The Helicoverpa armigera Nucleopolyhedrovirus (HaNPV) operates through a sophisticated biological process that transforms a single infection into a field-wide plague.
- Mode of Action: A Precise Stomach Poison
HaNPV acts as a stomach poison. When a bollworm larva consumes leaves treated with the virus, the viral polyhedra dissolve in the highly alkaline environment of the insect’s midgut. This process releases active virus particles that invade the midgut epithelial cells and subsequently spread to the entire body. - Lethal Progression: 3 to 7 Days to Impact
Once infected, the larvae typically perish within 3 to 7 days. A signature trait of this infection is that dead larvae are often found hanging upside down from the top of the plant—a behavior driven by the virus to maximize its spread. - The “Liquefaction” Effect & Secondary Infection
Upon death, the insect’s outer skin ruptures, releasing a liquid filled with billions of new virus particles (often referred to as the “liquefaction” or “melting” phenomenon). This virus-rich fluid is then dispersed by wind and rain, contaminating nearby foliage and triggering a secondary infection cycle. This creates a natural “epidemic” effect that continues to control the pest population long after the initial
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