Effect of cage size on Aedes albopictus wing length, survival and egg production

Developmental and Nutritional Dynamics of Malpighian Tubule Autofluorescence in the Asian Tiger Mosquito Aedes albopictus

Malpighian tubules (MTs) are arthropod excretory organs crucial for the osmoregulation, detoxification and excretion of xenobiotics and metabolic wastes, which include tryptophan degradation products along the kynurenine (KYN) pathway. Specifically, the toxic intermediate 3-hydroxy kynurenine (3-HK) is metabolized through transamination to xanthurenic acid or in the synthesis of ommochrome pigments. Early investigations in Drosophila larval fat bodies revealed an intracellular autofluorescence (AF) that depended on tryptophan administration. Subsequent observations documented AF changes in the MTs of Drosophila eye-color mutants genetically affecting the conversion of tryptophan to KYN or 3-HK and the intracellular availability of zinc ions. In the present study, the AF properties of the MTs in the Asian tiger mosquito, Aedes albopictus, were characterized in different stages of the insect's life cycle, tryptophan-administered larvae and blood-fed adult females. Confocal imaging and microspectroscopy showed AF changes in the distribution of intracellular, brilliant granules and in the emission spectral shape and amplitude between the proximal and distal segments of MTs across the different samples. The findings suggest AF can serve as a promising marker for investigating the functional status of MTs in response to metabolic alterations, contributing to the use of MTs as a potential research model in biomedicine.

Investigation on key aspects of mating biology in the mosquito Aedes koreicus

Aedes koreicus Edwards, 1917 (Hulecoetomyia koreica) is a mosquito (Diptera: Culicidae) from Northeast Asia with a rapidly expanding presence outside its original native range. Over the years, the species has been discovered in several new countries, either spreading after first introduction or remaining localised to limited areas. Notably, recent studies have demonstrated the ability of the species to transmit zoonotic parasites and viruses both in the field and in laboratory settings. Combined with its invasive potential, the possible role of Ae. koreicus in pathogen transmission highlights the public health risks resulting from its invasion. In this study, we used a recently established population from Italy to investigate aspects of biology that influence reproductive success in Ae. koreicus: autogeny, mating behaviour, mating disruption by the sympatric invasive species Aedes albopictus Skuse, 1894, and the presence of the endosymbiont Wolbachia pipientis Hertig, 1936. Our laboratory population did not exhibit autogenic behaviour and required a bloodmeal to complete its ovarian cycle. When we exposed Ae. koreicus females to males of Ae. albopictus, we observed repeated attempts at insemination and an aggressive, disruptive mating behaviour initiated by male Ae. albopictus. Despite this, no sperm was identified in Ae. koreicus spermathecae. Wolbachia, an endosymbiotic bacterium capable of influencing mosquito reproductive behaviour, was not detected in this Ae. koreicus population and, therefore, had no effect on Ae. koreicus reproduction.

Aedes albopictus microbiota: Differences between wild and mass-reared immatures do not suggest negative impacts from a diet based on black soldier fly larvae and fish food

The "Sterile Insect Technique" (SIT), a promising method to control Aedes albopictus, the Asian tiger mosquito, is gaining increasing interest. Recently, the role of microbiota in mosquito fitness received attention, but the link between microbiota and larval diet in mass rearing programs for SIT remains largely unexplored. We characterized the microbiota of four larval instars, pupae and eggs of non-wild (NW) lab-reared Ae. albopictus fed with a diet based on Black soldier fly (Hermetia illucens) larvae powder and fish food KOI pellets. We compared it with wild (W) field-collected individuals and the bacterial community occurring in rearing water-diet (DIET). A total of 18 bacterial classes with > 0.10% abundance were found overall in the samples, with seven classes being especially abundant. Overall, the microbiota profile significantly differed among NW, W and DIET. Verrucomicrobiae were significantly more abundant in W and DIET, Bacteroidia were more abundant in NW and DIET, and Gammaproteobacteria were only more abundant in W than in DIET. W-eggs microbiota differed from all the other groups. Large differences also appeared at the bacterial genus-level, with the abundance of 14 genera differing among groups. Three ASVs of Acinetobacter, known to have positive effects on tiger mosquitoes, were more abundant in NW than in W, while Serratia, known to have negative or neutral effects on another Aedes species, was less abundant in NW than in W. The bacterial community of W-eggs was the richest in species, while dominance and diversity did not differ among groups. Our data show that the diet based on Black soldier fly powder and fish food KOI influences the microbiota of NW tiger mosquito immature stages, but not in a way that may suggest a negative impact on their quality in SIT programs.

Characterization of Spontaneous Melanization by Fluorescence Spectroscopy: A Basis for Analytical Application to Biological Substrates

Melanin is present in various biological substrates where it may participate in several processes, from innate immunity to the still-unsolved opposite roles in antioxidant protection, including photoprotection and the related ability to interact with light. Melanin–light interaction has also been an important source of inspiration for the development of innovative bioengineering applications. These are based on melanin’s light-energy-absorption ability of its chemically and structurally complex components and precursors, and on the improvement in analytical and diagnostic procedures in biomedicine. In this regard, here, we characterized the fluorescence spectral properties of melanin and of its precursor L-tyrosine in an aqueous solution during spontaneous melanization. Besides the confirmation of the typical fluorescence-emission signature of melanin and L-tyrosine, we provide additional insights on both emission and excitation spectra recorded during melanization. On these bases, we performed a subsequent characterization on the aqueous extracts from two different melanin-containing biological substrates, namely hairs from a domestic black cat and eggs from the Asian tiger mosquito. The results from the mild extraction procedure, purposely applied to obtain only the soluble components, combined with fluorescence spectral analysis are expected to promote further investigation of the melanization processes, particularly in insects.

Aedes albopictus Sterile Male Production: Influence of Strains, Larval Diet and Mechanical Sexing Tools

The sterile insect technique (SIT) is a biologically based method of pest control, which relies on the mass production, sterilization, and release of sterile males of the target species. Since females can transmit viruses, it is important to develop a mass rearing system to produce a large number of males with a low presence of females. We evaluated the effects of different strains, larval diets and sexing tools on male productivity and residual female presence for the application of SIT against Aedes albopictus. Strains coming from Italy, Germany, Greece, and Montenegro, with different levels of colonization, were reared with three larval diets: IAEA-BY, BLP-B and SLP-BY. Developed pupae were sexed using two different mechanical methods: sieve or Fay-Morlan separator. The results proved that adoption of the Fay-Morlan separator increased the productivity and limited the female presence. The IAEA-BY diet showed the lowest female contamination. Strains with a high number of breeding generations showed a decreased productivity and an increased female presence. Increased female presence was found only in extensively reared strains and only when the sorting operation was conducted with sieves. We hypothesize that extensive colonization may determine a size reduction which limits the sexing tool efficiency itself.