NEW DELHI — Over the centuries, the Taj Mahal has endured its share of attacks — plundered by the Jats of northern India and looted by British soldiers, among other indignities. In recent years, officials have worried that growing air pollution could permanently darken the tomb’s brilliant white exterior. But few people anticipated the latest affront — millions of mosquito-like insects, their numbers supercharged by nutritious algae blooming profusely along the banks of the polluted Yamuna River nearby. Like generations of romance-driven human couples before them, the bugs have swarmed the Taj Mahal on a mating flight, excreting a green substance on parts of its marble walls. The Yamuna has suffered mightily in recent years from the dumping of solid waste in its waters, says an environmental activist in Agra, India, the site of the Taj Mahal. “I have been constantly watching how the river pollution has gone from bad to worse,” said D.K. Joshi, who filed a petition over the insects in the National Green Tribunal, an environmental court last week. “The encroachments on and around the riverbed, the sewage going directly into the river” are choking it, he said. With India’s cities ranking among the most polluted in the world by the World Health Organization, public concern over toxic air and water is mounting. The central government has pledged billions of rupees to cleaning the Ganges River. But the effect of pollution on India’s cultural heritage, though less obvious than its health effects, is also worthy of attention, experts say.