In its long-awaited report expected for late 2015, the US Environmental Protection Agency has concluded that neonicotinoids (neonics) pose a “significant risk” to honeybees when used on cotton and citrus but not when used on other big crops like corn, berries and tobacco.

Results of tests on other crops, including legumes, melons, tree nuts and herbs, were inconclusive and needed more testing, the agency said. But it noted that the practice of treating seeds with the chemical “seemed not to harm bees.”

EPA said it focused only on honeybees as these are “a good surrogate” for all pollinators.

The agency said its analysis of detailed tests performed by major producer Bayer CropScience on its behalf found a clear level of concentration of the most common neonicotinoid, imidacloprid. Here it determined 25 ppb to be the highest tolerable level.

Some environmental advocacy groups have laid the blame for the widespread decline of honeybee populations largely on neonicotinoids, which led the EU in 2013 to implement a two-year moratorium on its use. Scientific studies in some cases have backed up suggestions that confirm the negative potential, but the agrochemical industry disputes these.

One study published last year suggested that neonics in general may harm bumblebees, but not honeybees, whereby a University of Illinois entymologist called this and another study published in 2015 “more nails in the systemic neonicotinoid coffin.”

The first scientific long-term US risk assessment of the controversial class of pesticides did not present a clear answer that would provide justification for an outright ban; nor did it offer a blanket go-ahead for continued use, observers said. EPA plans to proceed with four other tests – initial reports pointed to six – and seek public comment before acting to restrict any products.