Defense reactions of mosquitoes to filarial worms: potential mechanism for avoidance of the response by Brugia pahangi microfilariae

The melanization response of Aedes trivittatus and the black-eyed Liverpool (LVP) and Rocke-feller (RKF) strains of Aedes aegypti against intrathoracically inoculated Brugia pahangi microfilariae (mff) that previously had penetrated LVP, RKF, or A. trivittatus midguts in vitro was assessed at 1, 3, and 5 days postinoculation (PI). LVP and RKF midgut-derived mff almost totally avoided the melanization response and developed normally in LVP strain A. aegypti, and although over 90% of these mff died by 5 days PI in RKF mosquitoes, the majority of these were not melanized. A. aegypti midgut-derived mff also were able to avoid the response of A. trivittatus in 33–43% of the cases. Penetration through A. trivittatus midguts, however, did not significantly affect the ability of mff to avoid the melanization response in any of the mosquitoes examined. Allogeneic and xenogeneic tissue inplants were accepted by all three mosquito species examined. Data presented support the hypothesis that mff avoid immune recognition in compatible mosquitoes by coating themselves with midgut material(s) during penetration of the midgut in their migration to the hemocoel.     

The characteristics of light in floral induction in vitro of Cichorium intybus. The possible role of phytochrome

The action of light in the initiation of floral buds in vitro has been studied using monochromatic light qualities on root explants of a long day plant, Cichorium intybus L. cv. Witloof. Red light (660 nm, 0.30 W m^-2) promotes flowering, while far-red (730 nm, 0.31 W m^-2) and irradiation with combined red + far-red (0.20 + 0.41 W m^-2) have no effect. In short day conditions floral response can be obtained in two ways: 1) by interrupting the dark period with 5 brief irradiations of red light (0.45 W m^-2, 12 min) at regular intervals, although these are counteracted by far-red irradiations of equal intensity and duration; 2) by interrupting the long night with 5 h red light applied during the second third of the night, while at the beginning or at the end it is ineffective. Red light efficiency appears to depend on the photosynthetic activity of the tissues, so that flowering increases with increasing intensity of white light and is suppressed if no white light is supplied. The reproductive development is determined by the coordination of proper irradiation conditions with sufficient sensitivity of the perceiving meristematic cells. The period of highest sensitivity to environmental light conditions in the life cycle of a Cichorium root explant occurs between the 8th and the 16th day after the start of the culture. The data strongly suggest that phytochrome is involved in flower induction of Cichorium in vitro.     

Aspects of the numerical and functional respones of the aphid parasite, Aphidius sonchi, in the laboratory

The fecundity, reproductive rates, and adult survival of Aphidius sonchi Marshall (Hymenoptera: Aphidiidae) parasitizing second and third instar nymphs of the sowthistle aphid, Hyperomyzus lactucae (L.) (Homoptera: Aphididae) were measured at six different host densities under constant laboratory conditions. At host densities of less than 50 aphids per flowering shoot per female per day, oviposition constraints resulting from the lack of hosts reduced the number of eggs laid, enhanced the extent of superparasitization and, as a result, effectively lowered the fecundity and reproductive rates of the parasites. Above this host density the parasites laid on average 220–230 eggs, but the effective fecundity and reproductive rates continued to increase with the host density. By contrast, the survivorship of the parasites seemed unaffected by host density, with an average adult life span of 4–5 days at all densities. Analysis of the data showed that the intrinsic rate of increase (r_m) of the parasite varied with the host density and could reach values higher than that of the host under identical conditions. The response of r_m to changes in host density and parasite sex ratio is illustrated.Overall, A. sonchi showed a typical convex functional response, to host density. However, the response showed obvious changes through the parasite's adult life and, furthermore, the rates of changes were not consistent at all host densities. The frequency distributions of parasite eggs were generally indistinguishable from random, and the number of hosts parasitized were predicted satisfactorily by the random oviposition equation.

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Résumé L'étude a porté sure l'influence de 6 densités différentes d'Hyperomyzus lactucae (L.) (Homoptera: Aphididae), en conditions constantes de laboratoire, sur la fécondité, le taux de reproduction et la survie des adultes d'Aphidius sonchi Marshall (Hym. Aphidiidae, parasite des larves de 2e et 3e stades. A des densités inférieures à 50 pucerons par tige fleurie de Sonchus oleraceus L, par femelle et par jour, la limitation de la ponte due à l'absence d'hôtes a réduit le nombre d'oeufs émis, élevé le taux de superparasitisme et, en conséquence, diminué la fécondité et le taux de reproduction des parasites. Aux densités d'hôtes supérieures, les parasites ont pondu, en moyenne, 220 à 230 oeufs, mais la fécondité réelle et les taux de reproduction ont continué à augmenter avec la densité des pucerons. Par contre, la longévité des parasites n'a pas été affectée par la densité des hôtes, avec une durée moyenne de vie de 4 à 6 jours. L'analyse des données a montré que le taux d'accroissement intrinsèque (r_m) du parasite a changé avec la densité des hôtes, et pourrait atteindre des valeurs supérieures à celles de l'ôte sous des conditions identiques. Les réponses de r_m aux changements de densité des hôtes et au taux sexuel du parasite sont expliquées.Globalement, A. sonchi a présenté une réponse fonctionnelle convexe typique à la densité des hôtes. Cependant, cette réponse a changé au cours de la vie des images et, de plus, les taux de changement ne sont pas logiques à toutes les densités d'hôtes La fréquence de distribution des oeufs n'est généralement pas séparable d'une distribution au hasard, et le nombre d'hôtes parasites peut être prédit d'une façon satisfaisante en utilisant une équation de ponte au hasard.

     

Relative efficiency of two mating systems and selection procedures for yield improvement in wheat (Triticum aestivum L.)

Summary The relative efficiences of the biparental mating systems and selfing series in connection with phenotypic and geno-phenotypic selection procedures were evaluated for yield improvement in a cross HP1102 X CPAN 1681 of wheat. Two selection cycles having a 4 per cent selection intensity for grain yield were carried out following both selection procedures under the two mating systems. Following these selection procedures, a greater improvement for grain yield could be achieved with the biparental mating system than with the selfing series. During the first selection cycle, the geno-phenotypic selection procedure had an edge over phenotypic selection procedure. The realized response due to the second cycle of selection and the predicted response for the third selection cycle indicated that the phenotypic selection procedure is more efficient than the geno-phenotypic selection procedure. It is suggested that selection following intermating in early segregating generations is able to overcome several inherent limitations of the simple pedigree method as it is possible to increase genetic variation and to concentrate favourable genes and gene combinations for grain yield. An increase in grain yield was, in general, accompanied by an increase in plant height, peduncle length, 100 grain weight, tiller number and biological yield. Therefore, it is suggested that an index comprised of grain yield, plant height, tiller number, grain weight and biological yield could be used for selecting high yielding genotypes of suitable height.     

Response and fertility of dairy heifers following injection with prostaglandin F(2alpha) during early, middle or late diestrus

After an observed estrus, 250 dairy heifers were injected once with 25 mg of PGF(2alpha) either on cycle days 5 through 7 (E), 8 through 11 (M) or 12 through 15 (L). For five days after the PGF(2alpha) injection, heifers were inseminated at about 12 h after estrus was first observed. Observed estrual response rates were 43.0%, 83.6% and 100% for E, M and L, respectively. Average time from PGF(2alpha) to observation of estrus for E, M and L was 59, 70 and 72 h. Conception rates for heifers responding to PGF(2alpha) were 56.8%, 62.1% and 78.3% for E, M and L, respectively. Based on blood samples drawn at the time of PGF(2alpha) injection, progesterone concentration was significantly correlated with response rate but not with conception rate. When compared with M and L, E had a significantly lower response rate and conception rate as well as a shorter period between injection of PGF(2alpha) and observation of estrus.     

Dose dependent responses of cattle to Theileria parva stabilate

Dolan T. T., Young A.S., Losos G.J., McMillan I., Minder Ch.E. and Soulsby K. 1984. Dose dependent responses of Theileria parva stabilate. International Journal for Parasitology14: 89–95. A tick derived stabilate of Theileria parva (Maguga) was titrated in a large group of Boran (Bos indicus) cattle of the same age, sex and origin. The infectivity data was analysed using the independent action model. The cattle were identified as heterogeneous in their response to infection with 75% showing one ID₅₀ (0.0014) and 25% showing another (0.01). The disease responses of the cattle given different dose levels were compared for a variety of parameters. The results obtained showed these parameters to be dose dependent including the time to onset of piroplasm parasitaemia. The stabilate is of large volume and can be used for controlled challenge in immunity studies and for comparison of susceptibility between cattle of different breeds and from different epidemiological backgrounds.     

Histopathological and ultrastructural changes in the antennal gland,midgut, hepatopancreas,and gill of grass shrimp following exposure to hexavalent chromium

Grass shrimp, Palaemonetes pugio, were exposed for 1 month to subacute concentrations of hexavalent chromium (0.5, 1.0, 2.0, 4.0 ppm) after which the gills, midgut, hepatopancreas, and antennal glands were examined for histopathological and ultrastructural changes. Pathological changes were greatest in the antennal glands, followed by hepatopancreas, gills, and midgut. Severe changes occurred in some shrimp, even at 0.5 ppm chromium. Cells of all tissues frequently had both swollen mitochondria and rough endoplasmic reticulum. Small, spherical or ring-like intranuclear inclusions, possibly indicative of cellular hyperactivity or manifestions of chromium and/or protein complexes, were most prevalent in the hepatopancreas and antennal glands but also occurred in the midgut and gills. Other major degenerative changes in the antennal glands were restricted to the labyrinth and included diminution of basal plasmalemmal infoldings and cytoplasmic density, nuclear hypertrophy followed by widespread nuclear pyknosis and epithelial desquamation. In severely altered hepatopancreas hypertrophy was indicated for the basal laminae, nuclei, and possibly for the nucleoli. There was an apparent reduction in mitotic events and many observed mitotic nuclei were abnormal. Abnormal midgut hypertrophy was present in only 8 of 20 examined shrimp, exposed to 0.5 and 1 ppm chromium. Further, the gills of only 10 of the 40 examined chromium-exposed shrimp possessed abnormal features detectable with ligh microscopy. Ultrastructural analysis of the latter indicated an increase in lysosomes and a decrease in cytoplasmic density. In addition, there was a pronounced diminution in the degree of lamellar, subcuticular plasmalemmal infolding. This latter feature is postulated to be a mechanism for the regulation of chromium influx. Possible explanations for most observed alterations in the above tissues are proposed.