THE BIOLOGICAL CONTROL OF THE WATTLE BAGWORM, KOTOCHALIA JUNODI (HEYL.), BY A VIRUS DISEASE

To obtain further information about the effect of virus on wattle bagworm and on the course of an infestation cycle, suspensions of various concentrations and different origins were tested in 1957 against both young and old larvae. Virus of suspected low virulence and suspensions with and without adjuvants were also compared. With infestations in the prodromal stage and the larvae in their first instar at the time of treatment, mortality was similar with suspensions containing 1000 or 500 polyhedra/mm. 3 . Mortality was less with 250 polyhedra/mm. 3 , but still high enough to keep the crowns of the infested trees green. With the higher concentrations, the course of the cycle was greatly accelerated and the eruptive stage and the crisis occurred later in the same season, whereas, with the lowest concentration, the infestation decreased gradually after spraying. Against older larvae, the initial mortality was too low to prevent defoliation, but 9 months after spraying the mortality had increased sufficiently to reduce the infestation to its latent stage. Where virus was applied during the eruptive stage, there was a very high initial mortality, and defoliation of trees was light, whereas untreated trees were completely defoliated. Nine months after spraying, however, mortality was equally high in treated and untreated plantations. Viruses from different sources differed considerably in the mortality they caused. Virus introduced from a distant source was more effective than local strains, and at the prodromal stage was more successful in preventing defoliation and loss of yield. Methyl cellulose, used as a sticker, did not affect mortality, but skim‐milk powder decreased it. Artificially disseminated virus can not only cause epizootics in the treated plantations, but can also spread to neighbouring blocks in the years following treatment.