Abstract

Honey bees are affected by various diseases caused by viruses, bacteria, fungi and mites. Of these, the Thai Sac Brood virus (TSBV) disease attacking Indian honey bee has been posing threat to hives of Apis cerana indica F. in different parts of Southern India. The virus is caused by picorna-like virus characterized under Iflaviridae family. The symptoms of TSBV are perforated brood scattered among capped brood, the presence of prepupae with typical raised and pointed heads in the comb cells, the dead larvae turn into sac-like structure filled with milky white fluid which when lifted up ruptured easily. Infective broods are odourless and show no ropiness. These symptoms were clearly visible in the present study. Studies conducted on the seasonal incidence of the disease revealed the prevalence of the disease during winter (October to January) season which prolonged to spring (Late January to March) season and was influenced by brood rearing. The TSBV disease incidence decreased in the month of April (2 / 30 colonies infected, 80 cells infected / colony) when the mean maximum temperature (34.3oC) was high while the relative humidity (RH 65%) and rainfall (62.7 mm) were low. In the succeeding four months namely May, June, July and August, the disease incidence was nil. The disease incidence started again in the month of September and reached a peak in the month of November (9 / 30 colonies were infected, 342 cells infected / colony) at which time the mean maximum temperature was low (28.6oC) while the RH (82%) and rainfall (191.3mm) were high. Thus the high disease incidence was found to be significantly correlated with low temperature and non significantly correlated with high RH and rainfall. The disease incidence also coincided with the active brood rearing period (November to March). Electron microscopic study of purified virus particles revealed that the virus is 32.3 ± 0.7 nm in diameter and icosahedral in shape. The morphology was found to be similar to that of sacbrood virus attacking Italian honey bee, Apis mellifera.

Keywords: Thai sacbrood virus (TSBV), Epidemiology, Honey bee, TEM, Picorna virus.