Diel rhythm of volatile emissions of males and females of the peach fruit fly Bactrocera zonata.

Fruit flies in the genus Bactrocera are among the most destructive insect pests of fruits and vegetables throughout the world. A number of studies have identified volatiles from fruit flies, but few reports have demonstrated behavioral effects or sensitivities of fly antennae to these compounds. We applied a recently developed method of automated headspace analysis using SPME (Solid Phase Microextraction) fibers and GC-MS (gas chromatography mass spectrometry), termed SSGA, to reveal volatiles specific to each sex of B. zonata that are emitted in a diel periodicity. The volatiles released primarily at dusk were identified by GC-MS and chemical syntheses as several spiroacetals, pyrazines, and ethyl esters. Solvent extraction of male rectal glands or airborne collections from each sex, followed by GC-MS, showed that certain of the volatiles increase or decrease in quantity sex-specifically with age of the flies. Electroantennographic (EAG) analysis of dose-response indicates differences in sensitivities of male and female antenna to the various volatiles. Our study provides a comprehensive analysis of the volatile chemicals produced and released by B. zonata and their antennal responses. The possible pheromone and semiochemical roles of the various volatiles released by each sex and the difficulties of establishing behavioral functions are discussed.

Thermal death kinetics of egg and third instar Mediterranean fruit fly (Diptera: Tephritidae).

Two developmental stages of Ceratitis capitata (Wiedemann), 24-h-old eggs and third instars, 8 d after oviposition, were subjected to thermal exposures in a heating block system, at various temperatures of 46, 48, 50, and 52 degrees C to determine the thermal death kinetics of the insects. At these temperatures, 100% mortality was achieved by exposure of 300 C. capitata larvae for 60, 15, 4, and 1 min, respectively. The 0.5 order kinetic model had the best fit to the survival ratio for all the treatment temperatures, hence it was used for the prediction of the lethal times. The thermal death time (TDT) curves showed that the third instars were more heat-resistant than eggs, especially at the two low temperatures (46 and 48 degrees C). Under temperature-time combinations that did not result in complete kill, the thermal mortality for eggs was also significantly higher than that for third instars. The activation energy values calculated from the TDT curves were 490.6 and 551.9 kJ/mol, respectively, for thermal death of eggs and third instars.

Fractal characteristics of tumor vascular architecture during tumor growth and regression.

OBJECTIVE: Tumor vascular networks are different from normal vascular networks, but the mechanisms underlying these differences are not known. Understanding these mechanisms may be the key to improving the efficacy of treatment of solid tumors. METHODS: We studied the fractal characteristics of two-dimensional normal and tumor vascular networks grown in a murine dorsal chamber preparation and imaged with an intravital microscopy station. RESULTS: During tumor growth and regression, the vasculature in the tumor has scaling characteristics that reflect the changing state of the tissue. Growing tumors show vascular networks that progressively deviate from their normal pattern, in which they seem to follow diffusion-limited aggregation to a pathological condition in which they display scaling similar to percolation clusters near the percolation threshold. The percolation-like scaling indicates that the key determinants of tumor vascular architecture are local substrate properties rather than gradients of a diffusing substance such as an angiogenic growth factor. During tumor regression the fractal characteristics of the vasculature return to an intermediate between those of growing tumors and those of healthy tissues. Previous studies have shown that percolation-like scaling generally inhibits transport. CONCLUSIONS: In the present context, the percolation-like nature of tumor vasculature implies that tumor vascular networks possess inherent architectural obstacles to the delivery of diffusible substances such as oxygen and drugs.

Role of tumor vascular architecture in nutrient and drug delivery: an invasion percolation-based network model.

Delivery of diffusible nutrients and drugs in tissues is limited in part by the distance over which substances must diffuse between the vascular space and the surrounding tissues and by upstream losses prior to local delivery by the blood. By examining the fractal behavior of two-dimensional vascular networks in the murine dorsal skinfold chamber preparation, we have identified distinct architectural features of normal and tumor vascular networks that lead to fundamentally different transport behavior. Normal capillaries which are relatively straight and regularly spaced are well modeled by the widely used Krogh cylinder model. In contrast, the fractal dimensions of tumor vascular networks suggest that the tortuous vessels and wide range of avascular spaces found in tumors are better represented by invasion percolation, a well-known statistical growth process governed by local substrate properties. Based on these observations, we have constructed a percolation-based model of tumor vascular growth that enables us to predict the effects of network architecture on transport. We find that the number of avascular spaces in tumors scales with the size of the spaces so that there will exist a few large avascular spaces and many smaller avascular spaces between vessels. We also find that the tortuosity of the vessels, as reflected by the elevated minimum path dimension, produces regions of locally flow-limited transport and reduces flow through the tumor as a whole. Our model helps to explain the long-standing paradox that tumor vasculature has a higher geometrical resistance than normal vasculature despite increases in vessel diameter. A comparison to oxygenation measurements in normal and tumor tissues shows that our model predicts the architectural obstacles to transport in tumors more accurately than the Krogh cylinder model. Our results suggest that clinical interventions that yield more regular vascular geometry may be useful as a supplement to those that improve arterial availability or decrease rates of consumption by the tissue.

Immunochemical and biological analysis of pheromone biosynthesis activating neuropeptide in Heliothis peltigera.

This study describes the preparation and characterization of a highly specific antiserum to Helicoverpa zea pheromone biosynthesis activating neuropeptide (Hez-PBAN), and the use of this antiserum, in an enzyme linked immunosorbent assay (ELISA), to determine: a) the content of endogenous PBAN in head extracts of male and female Heliothis peltigera; b) the level of PBAN at different developmental stages; and c) the content of PBAN in four different moth species. Cross-reactivity studies revealed that the antiserum is directed mainly toward the N-terminal region of the neuropeptide, and that it exhibits similar binding affinities toward the oxidized and reduced forms of PBAN. Analysis of PBAN content in head extracts of male and female H. peltigera, at scotophase, revealed the presence of 4.97 and 4.58 pmol, respectively, in 3-day-old moths, and 5.33 and 4.78 pmol, respectively, in 7-day-old moths. The similarity in the content of PBAN at both ages and sexes was in accordance with the amount of pheromonotropic activity in these extracts which stimulated pheromone biosynthesis to a similar level. Analysis of PBAN-like immunoreactivity (IR) in head extracts of H. peltigera larvae and pupae demonstrated the existence of the neuropeptide in the 4th larval instar and continued to increase as a function of development. No IR could be detected in the first three larval instars. The larval and pupal extracts also exerted pheromonotropic activity which followed a similar pattern. The activity in these extracts, however, was considerably lower than that found in adult male and female heads. IR was also detected in head extracts of three other Noctuidae moths: Helicoverpa armigera, Cornutiplusia circumflexa and Spodoptera littoralis, indicating a high degree of chemical and structural similarity of PBAN in these moths.