In vitro and in vivo [14C]acetate incorporation during development of insects

Completion of metamorphosis after adult emergence in Ceratitis capitata (Diptera: Tephritidae)

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Two post-emergence phases were observed in medfly, a walking and a motionless phase.

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Main morphological events occurred during motionless phase.

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Definitive tanning of the wings is proposed as the end of C. capitata metamorphosis.

The ecdysis of the imago is a crucial step in the development of holometabolous insects. However, no information on several aspects of Ceratitis capitata imago emergence and subsequent body maturation is available. We analysed behavioural events and evaluated the oxygen consumption and the dynamics of carbohydrate and lipid reserves during puparium extrication and in newly emerged imago until full wing expansion. A system for recording images with the corresponding software for image analysis was built for this purpose. After extrication, C. capitata showed two early postemergence phases: walking (6.56 ± 4.01 min, 6.2% of the wing spreading period, WSP) and the phase without locomotor motion (98.75 ± 26.04 min; 93.8% WSP). Three main events were recognized during the last phase. The first involved an initial expansion of the wings (11.12 ± 4.32 min). The second event was the progressive tanning of the body cuticle in general and the wing veins in particular, and the last entailed the definitive expansion of the wings to attain the characteristic arrow-shaped wing aspect. Our studies here complement previous descriptions of the tanning process of newly emerged medfly adults (Pérez et al., 2018). As a consequence of the results presented here, we consider that the initial events of the newly emerged adult could be interpreted as the last steps of metamorphosis.

Coping with an unpredictable and stressful environment: the life history and metabolic response to variable food and host availability in a polyphagous tephritid fly

The way energy resources are used under variable environmental conditions lies at the heart of our understanding of resource management and opportunism in many organisms. Here we sought to determine how a time-limited, synovigenic and polyphagous insect with a high reproductive-potential (Anastrephaludens), copes behaviourally and metabolically with environmental unpredictability represented by constant and variable regimes of host availability and variation in food quality. We hypothesized that an adaptive response to a windfall of nutritious food would be the rapid accumulation of energy metabolites (whole body lipids, glycogen and proteins) in the female. We also studied patterns of oogenesis as an indicator of egg-reabsorption under stressful environmental conditions. As predicted, patterns of energy metabolites were mainly driven by the quality and temporal pattern of food availability. In contrast, patterns of host availability had a lower impact upon metabolites. When given constant access to high quality nutrients, after an initial increase early in life, whole body lipids and glycogen were regulated downward to a steady-state level and somatic protein levels did not vary. In contrast, when food uncertainty was introduced, whole body lipid, glycogen and protein oscillated sharply with peaks associated with pulses of high-quality food. Production of eggs was highest when offered continuous access to hosts and high quality food. Importantly, females fully recovered their reproductive capacity when fruit became available following a period of host deprivation. With no evidence of egg resorption and high levels of egg dumping, it appears that egg dumping may favour the continuous production of eggs such that the female's reproductive tissues are ready to respond to rapid changes in the availability of hosts. Our results exemplify the capacity of insects to maximize reproduction under variable and stressful environmental conditions.

Total body nitrogen and total body carbon as indicators of body protein and body lipids in the melon fly Bactrocera cucurbitae: effects of methoprene, a juvenile hormone analogue, and of diet supplementation with hydrolyzed yeast

The application of methoprene, and providing access to diet including hydrolyzed yeast, are treatments known to enhance mating success in the male melon fly Bactrocera cucurbitae Coquillett (Diptera: Tephritidae), supporting their use in mass rearing protocols for sterile males in the context of sterile insect technique (SIT) programmes. The objective of the present laboratory study was to investigate the effect of methoprene application and diet supplementation with hydrolyzed yeast (protein) on the turnover of body lipids and protein to confirm the feasibility of their application in melon fly SIT mass-rearing programmes. While females had access to a diet that included hydrolyzed yeast (protein), males were exposed to one of the following treatments: (1) topical application of methoprene and access to diet including protein (M+P+); (2) only diet including protein (M-P+); (3) only methoprene (M+P-) and (4) untreated, only sugar-fed, control males (M-P-). Total body carbon (TBC) and total body nitrogen (TBN) of flies were measured at regular intervals from emergence to 35 days of age for each of the different treatments. Nitrogen assimilation and turnover in the flies were measured using stable isotope ((15)N) dilution techniques. Hydrolyzed yeast incorporation into the diet significantly increased male body weight, TBC and TBN as compared to sugar-fed males. Females had significantly higher body weight, TBC and TBN as compared to all males. TBC and TBN showed age-dependent changes, increasing until the age of sexual maturity and decreasing afterwards in both sexes. Methoprene treatment did not significantly affect TBC or TBN. The progressive increase with age of TBC suggests that lipogenesis occurs in adult male B. cucurbitae, as is the case in other tephritids. Stable isotope dilution was shown to be an effective method for determining N uptake in B. cucurbitae. This technique was used to show that sugar-fed males rely solely on larval N reserves and that the N uptake rate in males with access to diet including hydrolyzed yeast was higher shortly after emergence and then stabilized. The implications of the results for SIT applications are discussed.

Neutral lipid composition of Culex quinquefasciatus and Culex tritaeniorhynchus cells at two phases of growth

The mosquito cells Culex quinquefasciatus and Culex tritaeniorhynchus were grown in spinner cultures. The fatty acid profiles of the neutral lipid classes were analyzed, and comparisons were made between the two species at logarithmic and stationary phases of growth and between the species and the medium. The results from the data suggest an increase in the average chain length of the fatty acids in the free fatty acid and sterol ester fractions of the Culex quinquefasciatus cells with aging. From the logarighmic to stationary phase, both Culex cells showed some increase in desaturation of acids in the di- and triglyceride and free fatty acid fractions. The Culex tritaeniorhynchus cells also showed some increase in desaturation of acids in the monoglyceride fraction. Differences between the two Culex species at the logarithmic phase of growth were observed in the fatty acid profiles of all the neutral lipid fractions examined and at the stationary phase of growth in the free fatty acid, triglyceride, and sterol ester fractions.

Comparison of phospholipid composition of Aedes aegypti and Aedes albopictus cells obtained from logarithmic and stationary phases of growth

Aedes aegypti and Aedes albopictus cells were grown in tissue culture and harvested at logarithmic and stationary phases of development. The phospholipids were extracted, separated into lipid classes, and fatty acid composition of each fraction determined. The phosphatidylethanolamine fraction was the major lipid (42-54%). With aging, the A. aegypti cells showed an increase in polyenes in the phosphatidylcholine and phosphatidylethanolamine fractions and in monoenes and polyenes in the phosphatidylinositol fraction. The lysophosphatidylcholine fraction had an increase in chain length of the fatty acids with aging of the A. aegypti cells. The A. albopictus cells, with aging, showed increases in chain length and in the relative percentage of polyenes in the lysophosphatidylcholine, phosphatidylcholine, and phosphatidylserine fractions. In the phosphatidylinositol fraction, chain elongation of fatty acids occurred as the cells aged. In the ceramide phosphorylcholine fraction, there were increases in saturation and chain elongation of the fatty acids from the logarithmic to the stationary phase of the A. albopictus cells. An increase in polyenes was observed with aging of the cells in the phosphatidylethanolamine fraction.

On methylating activity of L-(methyl-14C)-methionine in metabolism of phospholipids by insect Ceratitis capitata

The methylating activity of L-(methyl-14C)-methionine in different stages of developmenent of the insect Ceratitis capitata was studied in a series of in vitro and in vivo experiments. Larval and pharate adult homogenates of the insect were used in the in vitro conditions, and the utilization of the methyl group of methionine for the synthesis of different classes of phospholipids was evaluated. Incorporation of radioactivity in lipids by pharate adult homogenates was significantly higher than that by larval homogenates. In both cases, phosphatidyl ethanolamine showed the highest levels of radioactivity incorporation. Free bases from total lipid hydrolysates were resolved and identified by paper chromatography, and the labeling was investigated by radioactivity scanning of paper chromatograms. Significant differences were observed in the activity of both stages of development of the insect. Larval and pharate adult homogenates incorporated mainly the labeled methyl groups into ethanolamine. Monmethyl ethanolamine was the only methyl derivative that appeared in the hydrolysates of lipids synthesized by larval homogenates, whereas mono-,di-and trimethyl ethanolamine clearly were detected in those synthesized by pharate adult homogeneates. Administration of L-(methyl 14C)-methionine to larvae confirmed the existence of methylation reactions in the metabolic activity of the insect.