Viability of Culex pipiens pipiens eggs affected by nutrition and aposymbiosis

Raisins were a better source of carbohydrate than sucrose for reproduction by autogenous Culex pipiens. A blood meal increased the number of eggs per raft from 49 autogenously to 114. Eggs of aposymbiotic females produced autogenously did not hatch, but 34% of the eggs were viable if the mosquitoes fed on chickens. With repeated blood meals the number of eggs per raft and the rate of embryonation and hatching declined in each successive gonotrophic cycle. In about $\text{1}\text{4}$ of the unhatched eggs of normal females there were no fully developed embryos, while many more of the unhatched eggs of aposymbiotic females contained no evidence of embryonic development. After the fifth blood meal, neither normal nor aposymbiotic insects oviposited. The ovaries of the nulliparous females contained approximately 10% of the potential number of mature terminal oocytes. Proximally in the ovarioles there were dilatations and coiled tracheoles indicating egg resorption. There were fewer parous follicles in aposymbiotic than in normal females. Larval rearing water, i.e., infusion in which larvae had been reared, was more attractive than fresh infusion for oviposition by normal, autogenous mosquitoes. The degree of embryonation of the eggs was lower and the hatching success rate was poorer in fresh infusion than in larval rearing water.     

Effect of photoperiod and temperature on ovarian development in Culex pipiens pipiens

Culex pipiens pipiens is one member of the C. pipiens complex which diapauses as an adult. Experiments show that photoperiod and temperature both affect the development of the ovarian follicles. Females reared at a 15 hr photophase and 22°C show an increase in follicle size over the first 8 days after emergence. Females reared at 10 hr and 22°C do not show an increase in follicle size. Follicle size does not gradually increase as photophase is lengthened. Rather, at photophases between 9 and 12 hr the follicles remain small and at photophases of 13 hr or more, the increase is seen. An increase in temperature tends to increase follicle size regardless of the photophase. However, a strong interaction between photophase and temperature is evident.No evidence exists for a single ‘critical stage’. Instead, the final follicle size is dependent, in a complex manner, upon the photophase experienced by all the stages. The final size is not a result of a cumulative effect.Photoperiod, independent of temperature, shows a marked effect on blood feeding. Females reared at 15 hr feed much more readily than those reared at 10 hr. Those 10 hr females that feed show no signs of gonotrophic dissociation.     

Esterase polymorphism and sensitivity to dursban organophosphorus insecticide in Culex pipiens pipiens populations

Esterase polymorphism and Dursban (O,O-dimethyl-2-pyridylphosphorothioate) sensitivity have been investigated in 12 natural populations and three laboratory strains of Culex pipiens pipiens. This mosquito has two esterase loci, Est-1 and Est-2, which were shown to code esterases of the B group (aliesterases) but not cholinesterases. No correlation between Est-1 polymorphism and Dursban sensitivity was found, but the increase of the Est-2(0.64) allele in the populations less sensitive to Dursban was highly significant (r = -0.9850 for 6 df).     

Midgut barrier imparts selective resistance to filarial worm infection in Culex pipiens pipiens

Mosquitoes in the Culex pipiens complex thrive in temperate and tropical regions worldwide, and serve as efficient vectors of Bancroftian lymphatic filariasis (LF) caused by Wuchereria bancrofti in Asia, Africa, the West Indies, South America, and Micronesia. However, members of this mosquito complex do not act as natural vectors for Brugian LF caused by Brugia malayi, or for the cat parasite B. pahangi, despite their presence in South Asia where these parasites are endemic. Previous work with the Iowa strain of Culex pipiens pipiens demonstrates that it is equally susceptible to W. bancrofti as is the natural Cx. p. pipiens vector in the Nile Delta, however it is refractory to infection with Brugia spp. Here we report that the infectivity barrier for Brugia spp. in Cx. p. pipiens is the mosquito midgut, which inflicts internal and lethal damage to ingested microfilariae. Following per os Brugia exposures, the prevalence of infection is significantly lower in Cx. p. pipiens compared to susceptible mosquito controls, and differs between parasite species with <50% and <5% of Cx. p. pipiens becoming infected with B. pahangi and B. malayi, respectively. When Brugia spp. mf were inoculated intrathoracically to bypass the midgut, larvae developed equally well as in controls, indicating that, beyond the midgut, Cx. p. pipiens is physiologically compatible with Brugia spp. Mf isolated from Cx. p. pipiens midguts exhibited compromised motility, and unlike mf derived from blood or isolated from the midguts of Ae. aegypti, failed to develop when inoculated intrathoracically into susceptible mosquitoes. Together these data strongly support the role of the midgut as the primary infection barrier for Brugia spp. in Cx. p. pipiens. Examination of parasites recovered from the Cx. p. pipiens midgut by vital staining, and those exsheathed with papain, suggest that the damage inflicted by the midgut is subcuticular and disrupts internal tissues. Microscopic studies of these worms reveal compromised motility and sharp bends in the body; and ultrastructurally the presence of many fluid or carbohydrate-filled vacuoles in the hypodermis, body wall, and nuclear column. Incubation of Brugia mf with Cx. p. pipiens midgut extracts produces similar internal damage phenotypes; indicating that the Cx. p. pipiens midgut factor(s) that damage mf in vivo are soluble and stable in physiological buffer, and inflict damage on mf in vitro.     

Cytodifferentiation in theRana pipiens oocyte

Summary This communication is concerned with an analysis of details in the morphogenesis of intramitochondrial yolk in oocytes of immatureRana pipiens, at different times during the prolonged diplotene stage of meiotic prophase in adult females, in fully-grown oocytes, and in those eggs artifically activated during early cleavage. The fine structure of the germinal cytoplasm of cleaving eggs is also characterized. The observations reported are discussed in relation to results obtained by others and in terms of current views regarding mitochondrial function. This investigation was supported by a research grant from the National Science Foundation.     

Observations on Mexican Rana pipiens

Mexican Rana pipiens now commonly sold in the United Statesdiffer morphologically and physiologically from their northerncounterparts. They resemble Arizona pipiens in appearance andbehavior, but their breeding cycle is distinctive. They aremost reproductively active in July and August. During late springand summer they can be ovulated readily and their pituitarygonadotropin levels are apparently high. Such is not the caseduring other times of the year. The role of Mexican frogs inteaching and research is discussed.     

Directionality of the pressure-difference receiver ears in the northern leopard frog, Rana pipiens pipiens

We studied the directional response of the coupled-eardrum system in the northern leopard frog, Rana pipiens pipiens. Eardrum behavior closely approximates a linear time-invariant system, with a highly correlated input–output relationship between the eardrum pressure difference and the eardrum velocity. Variations in the eardrum transfer function at frequencies below 800 Hz indicate the existence of an extratympanic sound transmission pathway which can interfere with eardrum motions. The eardrum velocity was shown to shift in phase as a function of sound incident angle, which was a direct result of the phase-shift of the eardrum pressure difference. We used two laser-Doppler vibrometers to measure the interaural vibration time difference (IVTD) and the interaural vibration amplitude difference (IVAD) between the motions of the two eardrums. The coupled-eardrum system enhanced the IVTD and IVAD by a factor of 3 and 3 dB, respectively, when compared to an isolated-eardrum system of the same size. Our findings are consistent with the time-delay sensitivity of other coupled-eardrum systems such as those found in crickets and flies.     

Directionality of phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens

Summary A dorsal approach to the eighth nerve and free-field stimulation were used to investigate the effect of sound direction and intensity on phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens.Tuning curves of 75 auditory neurons were analyzed (Fig. 2). Amphibian papillar neurons, but not basilar papillar neurons, exhibit significant phase locking to short tone bursts at the characteristic frequency (CF), the degree of phase locking (vector strength) decreasing with the neuron's CF (Figs. 3, 4 and 10E). Vector strength increases with sound pressure level to saturate about 20 dB above threshold, while the preferred firing phase is only slightly affected (Figs. 5 and 6).In contrast, sound direction hardly affects vector strength (Figs. 7, 8, 9A and 10A and C), but has a strong influence on the preferred firing phase (Figs. 7, 8, 9B and C, 10B and D): With respect to anterior tone presentation there are phase lags for ipsilateral and phase leads for posterior and contralateral presentation. Phase differences between both ears show a sinusoidal or cardioid/ovoidal directional characteristic; maximum differences are found with antero-lateral tone presentation (Fig. 11). The directionality of phase locking decreases with the neuron's CF (Fig. 10F) and only slightly changes with sound pressure level (Fig. 12). Thus, phase locking of amphibian papilla neurons can potentially provide intensity-independent information for sound localization.Abbreviations SPL sound pressure level - FTC frequency threshold curve - CF characteristic frequency - TF test frequency - VS vector strength - AP amphibian papilla - BP basilar papilla     

Morphology of neurons in the torus semicircularis of the northern leopard frog,Rana pipiens pipiens

The neuronal morphology of the torus semicircularis of the northern leopard frog, Rana pipiens pipiens, was examined in Golgi-impregnated material. Neurons in each of the five subdivisions of the torus semicircularis (Potter, '65a) have distinct morphologies which are characteristic of the subdivision. Laminar nucleus neurons are mostly multipolar with spherical or ovoidal somata and smooth dendrites oriented primarily parallel and perpendicular to the cell laminae. Principal nucleus neurons have variable soma shapes with short dendrites ( < 100 μm) radiating in all directions. In the magnocellular nucleus, there are three major cell types: neurons characterized by small, spherical-shaped somata, with short, thin, radiating dendrites and many varicosities; bi- or tripolar neurons with ovoidal somata, and long (100–200 μm) and smooth dendrites orienting primarily dorsoventrally and mediolaterally; and multipolar neurons with triangular-shaped somata and very long (200–350 μm) dendrites, which are either smooth or highly spiny. Neurons in the commissural nucleus are mostly multipolar cells with ovoidal somata and beaded dendrites projecting mostly dorsally and ventrally. The subependymal midline nucleus contains mostly uni- or bipolar neurons with small ovoidal somata and straight, spiny dendrites. In addition to revealing the morphological features of neurons in the torus, the counterstained material shows further cytoarchitectural organization of the principal nucleus, i.e., the presence of a circular lamellar organization. The functional significance of these anatomical features is discussed.     

Surface properties of Culex pipiens pipiens eggs and the behaviour of the female during egg-raft assembly

ABSTRACT. Eggs of the mosquito Culex pipiens pipiens L. float vertically because a flexible corolla at the anterior (lower) pole has a hydrophilic lower surface and a hydrofuge upper surface. The corolla assumes different configurations in the egg raft; the surface forces operating on eggs are briefly analysed. The outer surface of the chorion is hydrofuge, but in eggs floating on water there is a jacket of water surrounding the egg in the spaces between the tubercles of the exochorion, below the meshwork connecting them. The humidity over natural water can be low enough to cause continuous evaporation from the jacket; water is replenished through openings within the lower surface of the corolla. The disposition of the corolla prevents the uptake of materials confined to the water surface outside, but the mechanism could concentrate solutes in the jacket, with possible deleterious consequences. Eggs are joined together by inter-digitation of the regularly spaced tubercles. The behaviour by which the female assembles the egg raft is described in detail, explaining the form of the raft and the patterns in which eggs are packed.     

Cytodifferentiation in the Rana pipiens oocyte

Summary In early diplotene frog oocytes incubated to illustrate thiamine pyrophosphatase (TPPase) activity, reaction product is uniformly distributed within the compartments of the endoplasmic reticulum and nuclear envelope as well as within the saccules and small vesicles comprising the dictyosomes. With continued oocyte development the reaction product becomes concentrated in localized regions of the dictyosome saccules. Eventually, the enzyme is no longer apparent within the endoplasmic reticulum, but is concentrated in the cisternae of the inner dictyosome saccules. The variations noted suggest that the enzyme is synthesized early in diplotene by the endoplasmic reticulum and is subsequently transported to the Golgi apparatus where it is consistently observed at later developmental stages. TPPase activity is also present in the Golgi apparatus of follicle and theca cells as well as in ovarian epithelial cells. The enzyme is also detected in micropinocytotic vesicles contained within the cells comprising the follicle envelope and in intercellular spaces of the follicle. Horseradish peroxidase injected into the coelomic cavity is transported via micropinocytotic vesicles into and through the cells comprising the follicle envelope and in intercellular spaces. The exogenous protein is not found even after a prolonged time period in early diplotene oocytes. The protein is, however, present in large spherical and tubular vesicles in the cortex of vitellogenic oocytes approximately 500 microns in diameter. The possible functional role of the enzyme TPPase during oogenesis is discussed.This investigation was supported by a research grant from the National Science Foundation (GB-8736).     

The ultimobranchial body in Rana pipiens

Summary Autoplastic transplants of ultimobranchial glands of male Rana pipiens were bilaterally or unilaterally placed in a homeotopic or heterotopic site. Serum calcium levels were maintained at normal values in bilateral autotransplants, while total ultimobranchialectomy resulted in hypercalcemia. Electron microscopy verified the viability and functional state of transplanted, denervated glands. During the periods of denervation, ergastoplasm and Golgi membranes exhibited hypertrophy which was reversed when unmyelinated nerves reappeared in the pericapillary space. Autotransplants under hypercalcemic conditions indicated that the process of secretion is primarily an intrinsic cellular activity and independant of innervation. The present evidence suggests that the sympathetic axons which innervate the parenchyma probably are inhibitory in nature and may allow depression of glandular functions during periods of hypercalcemia.The technical assistance of Mrs. Lilly Weeks is gratefully acknowledged. This project was supported by N. I. H. Grant No. AM-11795; The National Institutes of Arthritic and Metabolic Diseases.