''Rhopalosiphum maidis'', common names corn leaf aphid and corn aphid, is an

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

, and a pest of

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...

and other crops. It has a nearly worldwide distribution and is typically found in agricultural fields, grasslands, and forest-grassland zones. Among aphids that feed on maize, it is the most commonly encountered and most economically damaging, particularly in tropical and warmer temperate areas. In addition to maize, ''R. maidis'' damages

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

, sorghum, and other cultivated and wild

monocots Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...

Description

The bodies of wingless

parthenogenetic Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...

females are green or whitish-green. The head, antennae, legs,

cornicle The cornicle (or siphuncule) is one of a pair of small upright backward-pointing tubes found on the dorsal side of the 5th or 6th abdominal segments of aphids. They are sometimes mistaken for cerci. They are no more than pores in some species. ...

s, tail, and transverse bands on the abdomen are black-brown. The body has sparse short hairs. The length of the antennae is less than half the length of the body.

Cornicle The cornicle (or siphuncule) is one of a pair of small upright backward-pointing tubes found on the dorsal side of the 5th or 6th abdominal segments of aphids. They are sometimes mistaken for cerci. They are no more than pores in some species. ...

s are not longer than the finger-like tail. In winged females, the head and thoracic section are black-brown and the

s are shorter than in the wingless females. Most ''R. maidis'' populations are anholocyclic, ''i.e.'' reproduction occurs entirely by

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...

. However, sexual reproduction has been reported in

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...

and

Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...

, with ''

Prunus ''Prunus'' is a genus of trees and shrubs, which includes (among many others) the fruits plums, Cherry, cherries, peaches, Peach#Nectarine, nectarines, apricots, and almonds. Native to the North American temperate regions, the neotropics of Sou ...

'' ssp. as the primary host. In populations in Japan and

Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi ...

, males but not sexually reproducing females have been found.

Agricultural interactions

In winter, winged

females and larvae survive on wild-growing

, from which they move to agricultural fields in the spring. Fields populate gradually, starting from the edges to the center. Reproduction is rapid, with up to twelve generations per year. The aphid population reaches a maximum late in the summer. Dense populations of ''R. maidis'' on maize ('' Zea mays'') can cause direct damage through the removal of photosynthates. Large amounts of honeydew that is deposited by aphid feeding on maize tassels can prevent pollen shed and decrease yield by up to 90%. Several damaging maize viruses, including ''Maize yellow dwarf virus'', '' Barley yellow dwarf virus'', '' Sugarcane mosaic virus'', and ''

Cucumber mosaic virus ''Cucumber mosaic virus'' (CMV) is a plant pathogenic virus in the family ''Bromoviridae''. This virus has a worldwide distribution and a very wide host range, having the reputation of the widest host range of any known plant virus. It can be tra ...

'', are transmitted by ''R. maidis''. In addition to feeding on maize, ''R. maidis'' infests a variety of cultivated grasses, including

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley p ...

oat The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other cereals and pseudocereals). While oats are suitable for human con ...

, rye, sorghum, sugarcane, and

. Barley is a particularly suitable host for ''R. maidis'', though there also is considerable within-species variation in resistance.

Chemical ecology

Under enhanced CO₂ conditions, the growth rate and reproduction of ''R. maidis'' on barley were significantly decreased. Volatiles of barley grown under enhanced CO₂ were also less attractive than those from plants grown under atmospheric CO₂. Temperature and crowding have differential effects on wing formation in parthenogenetically reproducing ''R. maidis'' on barley. Maize inbred lines vary in their resistance to ''R. maidis'' and other insect pests. Relative to other maize-feeding aphids ('' Rhopalosiphum padi'', '' Schizaphis graminum'', '' Sitobion avenae'', and '' Metopolophium dirhodum''), ''R. maidis'' exhibits a greater tolerance of benzoxazinoids, the most abundant class of maize defensive metabolites. Nevertheless, lineage-specific variation in maize resistance to ''R. maidis'' was associated with differences in the abundance of 2,4-dihydroxy-7-methoxy-l,4-benzoxazin-3-one glucoside ( DIMBOA-Glc), an abundant maize benzoxazinoid. Both increased DIMBOA-Glc synthesis and reduced conversion to 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA -Glc) can enhance maize seedling resistance to ''R. maidis''. Maize mutations that knock out benzoxazinoid biosynthesis increase ''R. maidis'' reproduction. In some instances, caterpillar feeding can enhance the conversion of DIMBOA-Glc to HDMBOA-Glc, thereby increasing maize resistance against ''R. maidis''. The defense signaling molecules 2-oxo-phytodienoic acid (OPDA) and ethylene are involved in regulating maize resistance to ''R. maidis''. In olfactometer experiments, ''R. maidis'' were repelled by volatiles from damaged maize plants. One of the major volatiles emitted by damaged maize is the terpene (''E'')‐β‐farnesene, which also functions as an alarm pheromone for

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s and thus may be repellent. Mutations of a maize terpene synthase, ''TPS2'', made the plants more attractive for ''R. maidis.''

Genome sequencing

There is within-species variation in the chromosome numbers of ''R. maidis'', with karyotypes of 2n = 8, 9, and 10 having been reported. Whereas ''R. maidis'' strains on maize tend to have 2n = 8, those on barley generally have 2n = 10. To better enable research related to ecological interactions, virus transmission, pesticide resistance, and other aspects of the species biology, a high-quality genome was assembled from a

''R. maidis'' lineage collected from maize. CC-BY_icon

Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. The assembled genome is 321 Mb in size and features a total of 17,629 protein-coding genes. Assembly of the genome was facilitated by the extremely low level of heterozygosity in the sequenced ''R. maidis'' isolate.

Hosts

Barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley p ...

* Millets *

Rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

* Several

Gramineae Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...

species * Sorghums * Sugarcane *

Wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

References

{{Taxonbar, from=Q3703370 Aphidini Agricultural pest insects Insects described in 1856 Taxa named by Asa Fitch Hemiptera of Asia Insect pests of millets