Larvae also lose their plump appearance and look undernourished. In such cases, larval remains appear twisted or melted to the bottom of the cell. They form a thin brown or blacklsh-brown scale and show distinct lines where their breathing tubes are located. Recently dead larvae are rarely ropy. Scales can be removed easily from the cells because they are rubbery rather than brittle as in American foul-brood.
Bees remove the scales under the stimulus of a nectar flow or feeding.
Streptococcus pluton does not form spores, but the organism often overwinters on combs. It gains entry into the larva in contaminated brood food and multiplies rapidly within the gut of the larva. Not all infected larvae die from the disease. Some develop normally and void the germ or regurgitate the bacteria onto the underside of the cappings, which then become sources of the disease. Since the honey of infected colonies is contaminated, EFB can be spread by robber bees or by the interchange of contaminated equipment among colonies and drifting bees.