Comparison of tolerance to sunlight between spatially distant and genetically different strains of <i>Lymantria dispar</i> nucleopolyhedrovirus

<div><p>Baculoviruses are a family of insect-specific pathogenic viruses can persist outside for long periods through the formation of occlusion bodies. In spite of this ability, the UV of sunlight is an essential factor that limits the survival of baculoviruses outside the host. In the current study, we compared the UV tolerance of two strains of <i>Lymantria dispar multiple nucleopolyhedrovirus</i> (<i>LdMNPV</i>), which were isolated in spatially different regions (<i>LdMNPV</i>-27/0 in Western Siberia (Russia) and <i>LdMNPV</i>-45/0 in North America (USA)) and dramatically differ in their potency. We exposed the studied strains to sunlight in an open area for 0.25, 0.5, 1, and 2 hours and later perorally inoculated host larvae with the same doses of virus (5x10⁵) and with doses leading to same effect (LD₉₀). We observed that strain <i>LdMNPV</i>-45/0, which previously showed high virulence against <i>L</i>. <i>dispar</i> larvae, was more sensitive to UV irradiation (estimated as the relative rate of inactivation (<i>r</i>, h ^-1) and as the half-life of the virus (τ_1/2, h)) compared to <i>LdMNPV</i>-27/0. Exposure to sunlight induced a significant delay of <i>LdMNPV</i>-45/0-induced pathogenesis already after 0.25 h of sunlight exposure, while for <i>LdMNPV</i>-27/0 this delay was occurred only after 2 h exposure in spite of used concentrations. We also compared the sequences of the main structural proteins of the studied strains as UV light contributes not only to genome damage in viruses but also to structural protein damage. The most prominent genetic difference between the structural proteins of the strains was related to the loss of the virus enhancin factor-1 (<i>vef-1</i>) gene in the <i>LdMNPV</i>-27/0 strain. Thus initially highly potent viral strain (such as <i>LdMNPV</i>-45/0) is not recommend to use in the regions (or forest stand density) with high UV load. The role of virus enhancin factor-1 in baculovirus tolerance to UV needs for following studies.</p>