Old European Silkworm Breeds Reared in Early-20th-Century Bulgaria and Their Potential Use in Modern Sericulture

Since local egg production using Pasteur's method began in 1895, two local silkworm breeds have mostly been reared in Bulgaria, namely, Yellow local and White Baghdad. The Yellow local breed is said to have originated and been reared from local breeds spread in northern and southwestern Bulgaria in the 16th-19th centuries, while White Baghdad originated from Asia Minor and was reared in southeastern Bulgaria. The Yellow local breed is characterized by yellow cocoons with an elongated shape with slight constriction. The white Baghdad breed consists of three types, namely the Edirne, Improved Bulgarian, and Bulgarian types. The cocoon color varies from snow white to light green, but the prevailing color is white. The cocoon shape is elongated, with constriction. The old silkworm breeds reared in 1920s-1930s Bulgaria were generally characterized by a non-uniformity of larval color and markings, as well as of cocoon color and shape, with comparatively high cocoon weights but lower silk shell percentages and filament lengths; they were also comparatively tolerant to NPV disease. Due to the long maintenance of these breeds in Bulgaria, they have become well adapted to the local food and climatic conditions. Presently, the Yellow local strain displays high hatchability and survivability, shorter fifth-instar duration, and a comparatively good reproduction capacity. On the other hand, it manifests lower values of main productive characteristics, such as cocoon weight, silk shell weight and percentage, silk filament length and weight, reelability, and raw silk percentage as compared with commercial Bulgarian white-cocoon breeds. Therefore, in order for this breed to be commercialized today, it needs to be improved by way of genetics and breeding. This paper includes a review of the literature on the inheritance of main qualitative characteristics in silkworms, as well as recommendations for future studies on improving old silkworm breeds.