Towards a Rational Basis for the Selection of Probiotics to Improve Silkworm Health and Performance

Pathogenic infections of silkworms constitute the greatest threat to sericulture. An attractive approach to the improvement in silkworm health and performance comprises the use of probiotics, i.e., microorganisms that confer beneficial properties such as an increased growth rate and resistance against pathogens. While this method has already resulted in promising results, generally, there is a lack of a rational basis for guidance on the selection of probiotics. This review attempts to organize useful information that needs to be considered for the successful application of probiotics: the constitution of the microbiota in silkworms and its origins; the interaction of the major silkworm pathogens with the microbiota; and the microorganisms that have been used so far as silkworm probiotics. Our analysis points to two major issues that seem of vital importance: (1) the absence of a "core microbiota" in silkworms which necessitates continuous supply of beneficial microorganisms according to environmental conditions and (2) the apparent negative impact that some other microorganisms can have on resistance against baculovirus infections. Recent findings have reported the beneficial effects of lactic acid bacteria (Lactobacillus sp.) when applied as probiotics in improving silkworm health and performance.