Margaret Keister

Respiration of phormia regina in relation to temperature and oxygen

Abstract Respiratory rates of larvae, pupae, and adults of Phormia regina in general follow a sigmoid curve with respect to temperatures from 0 to 45°C. One exception is an unexplained plateau between 10 and 15° in the curve for intact larvae. At 25° respiration of larvae and pupae is somewhat more dependent on ambient O2 concentration than that of adults, the dependence of the former being limited at concentrations between 10 and 15%, and the latter at concentrations below 5%. The contributions of ‘resting’ and ‘activity’ respiration with respect to temperature and O2 concentration are evaluated by comparing deganglionated larvae and headless flies with intact ones. The role of spiracular area as a respiration-limiting factor is explored in experiments with artificially enlarged larval spiracles. The bearing of this work on the mechanism of gas transfer in insects is briefly considered.

Cyclic CO2 release in diapausing pupae—II: Tracheal anatomy, volume and pCO2; Blood volume; Interburst CO2 release rate

An average one gram cyclically-respiring diapausing pupa of the saturniid moth Agapema galbina has a tracheal volume of about 60 μl and a tracheal pCO2 of 45 mm Hg. This shows that nearly 90 per cent of the approximately 30 μl of gaseous CO2 released during a “burst” must come out of solution and combination in tissue stores. Body water per g is distributed: blood, 330 μl; tissues, 180 μl; gut lumen, 100 μl; and cuticle 110 μl. Dimensions of the major parts of the tracheal path from environment to tissues are given, and it is shown by computation that the spiracular valve is the only site where significant resistance to diffusion could occur. It is shown statistically that the rate of CO2 release increases gradually during the interburst period, as it should if CO2 is being impounded in body buffers. Arguments are advanced for cyclic CO2 release being potentially widespread in insects under conditions where O2 supply is high relative to demand.

Tracheal filling in Sciara larvae.

(1) After each molt the new tracheal system of a Sciara larva in air normally remains filled with liquid for 3 to 8 minutes. It then fills spontaneously, rapidly and completely with gas, beginning at some point in a main trunk. The gas comes from some internal source.(2) Sciara larvae can molt under aerated water, and can fill their tracheal systems with gas while completely submerged in aerated or boiled water, or mineral oil.(3) Tracheal filling can occur if the larva is in a mixture of 99.7 per cent CO2, CO or N2 with 0.3 per cent O2, but not in complete absence of O2.(4) Tracheal filling is indefinitely inhibited near 0° C.(5) Filling may be stopped and restarted repeatedly by alternating exposures to anoxic gas and air, or to low and room temperatures.(6) Initiation and progress of tracheal filling are apparently independent of body movements, body hydrostatic pressure, and critical gas ratios.(7) It is suggested tentatively that tracheal filling involves a metabolic process.(8) A review and critique...

Diffusion Phenomena in the Tracheae of Phormia Larvae

I N STUDYING the cutaneous respiration of larvae of Phormia regina, we observed that larvae submerged for 6 hours in oxygenated water and then returned to air were at first able to move about but died within a few hours, while those submerged for 6 hours in aerated water and then returned to air showed at first no pulse, intestinal peristalsis, or body movement but eventually recovbags were exposed to a gas or submerged in water saturated with the gas. They were then removed at intervals and examined with a dissecting microscope. In other experiments we used the arrangement pictured in Figure 1, in which larvae were induced to crawl serially into a glass tube of bore slightly greater than the larval diameter and were separated by screen-ended spools. Three such larvae could be conveniently kept under ob-

An areal method for calibrating microburettes

Abstract At a given temperature and humidity the areas of spots produced on filter paper by minute droplets of dye solution are related exponentially to the corresponding volumes. Areal calibration can be used to check the linearity of delivery of microburettes and microinjection syringe systems, and to estimate the variation between repeated deliveries of volumes as small as 0.1 ml. Bei einer bestimmten Temperatur und Feuchtigkeit sind die von sehr kleinen Tropfen einer Farbelosung auf Filterpapier hinterlassenen Flecke, den entsprechenden Volumina exponentiell proportional. Diese Kalibriermethode kann benutzt werden, um die Regelmassigkeit des Ausflusses von Mikroburetten und Mikroinjektionsspritzen zu kontrollieren und die Volumanderungen bis zu 0.1 ml zu verfolgen.