Prevalence of latent virus in Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) and its activation by a heterologous virus

Abstract

Nested PCR amplification of a Spodoptera litura nucleopolyhedrovirus (SpltNPV) lef-8 gene fragment was performed on egg masses and larvae of S. litura, and resulted in detection of a latent SpltNPV in 20.0% of "healthy" laboratory stock samples, and in 22.6% of samples collected at different periods and in remote places in Kagoshima Prefecture. The PCR product sequences showed 99% similarity to the published lef-8 sequence of SpltNPV, confirming that the amplification products were derived from SpltNPV. Further, cross-inoculation of laboratory stock S. litura larvae with Mythimna separata NPV (MyseNPV) activated the latent virus, which provoked a change in the virulence of MyseNPV samples collected from cadavers of S. litura. Our data suggest that caution should be taken when using S. litura as a host to produce heterologous NPVs.

Pathogen Persistence in the Environment and Insect-Baculovirus Interactions: Disease-Density Thresholds, Epidemic Burnout, and Insect Outbreaks

“…As we have described, however, evidence for covert infections in the lab is stronger for at least a few other insects (Burden et al 2003, 2006; Kouassi et al 2009; Vilaplana et al 2010) than it is for the gypsy moth (Myers et al 2000; Ilyinykh et al 2004), and so this conclusion may not be general. An additional caveat is that our models assume that spatial structure plays little role.…”

“…If such latent virus is activated, the host may die of the infection, leading to horizontal transmission that may spark an epidemic. Existing data consist of observations of virus outbreaks in laboratory populations held under sterile conditions (Burden et al 2006), and detection, using PCR, of viral DNA in individuals in the field (Burden et al 2003; Kouassi et al 2009; Vilaplana et al 2010). The latter data often reveal high latent infection rates, and so covert infections would seem to have the potential to play an important role in baculovirus dynamics.…”

Intra- and Intergenerational Persistence of an Insect Nucleopolyhedrovirus: Adverse Effects of Sublethal Disease on Host Development, Reproduction, and Susceptibility to Superinfection

“…The genetic factors associated with latent or sublethal infection are poorly understood in baculoviruses, although a number of examples in the published literature have provided evidence that infection with a heterologous NPV can trigger a sublethal infection into a lethal state of disease (5,12,13,19). Further experiments are required to elucidate the conditions under which sublethal infections can be activated to kill the host, but this strategy may be clearly advantageous to the resident virus when it detects the presence of a competing pathogen.…”

Chemical and biological stress factors on the activation of nucleopolyhedrovirus infections in covertly infected Spodoptera exigua

“…; Kouassi et al. ). For example, wild‐type SeMNPV and MbMNPV‐like genomes were detected in the OBs collected from virus‐killed S. exigua larvae that had previously been injected with SeMNPV recombinant DNA, suggesting the presence of covert infections by both the heterologous virus and the homologous wild‐type virus in the insect population (Murillo et al.…”

“…Such infections have been termed sublethal or covert and are likely widespread in lepidopteran populations (Kouassi et al. ; Burand et al. ; Cabodevilla et al.…”