The Optimal Timing for Applying Juvenile Hormone Analogue Pyriproxyfen to Hybrid Silkworm, Bombyx mori L., Leung Saraburi Strain (J108 x Nanglai Saraburi)

Abstract

This research aimed to determine the optimal timing for applying Juvenile Hormone Analogue, Pyriproxyfen to increase silk yields in the hybrid silkworm, Bombyx mori L. Leung Saraburi Strain (J108 x Nanglai Saraburi). At a concentration level of 0.05 ppm, 50 µl, the pyriproxyfen solution was applied by utilizing a topical method on fifth instar silkworms in six different experimental groups divided into days: day 1, day 2, day 3, day 4, day 5 and day 6 of fifth instar larvae. The control group was topically applied with distilled water. Once spinning was complete, growth characteristics and silk yields data were collected from all groups and statistically analyzed. The results revealed that the percentage of normal cocoon and normal pupae in the day 5 and day 6 groups was significantly lower (P<0.05) than in the control and other experimental groups. On the other hand, in the day 1, 2, 3, and 4 groups, percentage of normal cocoons and normal pupae were high but were not statistically different (P>0.05) compared to the control group. In comparison, the silk yields characteristics, the cocoon weight, cocoon shell weight, silk filament weight and length of silk filament, in the day 3 and day 4 groups statistically significantly increased (P<0.05) compared to the same characters of the day 1 and day 2 groups. The length of silk filament of the female cocoon on the day 3 and day 4 groups was 1099.65 and 1169.15 metres which were longer than in the day 1 and day 2 groups, 997.07 and 980.01 metres, respectively. In conclusion, the results indicated that the silk yield was most significant in the day 3 and day 4 groups. Therefore, the third and the fourth day of the fifth instar are the optimal times for pyriproxyfen administration in the Bombyx mori L. Leung Saraburi Strain.