Male-killing virus in a noctuid moth Spodoptera litura

Area of Science:

• Virology
• Arthropod biology
• Genetics

Background:

• Cytoplasmic elements often benefit from female-biased sex ratios in hosts.
• Bacterial symbionts and some viruses (Partitiviridae) are known to cause male killing in arthropods, skewing sex ratios.

Purpose of the Study:

• To investigate if male-killing viruses are limited to the Partitiviridae family or exist in other viral taxa.
• To identify and characterize a novel male-killing virus in the tobacco caterpillar, Spodoptera litura.

Main Methods:

• Isolation and injection of Spodoptera litura male-killing virus (SlMKV) into uninfected S. litura.
• Maternal inheritance studies of SlMKV.
• Genomic analysis of SlMKV.
• Transinfection experiments into S. litura larvae.
• Analysis of viral RNA levels during embryonic and pupal stages.

Main Results:

• SlMKV, a maternally inherited RNA virus, was identified as causing male killing in Spodoptera litura, resulting in all-female broods.
• SlMKV can be transmitted maternally and experimentally induced via injection.
• The virus has a unique genome, lacks known male-killing genes, and belongs to an unclassified viral group.
• Male hosts die at the pupal stage, with viral RNA levels suggesting constitutive expression of lethal products.

Conclusions:

• Diverse RNA viruses in arthropods can independently evolve male-killing capabilities.
• SlMKV represents a novel example of a male-killing virus outside the Partitiviridae family.
• These viruses may play a significant role in intragenomic conflicts within arthropod populations.