Study on silkworm bed cleaning frequency during larval growth period

Abstract

Bed cleaning is an important silkworm rearing process to ensure the hygiene in the immediate vicinity of silkworms in order to protect  from disease infection and to ensure them good feeding appetite. Hence, timely bed cleaning is essential to keep the worms healthy and  productive. The treatments used for this study were one time bed cleaning frequency per instar, two times bed cleaning frequency per  instar, three times bed cleaning frequency per instar, once bed cleaning frequency per day, twice bed cleaning frequency per day and no  bed cleaning (control) to evaluate the effects of silkworm bed cleaning frequencies on silkworm races. Observations on larval mortality,  larval period, single cocoon weight, shell weight, length of silk thread and silk ratio were carefully noted for each treatment and  replications. Three replications were used for each treatment. Once bed cleaning frequency per day, twice bed cleaning frequency per  day and three times bed cleaning frequency per instar significantly (P < 0.05) shortened the larval period of Vietnamese eri-silkworm  races (23.7, 25 and 24.3 days), Indian eri silkworm races (29.8, 28.6 and 29.6 days), Kenyan bivoltine silkworm races (27.5, 30.6 and 31.5  days), Korean bivoltine silkworm races (24.7, 25.3, and 25.8 days) and Vietnamese multivoltine silkworm races (25.7, 25.8, and 25.8 days)  respectively as compared to the untreated check which was 36.3 in Vietnamese eri, 55.4 days in Indian eri, 33.1 days in Kenyan bivoltine,  30.2 in Korean bivoltine and 30.3 in Vietnamese multivoltine silkworm races. Larval mortality was significantly higher for Vietnamese eri- silkworm races (8.25 & 15.58%), for Indian eri-silkworm races (5.01 & 11.66%), for Kenyan bivoltine silkworm races (12.2 & 30.06%), for  Korean silkworm races (13.83 & 32.83%), for Vietnamese multivoltine silkworm races (0.33 & 45.5%) for the mature larval stages of 4 th  and 5 th larval instars respectively in the untreated silkworm rearing beds. Among the tested treatments, three times bed cleaning  frequency per instar, one time bed cleaning frequency per day and two times bed cleaning frequency per day significantly reduced larval  mortality rate during the 4 th and 5 th larval instars of all silkworm races which was ranged between 0 to 0.33% for Vietnamese eri- silkworm races, 0.58 to 7.15% for Indian eri-silkworm races, 0.9 to 14.13% for Kenyan bivoltine silkworm races, 1 to 5.16 % for Korean  silkworm races and 0.33 to 0.83% for Vietnamese multivoltine silkworm races. The young larval stages/instars (1st to 3rd instars) showed low larval mortality rate than mature larval stages (4th and 5 th instars) in all silkworm races. Bed cleaning frequencies had no significant  effect for 1 st instar for all silkworm races. All bed cleaning  frequencies had no significant effect for Korean silkworm races and  Vietnamese multivoltine silkworm races until the 3rd instars. Hence, bed cleaning is not necessary during these stages in silk worm  rearing practices for such races. Bed cleaning has showed a positive effect to reduce larval mortality rate for Vietnamese eri-silkworm  races, Indian eri-silkworm races and Kenyan bivoltine silkworm races during 2nd and 3rd larval growth. Long spinning silk thread, robust silk cocoon and shell weight and higher percentage of silk ratio of silkworm races were registered from one time bed cleaning  frequency per day and two times bed cleaning frequency per day.