Alejandro Rabossi

Lipid, Carbohydrates and Protein Patterns During Metamorphosis of the Mediterranean Fruit Fly, Ceratitis capitata (Diptera: Tephritidae)

Abstract We investigated the patterns of total lipid, glycogen, hemolymph carbohydrate, and trichloroacetic acid-precipitable protein contents starting 8 h before puparium formation and throughout the whole metamorphosis of the Medfly, Ceratitis capitata (Wiedemann). In addition, during the early stages of metamorphosis, we measured the activity of acid proteinases and glutamate dehydrogenase (GDH), an important enzymatic link between amino acids and the tricarboxylic acid cycle. Lipids accumulate during the larval-dispersal phase and the first 20 h of the prepupal stage. Thereafter, levels decline slightly throughout the pupal stage and first half of the pharate-adult stage, and drastically decline toward the last hours of metamorphosis. Glycogen and hemolymph carbohydrates are highly used from the moment the larvae leave the diet until the mid-pupal stage, then glycogen increases toward the mid pharate-adult and decreases again to low levels at the moment of adult emergence. Protein levels decrease during the prepupal stage (coinciding with a rise in acid proteinase activity) recovering toward the pharate-adult stage. GDH activity increases during the prepupal stage, attaining maximal activity at the onset of the pupal stage and then declines to low levels. This high GDH activity may be linked to the conversion of glutamate to α-ketoglutarate while proteins are being broken during tissue histolysis. Our results are discussed in view of the differential utilization of metabolites during metamorphosis.

Photosensitizing effect of hematoporphyrin IX on immature stages of Ceratitis capitata (Diptera: Tephritidae).

Immature stages of Ceratitis capitata were tested as a model for hematoporphyrin IX (HP IX) phototoxicity. The lethal concentration 50 (LC50) of HP IX in the food was determined during postembryonic development until adult emergence as 0.173 mm (95% CI: 0.138–0.209). The corresponding HP IX LC50 during the dispersal period alone was 0.536 mm (95% CI: 0.450–0.633). HP IX toxicity was compared against Phloxine B (PhB) (0.5 mm). HP IX elicited a mortality of 90.87%, which was mainly concentrated during prepupal and early pupal stages. PhB mortality was much lower (56.88%) and occurred mainly during the adult pharate stage. A direct correlation between light‐dependent HP IX mortality, evidence of reactive oxygen species (ROS) and lipid peroxidation (conjugated dienes and thiobarbituric acid reactive substances) was established in C. capitata larvae. ROS were found to be very significant in both the brain and in the gut.

Lipid profiles as indicators of functional senescence in the medfly.

Changes associated with the age-related decline of physiological functions, and their relation with mortality rates, are thoroughly being investigated in the aging research field. We used the Mediterranean fruit fly Ceratitis capitata, largely studied by biodemographers, as a model for functional senescence studies. The aim of our work was to find novel combinatorial indicators able to reflect the functional state of adult insects, regardless of chronological age. We studied the profiles of neutral and polar lipids of head, thorax and abdomen of standard populations kept at 23 °C, at different ages. Lipid classes were separated by thin layer chromatography, and the quantitative values were used to find patterns of change using a multivariate principal component analysis approach. The lipid-dependent principal components obtained correlated with age, and differences between sexes were consistent with differences in the shape of the survival curves and the mortality parameters. These same components were able to discriminate populations with a behavioral decline due to a mild 28 °C thermal stress. Thus, young populations at 28 °C showed similar lipid profiles than old populations at 23 °C. The results indicated that the lipid-dependent components reflect the functional state of the flies, and so were named functional state components (FSCs). It is proposed that FSCs may be used as functional senescence indicators.

Extracellular activity of NBAD-synthase is responsible for colouration of brown spots in Ceratitis capitata wings

After the emergence of the Ceratitis capitata imago, the pale and folded wings are expanded and sclerotized to acquire the definitive form and to stabilize the cuticle. The wings of this fly show a specific pattern of brownish and black spots. Black spots are pigmented by melanin, whereas there was scarce information about the development of the brownish spots. N-beta-alanydopamine (NBAD) is the main tanning precursor in C. capitata body cuticle, and we hypothesized that it may be responsible for the colouration of the brownish spots. We determined the topology and timing of NBAD synthesis and deposition to attain the species-specific colouration pattern. We demonstrated that during the first hours the colour of the brownish spots was principally determined by the tanning of the hairs. Haemolymph circulation through the veins is required to tan the wings. We confirmed that soon after wing spreading, most of the wing epidermal cells disappeared. Thus, the tanning of the brown spots was accomplished when the wing lamina was devoid of cells. NBAD synthase (NBAD-S; Ebony protein in D. melanogaster) activity in wings was detected in pharate adults and lasted several days after the emergence, even after the end of the tanning process. This observation is in contrast to epidermal NBAD-S activity in the body, where it was nearly undetectable 48 h post emergence. Our results indicate that NBAD-S was exported and deposited into the extracellular matrix of the brown spot areas before cell death and that tanning occurs through gradual export of NBAD precursors (dopamine and b-alanine) from veins.

High chromosomal variation in wild horn fly Haematobiairritans (Linnaeus) (Diptera, Muscidae) populations.

Abstract The horn fly, Haematobia irritans is an obligate haematophagous cosmopolitan insect pest. The first reports of attacks on livestock by Haematobia irritans in Argentina and Uruguay occurred in 1991, and since 1993 it is considered an economically important pest. Knowledge on the genetic characteristics of the horn fly increases our understanding of the phenotypes resistant to insecticides that repeatedly develop in these insects. The karyotype of Haematobia irritans, as previously described using flies from an inbred colony, shows a chromosome complement of 2n=10 without heterochromosomes (sex chromosomes). In this study, we analyze for the first time the chromosome structure and variation of four wild populations of Haematobia irritans recently established in the Southern Cone of South America, collected in Argentina and Uruguay. In these wild type populations, we confirmed and characterized the previously published “standard” karyotype of 2n=10 without sex chromosomes; however, surprisingly a supernumerary element, called B-chromosome, was found in about half of mitotic preparations. The existence of statistically significant karyotypic diversity was demonstrated through the application of orcein staining, C-banding and H-banding. This study represents the first discovery and characterization of horn fly karyotypes with 2n=11 (2n=10+B). All spermatocytes analyzed showed 5 chromosome bivalents, and therefore, 2n=10 without an extra chromosome. Study of mitotic divisions showed that some chromosomal rearrangements affecting karyotype structure are maintained as polymorphisms, and multiple correspondence analyses demonstrated that genetic variation was not associated with geographic distribution. Because it was never observed during male meiosis, we hypothesize that B-chromosome is preferentially transmitted by females and that it might be related to sex determination.