Stylet penetration behaviours of four Cicadulina leafhoppers on healthy and maize streak virus infected maize seedlings.
Cicadulina leafhoppers (Homoptera: Cicadellidae) are major pests of maize (Zea mays L. (Poacea) as they transmit maize streak virus (MSV), the most important virus of maize in Africa. The stylet penetration behaviours of four species (C. arachidis, C. dabrowskii, C. mbila and C. storeyi) were studied with an alternating current (AC) electrical penetration graph (EPG) monitor to understanding how feeding differs among the species that have different transmission efficiencies on healthy and streak-infected maize seedlings. The stylet penetration behaviours were significantly affected by the infection status of the host plants in six out of eight measured response variables. The vectors preferred feeding on healthy plants, to streak-infected plants as the insects spent more time on non-probing behaviours like resting or walking when on streak-infected hosts than on healthy plants. There were more pathway activities (salivation and searching for phloem cells) and frequency of probing was higher when feeding on streak-infected seedlings. This might indicate the times that the virus is picked up from infective tissues. Feeding from phloem cells, overall probing and probe mean (the average time per probe) were higher on healthy than streak-infected seedlings. Preference to feed on healthy seedlings will encourage spread of MSV disease. The four vectors differed significantly in five out of eight stylet penetration behaviours studied. Cicadulina mbila, an efficient vector, spent significantly more time than others in non-probing activities, least time feeding from phloem and overall probing. This behaviour will enhance its spread of MSV disease. Time spent on feeding in mesophyll and penetrating phloem (X-wave) was also significantly different among the four vectors. The efficiencies of C. mbila and C. storeyi in transmitting MSV, as compared to the other two species, may also be linked to longer pathway activities and shorter probe mean although the effects were not statistically significant. Time spent on pathway activities followed expected ranking of the vectors’ transmission efficiencies. Longer time for active feeding, searching for phloem cells and salivation would encourage efficient acquisition and inoculation of the virus.
Key Words: Cicadulina spp., electrical penetration graph, MSV, Zea mays