Bioassaying an insect virus on leaves. II. The influence of certain factors associated with the larvae and the leaves

The importance of certain factors which act through the larvae or through the leaves when a virus suspension is bioassayed by applying a known volume in droplets to a leaf of standard size has been investigated. The most critical was the age of the second-instar larvae. In 24 hr their resistance to infection increased significantly. On the other hand, starving the test larvae for 6 hr to assist randomization of factors that influenced the area of treated leaf consumed did not produce a measurable effect on mortality. A 2°C increase in the temperature reduced the incubation period of the disease but produced no effect on the final kill due to the virus. The practical implications of these results are discussed in relation to the bioassay procedure.