Comparison of tolerance to sunlight between spatially distant and genetically different strains of Lymantria dispar nucleopolyhedrovirus

Abstract

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 Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV), which were isolated in spatially different regions (LdMNPV-27/0 in Western Siberia (Russia) and LdMNPV-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 LdMNPV-45/0, which previously showed high virulence against L. dispar larvae, was more sensitive to UV irradiation (estimated as the relative rate of inactivation (r, h -1) and as the half-life of the virus (τ1/2, h)) compared to LdMNPV-27/0. Exposure to sunlight induced a significant delay of LdMNPV-45/0-induced pathogenesis already after 0.25 h of sunlight exposure, while for LdMNPV-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 (vef-1) gene in the LdMNPV-27/0 strain. Thus initially highly potent viral strain (such as LdMNPV-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.

Influence of delayed density and ultraviolet radiation on caterpillar baculovirus infection and mortality

“…A study of baculovirus transmission in forest tent caterpillars ( Malacosoma disstria ) found depressed transmission rates on forest edges as opposed to the forest interior, which was attributed to sunlight inactivating virus on leaves at forest edges (Roland & Kaupp, 1995). A field study of two strains of gypsy moth NPV showed variable resistance of virus to ultraviolet, in which inactivation rate from ambient ultraviolet was greater in a more potent strain than a less potent one (Akhanaev et al, 2017). In another study of forest tent caterpillars using tree ring analyses, it was suggested periods of weaker ultraviolet radiation increased the effect of forest tent caterpillar outbreaks on tree growth (Haynes, Tardif, & Parry, 2018).…”

Effect of Ultraviolet radiation on Original Activity Remaining of Spodoptera littoralis NPV against S. littoralis Boisd (Lepidoptera: Noctuidae)

“…Effect of exposure periods to UV on virus was studied previously. Akhanaev et al, [25] studied the open area sunlight exposed virus strains for 0.25, 0.5, 1, and 2 hours and later per orally inoculated host larvae with the same doses of virus (5x10 5 ) and with doses leading to same effect ((Lethal Dose killing 90% of the insect pest (LD90)). Also, they observed that strain LdM NPV-45/ O, which previously gave high virulence against L. dispar larvae, was more sensitive to UV irradiation.…”

A Comparison of the Vertical Transmission of High- and Low-Virulence Nucleopolyhedrovirus Strains in Lymantria Dispar L.

“…To initiate infection, groups of 250 fourth instar larvae were allowed to eat leaf discs (dia = 8 mm) containing a dried drop of suspension of 4 × 10 4 OBs/disc for LdMNPV-45/0 and 2 × 10 5 OBs/disc for LdMNPV-27/0 as described in detail by Akhanaev et al, 2017 [ 39 ]. The doses used significantly differed for the low- and high-virulence strains.…”