Seasonal occurrence of the yellow stem borer Scirpophaga incertulas (Walker) on deepwater rice in Bangladesh and Thailand

Deepwater rice is grown in South and Southeast Asia on 11 million hectares flooded deeply during the monsoon. Surveys for the incidence of stem borers in deepwater rice in Bangladesh from 1977 to 1980, and in Thailand during 1981 and 1982, showed that borer incidence and species composition were remarkably similar. Scirpophaga incertulas (Walker) usually comprised more than 90% of the borer population and was almost exclusively present during the main flooding period. Chilo polychrysus (Meyr.) comprised 11% and Sesamia inferens (Walker) 6% of the population in the pre-flood and ripening stages.Low borer activity in the early part of the season was explained by a low nucleus population, the synchronous planting of deepwater rice, and severe moisture stress and high temperatures in the pre-flood period. In Bangladesh, a severe drought in 1979 limited Scirpophaga incertulas populations to unusually low levels until the flowering stage. In Thailand, drier conditions, the lack of an intervening rice crop in the dry season and a longer pre-flood period, appeared to severely restrict early season borer activity. The onset of flooding and stem elongation provided a more favourable environment for S. incertulas. Borer activity increased steadily during the first 3–4 months of flooding, to average 23% damaged stems (26 m^?2) and 13 borer immature stages/100 stems (13 m^?2) by the flowering stage. Borer activity continued at about the same level as the water receded, to reach maximum annual levels of 38–44% damaged stems (35 m^?2) at the late-ripening stage. At harvest, 60% of the fields were at outbreak level (>40% damaged stems). Such high levels of damage are explained by the long growth period of deepwater rice, favourable weather during the flooding period, and the optimum habitat of the elongated stem. S. incertulas populations then crashed to low levels; the larvae entering diapause in the field stubble. Although related to actual damage, the deadheart and whitehead symptoms grossly under-estimated the extent of stem damage.     

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Is maternal alpha-fetoprotein screening still of value in a low-risk area for neural tube defects?

Estimation of maternal serum alpha-fetoprotein (AFP) was used as a screening method for the detection of neural tube defects (NTDs) in 6344 women over three years. Of 88 (1.4 per cent) who had one or more serum AFP levels equal to, or greater than, 2.5 multiples of the median (MoM) for the relevant gestational age, 43 (0.68 per cent) underwent amniocentesis. There were eight NTDs. Four of these were screened by serum AFP, and all cases of spina bifida had serum AFP levels greater than 3.0 MoM, including one small open defect which was not seen on ultrasound. The other four cases of NTD, which were not screened, were identified by ultrasound. Of 64 singleton pregnancies 32 (50 per cent) had serum AFP levels between 2.5 and 3.0 MoM, and low birthweight (⪕2500 g) occurred in 29 per cent. Because of improvements in ultrasound techniques and the apparent falling incidence of NTD, the role of serum AFP as the primary screening procedure should be regularly reviewed. Effective screening is dependent on mothers booking early.     

The effect of oxygen tension on colony formation and cell proliferation of amniotic fluid cellsin vitro

The effects of reduced oxygen concentrations in the gas phase over the culture medium on colony formation and cell proliferation were investigated in high and low cell density primary and secondary cultures of amniotic fluid cells. Using two standard culture methods (25 cm² plastic flasks and Leighton type tubes) a significantly reduced culture time was observed at high cell density for mass cultures by incubation within a low oxygen tension gas phase (2.5 per cent to 7.5 per cent O₂) instead of conventional air (18 per cent O₂). At low cell density colony formation was significantly enhanced in cultures grown at reduced oxygen tension. Using gas permeable membranes as support, lowering the oxygen tension from 7.5 per cent to 2.5 per cent yielded an increase in plating efficiency of cells from approximately 5 per cent to 25 per cent, whereas plating efficiency was less than 2 per cent for cells grown at ambient 18 per cent O₂. It is suggested that low oxygen tension in the gas phase is an effective means of enhancing clonal growth in amniotic fluid cell cultures, thereby reducing both culture time and risk of culture failure.     

Prenatal sex diagnosis: Testosterone and fsh levels in mid-trimester amniotic fluids

We studied the validity of mid-trimester amniotic fluid testosterone and FSH in the diagnosis of fetal sex in abnormal fetuses and in twins. It was found that the testosterone/FSH ratio, but not the level of the individual hormones, was an excellent criterion for fetal sex diagnosis. In a control group of 32 female and 34 male fetuses, the testosterone/FSH ratio was diagnostic. In two cases the values were indeterminate and fetal sex could not be predicted, but there were no false diagnoses. The abnormalities of the fetuses were diagnosed by karyotype analyses or raised levels of α-fetoprotein. It was found that neither autosomal trisomies nor X-chromosome aneuploidy or neural tube defect interfered with the diagnostic value of the hormonal approach. The twin study included 14 pairs, three of whom were discordant for sex. In all twins the fetal sex diagnosis was appropriate. In co-twins of the same sex the hormone levels were very close to each other.     

Maternal age specific rates for chromosome aberrations and factors influencing them: Report of a collaborative european study on 52 965 amniocenteses

Maternal age specific rates for all major chromosome aberrations have been determined in 52 965 pregnancies in mothers 35 years of age and over at the time of amniocentesis. Rates increase exponentially with advancing maternal age for trisomies 21, 18 and 13, and for the XXX and XXY syndromes, but in the autosomal trisomies this rise appears to be followed by a levelling off at the upper end of the age range. A significant inverse relationship with maternal age is found for 45,X cases. It is postulated that these various patterns are the result of the interaction of three principal factors: a maternal age effect acting particularly on first meiotic nondisjunction: a higher spontaneous abortion rate with advancing maternal age for aneuploid as compared to euploid conceptions; and an increased probability of spontaneous abortion before the time of amniocentesis for conceptions with more extensive chromosome imbalance. A stepwise logistic regression analysis of 13 299 pregnancies in which both parental ages are known shows that the father's age does not influence these maternal age specific rates, with the possible exception of the 47,XXY syndrome.