On Artificial Diet

Scientific Papers. Series D. Animal Science. Vol. LXIII, No. 2, 2020 ISSN 2285-5750; ISSN CD-ROM 2285-5769; ISSN Online 2393-2260; ISSN-L 2285-5750 STUDY OF THE TECHNOLOGICAL CHARACTERS OF SILKWORMS (Bombyx mori L.) ON ARTIFICIAL DIET Krasimira AVRAMOVA Agricultural University, 12 Mendeleev Blvd, Plovdiv, Bulgaria Corresponding author email: [email protected] Abstract The purpose of the research is to prolong the period of silkworm rearing during the summer and autumn season. The rearing was carried out in the months of July, August and September at the Experimental Station of Sericulture at the Agricultural University in Plovdiv, Bulgaria. Silkworms in the first, second and third instars were fed by applying artificial diet, and in the last two larval instars – on mulberry leaves from Morus alba L. The results obtained from the studied technological characters show that there is a decrease in the basic values of the cocoon weight and filament length. For other characters, the decrease is negligible. The main conclusion is that the rearing of silkworms during the summer months by using combination of feeding on artificial diet in the first three instars and on mulberry leaves in the fourth and fifth instars is successful and leads to the possibility for more employment of people and increasing of the income of the silkworm rearers. Key words: Artificial diet, Bombyx mori L., Morus alba L. INTRODUCTION originated decades ago out of a simple query “Why do silkworms feed only on mulberry The specificity of the climatic conditions in leaves?”. This question caused a number of Bulgaria allows the rearing of silkworms with studies on the composition of mulberry leaves mulberry leaves to be carried out during the half and in particular on the compounds which of the year – from the beginning of May to the attracts the silkworms. Globally, continuous middle of October (about five months). efforts are being made to improve the Accordingly, there is an existing scheme of performance of artificial diet through silkworm eggs production, in which spring and permutations and combinations. However, all late-spring rearing are carried out with eggs existing silkworm breeds and hybrids might not produced in the previous year, summer rearing – thrive on artificial diet on default; instead they with treated with hydrochloric acid eggs from should be made adapted to the diet through spring generation, and autumn rearing – with breeding process (Nair et al., 2013). hydrochloric acid-treated eggs laid by Each of the ingredients involved in the silkworms of spring or summer generation. preparation of artificial diet can have a positive At the same time, in subtropical countries, the or negative effect on the main characters. rearing begins as early as March, while in most According to some studies, ascorbic acid in food tropical countries, it occurs throughout the year. affects the yield of cocoon. Rearing of In the countries of the Southern Hemisphere, the silkworms in their first and last instars on seasons of silkworms rearing are reciprocal to ascorbic acid-free diet has been shown to have a those in Bulgaria. beneficial effect to cocoon production without In India and Thailand, some of the best coconut affecting the survival rate or delaying the larval crops are harvested during the so-called cycle (Cappellozza et al., 2005). “winter” season from December to February. In In Japan, where the sericulture industry is one of the last decade in countries such as Japan, Italy, the most developed in the world, in about 50% USA, Canada, UK and others, year-round of the silkworms farming an artificial diet is silkworms rearing with so-called “artificial used during the young instars (Shimbo et al., food” has been developed. 1994). Although the use of artificial diet is The idea of developing artificial diet as a costly, since 6% of the costs are for agar-agar replacement of the fresh mulberry leaves and mulberry leaves (Shimbo et al., 1994). 13 Some recipes have also been developed in order Bulgarian silkworm breeds and hybrids under to feed silkworms on artificial diet using optimal and adverse rearing conditions during different percentages of mulberry leaves (5%, the last two larval instars. 15%, 25%) and applying the diet at different It was estimated that there existed clearly larval stages (Sbrenna et al., 2000). expressed genetically determined differences According to (Cappellozza et al., 2011), between the breeds and hybrids for pupation rate hormone-based preparations can be added to the under adverse silkworm rearing conditions. artificial diet, such as Methoprene (Manta) However, no any correlation was detected having a stimulating effect on the silkworms, between the pupation rate under the optimal and with an increase in protein accumulation in the adverse rearing conditions in one the same body that can be used later for biomedical strain. purposes. Different diets could also have a negative effect on protein accumulation in the MATERIALS AND METHODS body, immune system, digestion, nutrient uptake, metabolism and silk synthesis (Zhou et The experiments were conducted during the al., 2008). period 2017-2018 at the Agricultural University Sukirno et al. (2005) evaluate artificial diets that of Plovdiv. The tasks of our research were to can be used to successfully culture the atlas silk feed the silkworms on artificial diet during the moth, Attacus atlas L. The results of their first, second and third instars, and the silkworms studies show that in some of the characters there in their fourth and fifth instars we fed on are no significant differences, while there are mulberry leaves. some in others. Based on the results that were Two uni-bivoltine 4 molting pure lines, created obtained, they recommend adding extra protein in Bulgaria in 2005, namely Svila 1 and Svila 2, to the artificial diet. were tested. According to Saviane et al. (2014), the From each strain, there were employed three availability of quality mulberry leaves in the replicates with 200 larvae each. Same strains but temperate climate zone is restricted to the reared on mulberry leaves only were used as spring-summer season, which is a limiting factor references to collate the main technological in the selection of silkworm strains. Therefore, characters that have been studied. they carry out coupled traditional rearing on The standard method for the summer season was mulberry leaves with rearing on an artificial diet, applied for carrying out the incubation of in order to obtain increased larval efficiency in silkworm eggs. The conditions for silkworm converting food and high silk production. rearing on artificial diet compared to those Some authors (Tzenov et al., 2000) studied the applied for rearing with mulberry leaves only pupation rate and fresh cocoon yield in different are shown in Table 1: Table 1. Environmental conditions for silkworms rearing on artificial diet and on mulberry leaves Relative humidity, Instar Temperature, °C % Larvae fed on fresh mulberry leaves I 26-27 85-90 II 26-27 85-90 III 25-26 80-85 IV 23-25 70-75 V 20-25 65-70 Cocooning 24-26 70-75 Larvae fed on artificial diet I 29–30 90 II 29–30 90 III 27–28 80 IV 26 70–75 V 24 70 Cocooning 25–27 55–60 14 It can be seen that the temperatures established For determining the fresh cocoon weight and for the rearing on artificial diet differs from shell weight, the following approaches were environmental conditions required for rearing used: (1) all good quality cocoons/shells from on fresh mulberry leaves, being slightly higher the replicate were weighted and after that during the all instars and cocooning. divided by their number; (2) a random sample In regards to the different instars, the rearing consisting of 30 female and 30 male good temperature when artificial diet is used, is quality cocoons/shells was taken and after recommended to be kept higher (compared to weighting the weight is divided by the number. rearing on mulberry leaves only): such as 29 to For shell percentage determination, the ratio 30°C in the first and the second instars, 27 to between the weight of cocoon shell and the 28°C in the third instar, and 26°C in the fourth weight of fresh cocoon was used. The filament instar. It is assumed that at a high temperature length was determined on a random sample of larva might gain more weight than at a low 30 good quality cocoons after single cocoon temperature. In the fifth instar however, there is reeling test. also a difference (24°C for artificial diet-fed rearing) but it is still comparable with the RESULTS AND DISCUSSIONS temperature established for rearing on mulberry leaves only (20- 25°C). The fresh cocoon weight has a direct effect on In regards to the relative humidity, it can be seen the yield of the cocoon and also on the filament from Table 1 that the required interval is about length. 50 - 85%. Lowering this parameter is not The results in Table 2 show that we have the recommended as it can cause at least drying of highest values for the references of both strains the diet. Only daylight is applied during the in September 2017 and 2018. incubation (no artificial light) and thus 12 hours The variation of the characters in silkworms fed light and 12-hours dark rhythm is established. on artificial diet ranges from 0.55 to 1.52. The The “mass” hatching is observed on the 12th day lowest average values of the character were after the incubation has started and then the observed in July of 2017 in both the Svila 1 and larvae can be fed with artificial diet for first Svila 2. time.

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