Differential gene expression during metamorphosis: a promising approach for age estimation of forensically important Calliphora vicina pupae (Diptera: Calliphoridae)

Necrophagous blow fly larvae can provide accurate estimates of the minimum postmortem interval in death investigations. During larval development, predictable morphological changes occur and measurements of weight, length, and width are compared to species-specific growth curves for reliable age estimates. However, aging blow fly pupae is more challenging because morphological and anatomical changes are not visible with the naked eye. Thus, delicate preparation of the pupae or rearing to the adult stage seems unavoidable. Conversely, metamorphosis evokes a remodelling of the larval shape to adult structures, and gene expression analysis potentially serves as a molecular tool to mirror the ageing process of a pupa. The present study focuses on the differential expression of two newly described, arbitrarily named genes (15_2, 2014192) and two previously identified genes (actin, arylphorin receptor) during Calliphora vicina (Diptera: Calliphoridae) metamorphosis. Quantification through real-time PCR revealed significant up- and downregulation of these transcripts found to be temperature dependent and age specific, hence, a new possibility to age forensically important blow fly pupae.