Absence Of DDT Research Articles

DDT resistance, epistasis and male fitness in flies

In Drosophila melanogaster, the DDT resistance allele (DDT-R) is beneficial in the presence of DDT. Interestingly, DDT-R also elevates female fitness in the absence of DDT and existed in populations before DDT use. However, DDT-R did not spread regardless of DDT-independent selective advantages in females. We ask whether sexual antagonism could explain why DDT-R did not spread before pesticide use. We tested pre- and post-copulatory male fitness correlates in two genetic backgrounds into which we backcrossed the DDT-R allele. We found costs to DDT-R that depended on the genetic background in which DDT-R was found and documented strong epistasis between genetic background and DDT-R that influenced male size. Although it remains unclear whether DDT-R is generally sexually antagonistic, or whether the fitness costs noted would be sufficient to retard the spread of DDT-R in the absence of DDT, general fitness advantages to DDT-R in the absence of DDT may be unlikely.

MATING PREFERENCE AND ITS RELEVANCE TO ADAPTATION IN DROSOPHILA MELANOGASTER: INVERSION POLYMORPHISM AND DDT RESISTANCE.

The importance of adult mating success as a component of fitness influencing inversion polymorphism in two DDT-resistant populations of Drosophila melanogaster was investigated. The polymorphism involved In(3R)P and the Standard (St) gene arrangement. In population 731R the St/St females showed greater mating propensity than In/In females, while in population J2 the In/In females showed a significant positive association between mating propensity and the percentage of St/St males present. Mating preference data showed that St/St males were selectively favored over In/In males in both populations. No differences were observed between St/St and St/In karyotypes in either population. Frequency-dependent mating in the form of a rare male mating disadvantage for the In/In males tested against the St/St males in 731R was observed; the St/St males in this case showed a marginally significant rare male mating advantage. Thus, mating success as well as previously measured fecundity and fertility all indicate a selective advantage of the St chromosome over the In chromosome in both populations. This fitness relationship does not predict the equilibrium condition of 70-80% St/In, 20-30% In/In, and 0-10% St/St found in the DDT environment, whereas previously collected larval viability data and estimated adult survivorship do. In at least one population (731R), the adult mating success data do predict the dynamics of the polymorphism in the absence of DDT, whereas viability does not. These results, although limited to two populations under two environments (presence or absence of DDT), suggest that the relationship between adaptation to the environment under study and various components of fitness needs to be investigated fully before assessing which fitness components are most important in determining the effects of natural selection in specific populations.

Interactions of Radioprotectors and Oxygen in Cultured Mammalian Cells: I. Dithiothreitol Effects on Radiation-Induced Cell Killing

Radioprotection in vitro by sulfhydryl (SH)-containing compounds is usually greater in aerated than in hypoxic cells. This observation has been cited recently as one of the reasons for the relatively greater effectiveness of radioprotectors such as WR-2721 in normal tissues compared to tumor cells. It is demonstrated herein, however, that hypoxic V79 cells irradiated in vitro under carefully controlled conditions are protected to a greater extent by low concentrations (1-2 mM) of the SH compound dithiothreitol (DTT) than are aerated cells. The reverse, more general phenomenon is seen at high concentrations of DTT (greater than 2 mM). This complex SH concentration and oxygenation dependence results in an increase in the oxygen enhancement ratio (OER) at low concentrations of DTT relative to the OER in the absence of DDT, followed by a decrease in OER at concentrations greater than 2 mM DTT. The possible radiation chemical basis for this finding and its importance to the clinical use of SH-containing radioprotectors are discussed.

Forest malaria in Bangladesh. II. Transmission by Anopheles dirus.

Seasonal, holoendemic malaria transmission in a small, isolated forest community was studied by doing outdoor and indoor all-night man-biting catches over 21 consecutive months. More than 3.8% of Anopheles dirus (=An. balabacensis s.l.), the most frequently caught anopheline, were infective. One An. annularis was also infective. Transmission occurred only during the 7-month monsoon. In the absence of DDT, An. dirus bit with equal frequency indoors and outdoors. When DDT was present in dwellings, fewer females fed indoors and they fed earlier. Feeding pattern was influenced by the phase of the moon: peak outdoors feeding was sharpest and earliest at first quarter and came later as the moon rose later. An average 31% of biting An. dirus lived long enough to reach infectivity of P. falciparum. Although fewer than 10 females fed per man per night, a resident could have received more than 100 infective bites in 2 years. Correlation between actual and calculated rates of gametocytemia were poorest in months when calculated survival rates of mosquitoes were most suspect.

DDT Effect on Rats Raised on Alpha-protein Rations: Growth and storage of liver vitamin A

Rats have been raised on rations containing alpha-protein as the sole source of nitrogen, and growth and liver vitamin A levels have been observed as a function of the rate of methionine supplement in the presence and absence of DDT. Increasing the level of methionine supplement in increments from zero to 4 g/kg produced a progressive increase in the growth of male rats. Females showed maximum growth when the methionine level was 1.0 g/kg. In the absence of added methionine DDT depressed growth, but at levels greater than 1.0 g/kg DDT stimulated growth. The level of vitamin A stored in the liver was depressed by feeding DDT, with the response being dependent on the level of methionine in the diet. The most pronounced reduction was observed with the unsupplemented ration, and the DDT effect was virtually eliminated when methionine was added at a level of 4 g/kg. A mechanism has been proposed for this interaction based on the action of DDT and methionine on the processes responsible for the absorption and transport of vitamin A.

Comparison of different organic and copper fungicides and some combinations of fungicides with ddt for the control of potato diseases and insects

There is a need for a material that can effectively replace Bordeaux mixture as a spray material for potatoes. Bordeaux mixture depressed the yield rate despite the fact that it gave good control of flea beetles and the blight diseases. Phygon, Karbam Z, and Dithane appear to be promising organic fungicides for potatoes but lack the ability to control flea beetle injury. DDT, when used with different fungicides, increased the yield rate from 55 to 115 bushels per acre or from 16.3 to 32.1 per cent. Certain shortcomings of the neutral copper and organic fungicides are greatly offset when applied with DDT. A neutral copper or organic fungicide may replace Bordeaux if used in combination with DDT or similar insecticides. The protective value of some spray fungicides for the control of early and late blight has increased when used in combination with DDT. Also the protective value of DDT for the control of flea beetles likewise was increased by being combined with a fungicide. DDT reduced the aphid population about 80 per cent which was sufficient to prevent the excessive injury and thus the yield was increased. The different fungicides in the absence of DDT differed regarding the relative aphid population that developed on the sprayed plants.