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Industrial insect mass rearing aims to produce quality insects under safe sanitary conditions which can be compromised by pathogens and abiotic stressors. Therefore, knowledge on pathogen persistence, virulence and means of detection is of importance. This study focuses on the opportunistic pathogen <i>Serratia marcescens</i> (<i>Sm</i>) as a possible candidate to reveal sanitary issues in <i>Tenebrio molitor</i> (<i>Tm</i>) breeding. A screening test was performed to assess the impact of abiotic stressors (starvation, density and sieving) in presence and absence of <i>Sm</i>. Two <i>Sm</i> detection methods were conducted, and the kinetics of <i>Sm</i> persistence were investigated. Our results show that (i) the presence of <i>Sm</i> had a low but significant effect on <i>Tm</i> mortality, (ii) a short temporary starvation period had a negative impact on larval growth, (iii) the detection of <i>Sm</i> by q-PCR was sensitive but less convenient than a specific <i>Sm</i> growth media, (iv) the kinetics of persistence showed that <i>Sm</i> declined but survived for nine days in the feed and in the feces for three weeks. Both the relatively low virulence and the persistence in the environment suggest that <i>Sm</i> could be used as an indicator for the sanitary status of mealworm production.