Spatial and Temporal Distribution of Geminiviruses in Leafhoppers of the Genus Cicadulina Monitored by Conventional and Quantitative Polymerase Chain Reaction

Spatial and temporal distribution of Maize streak virus (MSV, family Geminiviridae, genus Mastrevirus) was monitored in the vector species Cicadulina mbila and the nonvector species C. chinaï using conventional and real-time quantitative polymerase chain reaction. Sustained feeding on MSV-infected plants showed that virus accumulation reaches a maximum in C. chinaï, but not in C. mbila. After a 3-day acquisition access feeding period (AAP), MSV was detected in the gut, the hemolymph, and the head of C. mbila, but only in the gut of C. chinaï. Similarly, Digitaria streak virus (genus Mastrevirus), which is not transmitted by either of the two species, was only detected in the gut. MSV was detected in the hemolymph of C. mbila 3 h after the beginning of the AAP. Although viral DNA progressively decreases in the vector and nonvector species after a 3-day AAP, MSV DNA remained stable in the salivary glands of C. mbila.

Feeding activities of Cicadulina mbila (Hemiptera: Cicadellidae) on different host-plants

The probing activities of the most important leafhopper vector of maize streak virus, Cicadulina mbila (Naudé) (Hemiptera: Cicadellidae) were studied on different host-plants. Host preference was determined by giving the insects a choice of six plants, Digitaria sanguinalis, Zea mays, Zea perennis, Paspalum conjugatum, Oryza sativa and Saccharum officinarum (all Gramineae). Cicadulina mbila showed a strong preference for D. sanguinalis. Histological examination of plant tissues for salivary sheaths was used to reveal the preferred tissue. Cicadulina mbila tended to ingest from the phloem of its preferred hosts, and switch to mesophyll or xylem tissue on less preferred hosts. The suitability of each host was assessed by measuring the weight gain and amount of honeydew produced on each host by newly emerged adult females. Both parameters were greatest on the preferred host. Probing behaviour was also monitored electronically by recording the different waveform patterns produced when insects were probing, ingesting or not probing on the selected hosts. Cicadulina mbila probed less frequently, ingested longer and spent less time in non-probing activities on its preferred host, D. sanguinalis, although these responses were similar on maize and sugarcane. Rice induced poor probing responses and altered behaviour. This interpretation of the waveforms was supported by histological examination. As maize streak virus (MSV) is not found in phloem sieve elements, prolonged ingestion from sieve cells would not account for efficient acquisition from maize, which would require ingestion from other types of cells. D. sanguinalis was the host in which most ingestion from the phloem occurred, but it is the poorest source of MSV.

Comparative biology of some Cicadulina species and populations from various climatic zones in Nigeria (Hemiptera: Cicadellidae)

Significant differences in nymphal development period and fecundity were observed between five populations of Cicadulina mbila (Naudé) and C. triangula Ruppel from three climatic zones in Nigeria: rain forest (Ibadan), southern part of Sudan savanna (Kadawa, Kano) and the Jos Plateau. The C. triangula population that is used in mass rearing for resistance screening at the International Institute of Tropical Agriculture (IITA), Ibadan, developed much more rapidly than the wild C. triangula population from Ibadan. Similarly, the C. mbila population from the Kadawa Irrigation Scheme, Kano, developed more rapidly than the population from the Jos Plateau. All Cicadulina populations were 3–4 times as prolific on pearl millet as on maize, sorghum or the grass Digitaria exilis. The IITA colony of C. triangula was significantly more fecund than C. mbila. It is clear that Cicadulina species and populations with high reproductive potential would be most suitable for mass rearing for resistance screening to the maize streak virus disease.

Cicadulina mbila. [Distribution map].

A new distribution map is provided for Cicadulina mbila (Naudé) [Hemiptera: Cicadellidae]. Attacks and transmits pathogenic agents to maize, wheat, millet, sugarcane and grasses. Information is given on the geographical distribution in USSR, Tadzhikistan, AFRICA, Angola, Botswana, Cape Verde Islands, Congo, Kenya, Mauritius, Mozambique, Namibia, Nigeria, South Africa, Swaziland, Tanzania, Togo, Uganda, Zambia, Zimbabwe, ASIA, India, Delhi, Himachal, Pradesh, Karnataka, Madhya Pradesh, Mysore, Rajasthan, West Bengal, Yemen.