Cicadulina mbila (Naudé 1924a: 307 )Membracoidea : Cicadellidae
|Diseases Transmitted||Pathogen Type|
|Crops Affected by Cicadulina mbila (Naudé 1924a: 307 )|
This species is a vector of two races, “A” and “B,” of maize streak virus, Uba cane streak virus; and maize mottle virus. Storey in 1924 (766) was first to report transmission of maize streak virus by this species under the name “Balclutha sp.” Complete details of transmission were given later by Storey in 1925 and 1928 (767, 769). Transmission under the name “Balclutha mbila” was initially done in cage experiments by collecting leafhoppers from diseased maize and transferring them directly to healthy caged plants. Most of the plants became diseased in 14 days after the insects fed on them. In greenhouse tests, transmission was effected to 46 plants by individuals that had previously been collected from diseased maize fields. Additional testing showed that some individuals never transmitted the Virus.
Previously noninfected leafhoppers were fed on diseased plants for 1 week and transferred to healthy plants for 7 days. Of 62 leafhoppers tested, 37 acquired the virus. Transmission of the virus by all instars was demonstrated (Storey 1928) . The infectivity of nymphs after molting was not lost, even to the adult stage. The insect was able to pass the virus after 1 hour of feeding on diseased plants. A higher percentage of females than males were infective after being reared from egg to adult on diseased plants. Adults were able to remain infective until death. One individual lived 150 days and transmitted the virus during the last 10 days of its life. The incubation period of the virus in the insect was between 12 and 48 hours at 30° to 35° C. The minimum period varied between 6 and 12 hours at 30°.
While testing single insects versus groups of 12 leafhoppers, a higher percentage of transmission occurred with groups of insects. Single leafhoppers infected 7 of 24 plants whereas the group infected 23 of 24 plants.
Storey in 1926 (768) demonstrated transmission of a virus from sugar-cane to sugarcane and he later determined it as a distinct strain from maize streak virus. Detailed transmission experiments were carried out by Storey and McClean in 1930 (775), in which the virus was transmitted to maize, Uba cane, and several species of grasses. Maize streak virus was transmitted to Uba cane but the infections were not permanent. Transmission of a virus from Uba cane to Uba cane was effected easily but only caused a mild form of streak disease when transmitted back to maize. The virus was transmitted to two species of grasses and caused differences in severity when transmitted back to maize or Uba cane. Evidently different strains of the maize streak virus were involved as evidenced by symptoms produced in the host plants.
Storey in 1932 (771) bred pure active races of this species, which always transmitted the virus, and a pure inactive race, which never transmitted maize streak. The inheritance involved was a simple dominant factor linked with sex. Active males crossed with inactive females produced F1 progeny of inactive males and active females. In the F2, active and inactive forms appeared in equal numbers in each sex. In reciprocal crosses, inactive males crossed with active females gave active and inactive males in equal numbers and only active females.
Individuals of the inactive race were made infective by injecting infective juice by needle into the insect’s body. This led Storey in 1933 (772) to conclude that virus particles must pass through the gut wall into the blood, where it is carried to the salivary glands.
Transmission of maize mottle virus was first reported by Storey in 1937 (774). Using the uninfected active race he transmitted the virus to maize seedlings by feeding 20 individuals on infected maize. All plants used in the tests were infected. None of the individuals from the inactive race transmitted the virus. Individuals transmitted both viruses of maize streak and maize mottle simultaneously and successively.
The distinction between “A” and “B” forms of the maize streak virus was first reported by McClean in 1947 (504). The “A” form was the same virus used in nearly all of Storey’s work whereas the “B” form and other types were distinguished as new strains of maize streak virus. These forms as well as the Uba cane virus were differentiated by host reaction and incubation period of the virus in the host. These isolates were transmitted by mbila, which caused either transitory or permanent infections depending on the host.
This species is considered the most important vector of these viruses in Africa.
Small, fragile species. Length of male 2.80—3.00 mm., female 2.90—3.10 mm.
General color yellow and black. Crown yellow with two distinct round spots on anterior margin; pronotum yellow, lateral angles suffused with black; scutellum yellow; elytra with longitudinal blackish band on lateral half and yellowish-white band on each side of commissure.
Pygofer in lateral aspect about as long as wide, long process arising from caudodorsal margin and projecting ventrad, apex of process forked; aedeagus in lateral aspect simple, tubelike, with two small processes on ventral margin; gonopore terminal; style in dorsal aspect simple, apides very broad, short, with lateral tooth; female seventh sternum in ventral aspect with caudal margin excavated, median protuberance on middle (fig. 65).
From latens, to which it is similar in genital characteristics, mbila can be separated by the pygofer processes with the apex having a short apical and long subapical projections.
|Nielson, M. W. 1968b. The leafhopper vectors of phytopathogenic viruses (Homoptera, Cicadellidae). Taxonomy, biology and virus transmission. United States Department of Agriculture Technical Bulletin . 1382 386 pp.|