragmites">arrell, G., Simons, S. A., & Hillock ...
''), reeds (''Phragmites'') and vossia (''Vossia cuspidata''). In nature, an insect locates a host plant through a sequence of behavioural and biological responses such as the following: #Orientation and setting #Feeding #Metabolism of ingested food #Growth #Survival and fecundity #Oviposition If one or more of these categories of insect responses are not met by the host plant, the plant would therefore be rendered as unsuitable or unfavourable for insect establishment. Therefore, the extent of insect establishment depends on the interaction of insect responses to various plant characteristics. Numerous factors can enhance the insect pest problem, this includes either manipulating the environment that are favourable for growth, reproduction and development of insects. Processes that could decrease the insect pest problem include unrestricted use of chemicals (insecticides) and imbalanced use of fertilizers. Infestation can start around two weeks after seedling emergence. The first symptom of damage is the presence of irregular shaped pinholes or shot holes caused by early-instar larval feeding in the whorl. This can later convert to elongated lesions on the leaves. The infested plants appear ragged and deteriorated. The older larvae leave the whorl, break through and bore into the stem and reach the growing point. It is there that the larvae cut and cause the characteristic deadheart symptom. Therefore, the damage due to the pest includes leaf feeding and subsequent destruction, extensive tunnels in stems and maize cobs, disruption in the nutrient flow, and the resultant death of the plant due to the puncture of the growing point.


Host defences

Studies have shown that some host plants to ''C. partellus'' have developed defences and therefore resistance to this pest. For example, some maize
landrace A landrace is a Domestication, domesticated, locally adapted, often traditional variety of a species of animal or plant that has developed over time, through adaptation to its natural and cultural Environment (biophysical), environment of agric ...
s have been shown to respond to early herbivory (e.g. egg deposition) by ''C. partellus'' by producing herbivore-induced plant volatiles (HIPVs) which would attract parasitoids of ''C. partellus''. It is assumed that this is an opportunity for the exploitation of this trait and can be used as management of this pest. However, this particular defensive technique requires further study for it have very little to no information available regarding other factors including host plant defences on larval preference and development, ''C. partellus'' oviposition behaviour after HIPV production, etc. Also, host plants may have created a defence where leaf feeding by ''C. partellus'' may have induced secondary defence metabolites making plants unpalatable. Therefore, this could represent another opportunity for the management of ''C. partellus''.


Pest management and biocontrol methods

There are a few methods that could be used in order to reduce the pest population of ''C. partellus''. Methods and processes include but are not limited to the following: Detection methods: Infestations by ''C. partellus'' can be detected by walking through crops looking for the characteristic physical appearance of a deteriorated host plant by the presence of deadhearts. Samples of infested stems can be cut open to find caterpillars and pupae, however it is a good idea to rear these until adulthood to be certain that they are ''C. partellus'' pests. Cultural practices:
Intercropping Intercropping is a multiple cropping practice that involves the cultivation of two or more crops simultaneously on the same field, a form of polyculture. The most common goal of intercropping is to produce a greater yield on a given piece of land ...
or mixing maize with non-host crops like
cassava ''Manihot esculenta'', common name, commonly called cassava, manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America, from Brazil, Paraguay and parts of the Andes. Although ...
can reduce the population of ''C. partellus''. Trap plants such as Napier 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. push-pull". Also, marking sure to destroy all residue of infested maize to ensure the death of all larvae would decrease the chances of reinfestation. Biological control: Two parasitic wasps (''Cotesia flavipes'') and (''Xanthopimpla stemmator'') can attack and kill ''C. partellus'' pests. These parasitic wasps can lay eggs into ''C. partellus'' (''C. flavipes'' on adult and ''X. stemmator'' on the pupae) and upon hatching, these eggs feed internally into the pest. They then exit and spin cocoons. Therefore, management of habitats that conserve these parasitic wasps could also result in the decline of ''C. partellus'' populations. Chemical control: Applications of granules or dust to the leaf whorl early in crop growth could kill early larval instars. However this has limited effectiveness, especially once the larvae has bored into the stem. Also, studies indicate that
nitrogen fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...
can be applied as an integrated pest management tactic in control of ''C. partellus'' population development and infestation on maize crop.


Human impact

Climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
could be one of the possible reasons this pest is moving to higher altitudes and therefore increasing its geographic range. This is due to a study showing that temperature, relative humidity, and interaction significantly affect the developmental time of ''C. partellus''. A study found that the egg period was longer at lower temperatures for ''C. partellus'', therefore there is a reduction in larval period with an increase in temperature due to increased metabolic activity and feeding. Also, the pupal period was shorter at higher temperatures, therefore higher temperatures have a significantly shorter egg to adult developmental period. Egg hatching was faster at higher relative humidity, therefore this study and its results imply that high relative humidity modifies the effect of temperature and contributes to the variation in the egg period of ''C. partellus''. In addition, higher temperatures also indicated a reduction in the length of their life cycle, a reduced developmental time and an increase in developmental rates. Therefore, the duration of adult longevity of this pest is inversely related to temperature.Tamiru, A., Getu, E., Jembere, B., & Bruce, T. (2012). Effect of temperature and relative humidity on the development and fecundity of ''Chilo partellus'' (Swinhoe) (Lepidoptera: Crambidae). ''Bulletin of Entomological Research'', 102(01), 9-15.
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References

{{Taxonbar , from=Q2188710 Chiloini Moths described in 1885 Agricultural pest insects Insect pests of millets Moths of Sub-Saharan Africa Moths of Asia Moths of Madagascar Moths of the Comoros