Insects with forensic and agri-food implicationsfannia pusio (Diptera: Fanniidae) and Tenebrio molitor (Coleoptera: Tenebrionidae)

Abstract

The information gathered in this thesis increases the knowledge of two species with different objectives in applied entomology. The results obtained in Part I provide information that highlights the potential usefulness of Fannia pusio (Wiedemann, 1830) in forensic entomology, while the results in Part II cover information on Tenebrio molitor (Linnaeus, 1758), a species recently approved for food purposes. This information will further the knowledge of insect biology, ecology and ethology for its application. Fannia is a genus of diptera belonging to the family Fanniidae with approximately 300 species; they are attracted to decaying organic matter and have a necrophagous habit, which sheds light on criminological issues. In addition to their legal importance, they are of medical and economic interest, as they are capable of causing myiasis in domestic animals and humans. For these reasons, a correct identification at species level must be carried out where molecular analysis is complemented by morphological studies. DNA barcoding uses a 658 bp fragment of the mitochondrial genome (cox1), but sometimes the sequences of this fragment can be contaminated with external DNA remnants; as an alternative, short, internal regions (mini-barcode) can be used. In this work we show the ability of a 240 bp fragment to correctly identify the species of the genus Fannia that were collected through sampling throughout the Iberian Peninsula. Molecular identification showed F. pusio as the most abundant species presenting particular mutations that allow us to differentiate haplotypes from north-eastern and south-eastern individuals. The sequences available in the databases analysed together with the results of this work suggest that the species originates from America and that it was subsequently introduced into the Iberian Peninsula via Portugal, undergoing a continuous expansion of its distribution area. Variation in the shape of a selection of body characters is assessed by Geometric Morphometry using the head as the innovative structure. Sex must be taken into account as a key covariate in such studies, since Fannia, like many other Diptera, has a sexually dimorphic head structure, with holoptic males and dichoptic females. Our analyses provide significant morphological information where F. pusio shows a clear intraspecific morphometric variation along an east-west axis throughout the Iberian Peninsula. A similar pattern was obtained from a laboratory-reared colony versus wild samples. The behavioural peculiarities of the insects may provide additional information for future research. The application of entomology in the forensic field has focused especially on the early colonising taxa of corpses in the initial phase of decomposition. However, species occurring at more advanced stages can contribute to further knowledge, as is the case of F. pusio. In addition, it has the ability to colonise buried corpses, a condition in which larger dipterans are unable to do so. In this work we study its behaviour in a temperature range from 5 ºC to 40 ºC, and the lengths of the different stages in order to calculate the post-mortem interval (PMI) using isomorphen and isomegalen diagrams. The results shown, together with the existing bibliography of other species, help to broaden the knowledge of the entomofauna occurring in forensic investigations. On the other hand, the yellow mealworm, or T. molitor, is a beetle of the family Tenebrionidae that has recently been accepted by the European Food Safety Agency as a food safe species. The increasing population and use of protein in animal feed make insects a prime candidate as a promising sustainable alternative due to their high protein, healthy fats and fibre content, and their low cost of production compared to conventional livestock. In this study we present a proposal for a T. molitor farm where optimal rearing conditions, management, calculation of annual production in the facilities and economic feasibility are analysed to determine the profitability of the project. Previously unknown anomalies are becoming more frequent with the rise of insect farms. In our facilities, incomplete development of metamorphosis has been observed, resulting in adults with malformations in the abdomen and elytra. Three of the genes involved in the metabolic pathway of sclerotization and melanisation (TH, AANAT1 and Lac2) are analysed by RT-qPCR, using a previously validated reference gene (Rps3), to determine the expression level of these genes. Abnormal individuals with the same malformation and normal individuals were chosen and used as controls and significant differences were observed.