Lethality of injected peach Western X-disease virus to its leafhopper vector

Insect injection and artificial feeding bioassays to test the vector specificity of flavescence dorée phytoplasma

ABSTRACT The specificity of vector transmission of Flavescence dorée phytoplasma (FDP) was tested by injecting FDP, extracted from laboratory-reared infective Euscelidius variegatus, into specimens of 15 other hemipteran insect species collected in European vineyards. Concentrations of viable phytoplasma extracts and latency in vectors were monitored by injection of healthy-reared E. variegatus leafhoppers. Based on these preliminary results, insects were injected by using phytoplasma extracts that ensured the highest rate of FDP acquisition and transmission by E. variegatus. Transmission into an artificial diet through a Parafilm membrane about 3 weeks after insect injection was attempted. FDP-injected insects that belonged to 15 hemipteran species were confined in cages and fed through the membrane for a 4- to 5-day inoculation access period. FDP DNA was detected by polymerase chain reaction (PCR) in the feeding buffer fed upon by Anoplotettix fuscovenosus, Aphrodes makarovi,E. variegatus, and Euscelis incisus. PCR amplification with specific primers detected FDP DNA in injected insects of all test insect species. Band intensity was positively correlated with the transmissibility of FDP. Transmission of FDP to plants by feeding was confirmed for Anoplotettix fuscovenosus, E. variegatus, and Euscelis incisus, but not for Aphrodes makarovi. Our results suggest that vector competency of FDP is restricted to specimens belonging to the family Cicadellidae, subfamily Deltocephalinae.

Evidence on Possible Mycoplasma Etiology of Aster Yellows Disease II. Suppression of Aster Yellows in Insect Vectors

Chlortetracycline or chloramphenicol (but not kanamycin, penicillin, or erythromycin), when administered in hydroponic solution to diseased aster, reduced the availability of the aster yellows (AY) agent to nymphs of Macrosteles fascifrons (Stål). Insects exposed to healthy plants whose roots were immersed in chlortetracycline were able to acquire AY agent from diseased plants the day after removal from the antibiotic-treated plants, but the latent period of the ensuing disease in the insects was prolonged. Chlortetracycline or tylosin tartrate blocked AY infection in nymphs injected with a mixture of antibiotic and the AY agent, but polymyxin, neomycin, vancomycin, penicillin, carbomycin, or chloramphenicol did not. All tetracyclines tested, methacycline, oxytetracycline, and chlortetracycline, produced a dramatic reduction in the ability of infected vectors to transmit AY agent. Tylosin tartrate also reduced transmission when injected into AY-transmitting vectors, but carbomycin, spectinomycin, cycloserine, penicillin, erythromycin, or kanamycin had no such effect. During the first 10 days after injection of tylosin tartrate or oxytetracycline into transmitting vectors, ability of the insects to transmit AY decayed rapidly. Transmission by insects injected with buffer alone, after decreasing the first day after injection, gradually returned to its normal level in less than 1 week. By 2 to 3 weeks after injection with tylosin or oxytetracycline, ability to transmit AY was regained by vectors. The results suggest that tetracycline antibiotics and tylosin tartrate inhibit multiplication of AY agent in the insect. The spectrum of antibiotic activity in the insect is consistent with the hypothesis that AY and other plant yellows diseases are caused by mycoplasma-like organisms.