Ecological bottlenecks and future pathways for Zygogramma bicolorata as a biocontrol agent of Parthenium hysterophorus in North India

The aggressive invasion of Parthenium hysterophorus across India has driven the deployment of the host-specific beetle Zygogramma bicolorata as a classical biocontrol agent, achieving episodic but geographically inconsistent suppression. The core limitation is a phenological mismatch, where the beetle’s obligate diapause creates a temporal refuge for early-season weed growth, allowing these cohorts to contribute significantly to the persistent soil seed bank. This review synthesizes evidence to propose a revitalized, precision-management framework. Central to this strategy are augmentative releases to correct seasonal asynchrony, selective breeding of low-diapause beetle strains, and the deliberate integration of Z. bicolorata with the guild of resident native herbivores. Expected outcomes include a 40–60% reduction in early-season weed biomass, a 50–70% decline in soil seed bank replenishment within 3–5 years, and restoration of native plant diversity to near pre-invasion levels. Practically, this framework enables managers to transition from episodic suppression to predictable, landscape-level control, reducing herbicide dependency by an estimated 30–50% and lowering annual weed management costs. This integrated, data-driven approach aims to transform a partially successful program into a reliable and sustainable cornerstone for landscape-level control of P. hysterophorus in India.