Comparison of the Activity Enhancement of a Baculovirus by Optical Brighteners Against Laboratory and Field Strains of Choristoneura occidentalis (Lepidoptera: Tortricidae)

Abstract

The enhancement of Choristoneura fumiferana(Clemens) multicapsid nuclear polyhedrosis virus (CfMNPV) activity by 4 optical brighteners was compared in the laboratory between nondiapausing laboratory and diapausing field strains of the western spruce budworm, C. occidentalis.The laboratory strain was 2.7 times as susceptible to the virus as the field population in terms of LD50 (dose at which 50% of the tested larvae died). When a 1% concentration of optical brightener was added to the virus, lethal doses for both strains were significantly reduced, indicating that all 4 brighteners acted as activity enhancers for CfMNPV. In terms of LD50, brighteners enhanced viral activity against the field strain more (7.6–11.0 times) than the laboratory strain (2.5–3.5 times). Although there were differences in larval susceptibility to CfMNPV between the 2 strains, LD50 values for both strains were reduced to the same levels when 1% brightener was added to the virus. Furthermore, the larvae died more quickly with the addition of brighteners. The time required to kill 50% of the larvae was reduced by 39–60% for the field strain, and by 43–57% for the laboratory strain by the addition of 1% brightener.