Marigold Blister Beetle

📖 Description

Mylabris pustulata, the Marigold Blister Beetle, is a large, conspicuous meloid beetle whose adults are sporadic but locally serious pests of marigold and other ornamental crops in India. The species belongs to the Meloidae, a family famous for its production of cantharidin — a powerful terpenoid blistering agent that protects the beetles from vertebrate predation. Cantharidin is sufficiently toxic that the beetles have no significant vertebrate predators; only certain specialist parasitoids and pathogens attack them. The lifecycle of blister beetles is among the most complex in the Coleoptera — it is called ‘hypermetamorphosis’ and involves several radically different larval forms. The first instar, called a ‘triungulin’, is highly active and long-legged; its sole purpose is to locate a grasshopper egg pod in the soil. Once the triungulin finds a pod, it moults into a grub-like form that feeds on the grasshopper eggs — making the larval stage a beneficial natural enemy of grasshoppers, which are themselves serious agricultural pests. The adult stage, by contrast, is a flower-feeding pest. This duality — beneficial larvae and pest adults — makes blister beetle management uniquely challenging: broad-spectrum soil-applied insecticides would suppress the larvae but harm the natural-enemy function they provide. The species is therefore best managed by hand-picking adults from flowers, which is labour-intensive but effective in small-to-medium marigold plantings. In India, the pest is most active during the post-monsoon period (July–October) when marigold is in peak bloom for the Dusshera and Diwali festival season — the timing makes the pest particularly economically damaging because festival-season flowers command premium prices.