Pathogenicity and Conurol of Bacillus larvae in Honey Bees

• Main Authors: Chen, Yue-Wen, 陳裕文
• Other Authors: Ho Kai-Kuang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/90309558660356604994

博士 === 國立臺灣大學 === 植物病蟲害學系研究所 === 85 === Pathogenicity of Bacillus larvae spores to 1-day-old larvae, Apis mellifer a, was determined by experimental infection in Taiwan. The results showed no s easonal difference in mortality of larvae. Infected individuals showed AFB sig ns in the capping stage, while 32.2% - 46.3% died in the larval stage resulted from heavy infections. The 1-day-old larvae are highly susceptible toB. larva e, LD50 and LD95 are 21 spores and 442 spores, respectively. In contrast, the mortality of 2-day-old larvae to B. larvae was much lower than that of 1-day-o ld larvae. The mortality of 2-day-old larvae was 37.2% ±3.4% after 4.5×10^4 spores/larva inoculation, while 3-day-old larvae were not susceptible to this pathogen even at the same dose. By experimental infection with B. larvae s pores to native Asian honeybee (A. cerana), 1-day-old and 2-day-old larvae wer e susceptible to this pathogen, and showed the AFB symptom like the infected E uropean honeybee individuals. However, high tolerance of A. cerana compared wi th that of A. mellifera was found. Results showed that mortality of 1-day-old larvae of A. cerana was 47.1%±10.2% after 442 spores/larva (LD95 of A. mellif era) inoculation, and mortalityof 2-day-old larvae was 23.3% ±5.0% after 4.5 ×10^4 spores/larva inoculation. Natural outbreak of AFB occurred rarely in As ian honeybee colonies, the considerable factors may consist of : (1) less susc eptibility in A. cerana larvae, and their resistant mechanism may be relation to midgut systems, not toimmune systems of pupal haemocoel. (2) most of infect ed larvae (61.1% -82.2%) were ejected in the larval stage by the hygienic beha vior of A. cerana, and thatof decreased spore contamination in their hive. In vitro tests, oxytetracycline (OTC) showed the highly inhibitory effect onv egetative cells of B. larvae (MIC = 0.016 μg/ml), but no sporicide effect. In field tests, honeybee colonies were medicated with OTC syrup to determine thei reffectiveness on young larvae prevention of AFB. Results showed 2 doses of OT C syrup, 125 mg/colony and 50 mg/colony, prevent AFB signs for a period of, at least, 9 days and 3 days, respectively. The ethanol extracts of Taiwanese pro polis also showed a good inhibitory effect on vegetative cells of B. larvae (M IC = 3.125μg/ml) in vitro, while colonies medicated twice with 400 mg/colony treatments only had a limited effect in field tests. Colonies with a light AFB infection treated with hive replacement recovered from the disease and no AFB recurrence in a investigated period of 15 weeks. Beside the hive replacement, colonies with a heavy infection should be medicated additionally with 125 mg of OTC on the 5th day post-replacement. OTC medication colonies should be stop ped harvesting for a month. Honey stored during medication periods in combs sh ould be removed before another harvests. An artificial method was developed for rearing worker honeybee (A. mellifera) larvae to the adult stage in the l aboratory . This method subsequently was used in studying the effects of OTC a nd propolis extracts on larval growth and development. A general dose response was observed in mortalities of larvae fed diets supplemented with 60 ppm to 1 50 ppm OTC or 500 ppm propolis extracts. At 25 ppm OTC or 100 ppm propolis ext racts in diets, larval and postdefecation mortalities, and larval growth rates were similar to the controls, while higher than these doses retarded larval g rowth and caused higher mortality. When fed with 0.2 ppm, OTC effectively redu ced larval and postdefecation mortalities of larvae inoculated with 4.5×10^5 spores/ml. However, fed even up to 100 ppm , propolis extracts could not preve nted the AFBinfection. It revealed that OTC effectively protected young larvae from B. larvae infection, while propolis extracts did not.