May 2000. In the last few years, Bunchy top virus of banana has been found in New Caledonia and eradication has been attempted. A question was asked about the effectiveness of parasitoids of the vector of BBTV, the banana aphid, Pentalonia nigronervosa.

The parasitoid, Aphidulus colemani, was introduced into Tonga for the control of P. nigronervosa, but with little success. Although 30,000 A colemani mummies were released, only one was found in the following 4 weeks. The strategy was to focus on taro, often infested with Aphis gossypii, to create a reservoir of the parasitoid which would later attack P. nigronervosa. It did establish on A gossypii, but there was no evidence, even after 2 years, that it had established on P. nigronervosa. Trials showed that ants prevented predators (lacewing larvae and syrphid flies) populations from building up on banana, and it is likely that ants also interfered with the establishment of the parasitoid.

It would seem that eradication is the best method of control:

• spray the banana with insecticide or kerosene to kill the vectors as soon as symptoms are see
• dig out the whole stool, cut it into pieces, dry and burn or bury it
• did out any regrowth and destroyed in the same way
• K-PINS treated with picloram can be used, but with caution. They leave a residue in the soil and in Samoa replants would not grow if planted in the same hole as the treated plant. If planted to the side they grew normally
• direct injection of gyphosate into stems and suckers (with an injector gun) is an effective method to destroy the plants. But there is still need to destroy the aphids before they have the chance to migrate.

Host range of BBTV was also questioned, and QUT, Australia, provided the following information.

Host range studies have shown that BBTV can be transmitted to four species of the Musaceae, namely Musa acuminata, M. balbisiana, M. acuminata x balbisiana, and M. textalis, as well as Ensete ventricosum (Welw.) E.E. Cheesm. Attempts to transmit the virus to the closely related genera of Strelitzia sp. (Musaceae), Ravenala sp. (Musaceae), Canna sp. (Cannaceae), and the unrelated Solanum tuberosum (Solanaceae), or Zea mays (Gramineae), were apparently unsuccessful.Several studies have been done to determine whether natural reservoirs of the virus exist. It has been reported that Colocasia esculenta (L.) Schott. could be symptomlessly infected with BBTV. This has important epidemiological significance because this species is widespread in many areas where the virus occurs and serves as a host for the aphid vector of BBTV, Pentalonia nigronervosa. However, further confirmation of this is required.

Several other non-Musa species, including Canna sp. and Heliconia sp. have also been implicated as reservoirs of BBTV based on the presence of BBtd-like symptoms in the field. These findings, again, need to be confirmed by transmission experiments or other more specific diagnostic tests. All species, cultivars, or types in the genus Musa that have been tested have been shown to be susceptible to BBTV. However, some variations have been reported between cultivars regarding the efficiency of infection.

In studies reported by DPI Brisbane to infect H psittacorum cv. Red Parakeet with an Australian BBTV isolate, 0/10 plants became infected (Geering, ADW and Thomas J (1997). Australasian Plant Pathology 26(4): 250-254.

Photos of bunchy top virus disease can be seen at: http://www.ctahr.hawaii.edu/banana