Mutation of AtPME2, a pH-Dependent Pectin Methylesterase, Affects Cell Wall Structure and Hypocotyl Elongation

Pectin methylesterases (PMEs) modify homogalacturonan's chemistry and play a key role in regulating primary cell wall mechanical properties. Here, we report on Arabidopsis AtPME2, which we found to be highly expressed during lateral root emergence and dark-grown hypocotyl elongation. We showed that dark-grown hypocotyl elongation was reduced in knock-out mutant lines as compared to the control. The latter was related to the decreased total PME activity as well as increased stiffness of the cell wall in the apical part of the hypocotyl. To relate phenotypic analyses to the biochemical specificity of the enzyme, we produced the mature active enzyme using heterologous expression in Pichia pastoris and characterized it through the use of a generic plant PME antiserum. AtPME2 is more active at neutral compared to acidic pH, on pectins with a degree of 55-70% methylesterification. We further showed that the mode of action of AtPME2 can vary according to pH, from high processivity (at pH8) to low processivity (at pH5), and relate these observations to the differences in electrostatic potential of the protein. Our study brings insights into how the pH-dependent regulation by PME activity could affect the pectin structure and associated cell wall mechanical properties.

The maize low-lignin brown midrib3 mutant shows pleiotropic effects on photosynthetic and cell wall metabolisms in response to chilling

Maize (Zea mays L.) is one of the major cereal crops in the world and is highly sensitive to low temperature. Here, changes in photosynthetic and cell wall metabolisms were investigated during a long chilling exposure in inbred line F2 and a low-lignin near-isogenic brown midrib3 mutant (F2bm3), which has a mutation in the caffeic acid O-methyltransferase (COMT) gene. Results revealed that the plant biomass was reduced, and this was more pronounced in F2bm3. Photosynthesis was altered in both lines with distinct changes in photosynthetic pigment content between F2bm3 and F2, indicating an alternative photoprotection mechanism between lines under chilling. Starch remobilization was observed in F2bm3 while concentrations of sucrose, fructose and starch increased in F2, suggesting a reduced sugar partitioning in F2. The cell wall was altered upon chilling, resulting in changes in the composition of glucuronorabinoxylan and a reduced cellulose level in F2. Chilling shifted lignin subunit composition in F2bm3 mutant to a higher proportion of p-hydroxyphenyl (H) units, whereas it resulted in lignin with a higher proportion of syringyl (S) residues in F2. On average, the total cell wall ferulic acid (FA) content increased in both genotypes, with an increase in ether-linked FA in F2bm3, suggesting a greater degree of cross-linking to lignin. The reinforcement of the cell wall with lignin enriched in H-units and a higher concentration in cell-wall-bound FA observed in F2bm3 as a response to chilling, could be a strategy to protect the photosystems.

The COVID-19 pandemic in francophone West Africa: from the first cases to responses in seven countries

Background

In early March 2020, the COVID-19 pandemic hit West Africa. In response, countries in the region quickly set up crisis management committees and implemented drastic measures to stem the spread of the SARS-CoV-2 virus. The objective of this article is to analyse the epidemiological evolution of COVID-19 in seven Francophone West African countries (Benin, Burkina Faso, Côte d’Ivoire, Guinea, Mali, Niger, Senegal) as well as the public health measures decided upon during the first 7 months of the pandemic.

Methods

Our method is based on quantitative and qualitative data from the pooling of information from a COVID-19 data platform and collected by a network of interdisciplinary collaborators present in the seven countries. Descriptive and spatial analyses of quantitative epidemiological data, as well as content analyses of qualitative data on public measures and management committees were performed.

Results

Attack rates (October 2020) for COVID-19 have ranged from 20 per 100,000 inhabitants (Benin) to more than 94 per 100,000 inhabitants (Senegal). All these countries reacted quickly to the crisis, in some cases before the first reported infection, and implemented public measures in a relatively homogeneous manner. None of the countries implemented country-wide lockdowns, but some implemented partial or local containment measures. At the end of June 2020, countries began to lift certain restrictive measures, sometimes under pressure from the general population or from certain economic sectors.

Conclusion

Much research on COVID-19 remains to be conducted in West Africa to better understand the dynamics of the pandemic, and to further examine the state responses to ensure their appropriateness and adaptation to the national contexts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-11529-7.

The exogenous application of AtPGLR, an endo-polygalacturonase, triggers pollen tube burst and repair

Plant cell wall remodeling plays a key role in the control of cell elongation and differentiation. In particular, fine-tuning of the degree of methylesterification of pectins was previously reported to control developmental processes as diverse as pollen germination, pollen tube elongation, emergence of primordia or elongation of dark-grown hypocotyls. However, how pectin degradation can modulate plant development has remained elusive. Here we report the characterization of a polygalacturonase (PG), AtPGLR, the gene for which is highly expressed at the onset of lateral root emergence in Arabidopsis. Due to gene compensation mechanisms, mutant approaches failed to determine the involvement of AtPGLR in plant growth. To overcome this issue, AtPGLR has been expressed heterologously in the yeast Pichia pastoris and biochemically characterized. We showed that AtPGLR is an endo-PG that preferentially releases non-methylesterified oligogalacturonides with a short degree of polymerization (< 8) at acidic pH. The application of the purified recombinant protein on Amaryllis pollen tubes, an excellent model for studying cell wall remodeling at acidic pH, induced abnormal pollen tubes or cytoplasmic leakage in the subapical dome of the pollen tube tip, where non-methylesterified pectin epitopes are detected. Those leaks could either be repaired by new β-glucan deposits (mostly callose) in the cell wall or promoted dramatic burst of the pollen tube. Our work presents the full biochemical characterization of an Arabidopsis PG and highlights the importance of pectin integrity in pollen tube elongation.

[Efficacy against Malaria Vectors of Long-Lasting Insecticide-Treated Mosquito Nets after 17 Months of Use in the City of Bouaké, in the Center of Côte d'Ivoire]

Malaria remains a public health problem in Côte d'Ivoire despite a 95% coverage rate with long-lasting insecticide-treated mosquito nets (LLINs) since 2015. A study was conducted in Bouaké to determine the residual efficacy of LLINs used during 17 months (N = 30) and of stored and unpacked LLINs (N = 8). The physical integrity of LLINs and their biological efficacy on populations of Anopheles gambiae (sensitive and resistant to insecticides) were assessed. The study revealed that 57% (17/30) of LLINs recovered from households have a hole. The proportional hole indices indicated that 70% (21/30) of LLINs were in good condition, 20% (6/30) were repairable and 10% (3/30) were unusable.This study also showed that the LLINs used and stored were effective on the sensitive Kisumu strain but ineffective on resistant populations of An. gambiae of Bouaké. Average knock-down and mortality rates induced by LLINs used on the populations of An. gambiae from Bouaké were 23% and 9%, respectively. The resistance of mosquitoes to insecticides and the alteration of the physil integrity of mosquito nets are probably major factors to be taken into account in estimating the efficacy of LLINs in the field.

Cytological Approaches Combined With Chemical Analysis Reveals the Layered Nature of Flax Mucilage

The external seed coat cell layer of certain species is specialized in the production and extrusion of a polysaccharide matrix called mucilage. Variations in the content of the released mucilage have been mainly associated with genetically regulated physiological modifications. Understanding the mucilage extrusion process in crop species is of importance to gain deeper insight into the complex cell wall biosynthesis and dynamics. In this study, we took advantage of the varying polysaccharide composition and the size of the flax mucilage secretory cells (MSCs) to study mucilage composition and extrusion in this species of agricultural interest. We demonstrate herein that flax MSCs are structured in four superimposed layers and that rhamnogalacturonans I (RG I) are firstly synthesized, in the upper face, preceding arabinoxylan and glucan synthesis in MSC lower layers. Our results also reveal that the flax mucilage release originates from inside MSC, between the upper and deeper layers, the latter collaborating to trigger polysaccharide expansion, radial cell wall breaking and mucilage extrusion in a peeling fashion. Here, we provide evidence that the layer organization and polysaccharide composition of the MSCs regulate the mucilage release efficiency like a peeling mechanism. Finally, we propose that flax MSCs may represent an excellent model for further investigations of mucilage biosynthesis and its release.

PME58 plays a role in pectin distribution during seed coat mucilage extrusion through homogalacturonan modification

Pectins are major components of plant primary cell walls. They include homogalacturonans (HGs), which are the most abundant pectin and can be the target of apoplastic enzymes like pectin methylesterases (PMEs) that control their methylesterification level. Several PMEs are expressed in the seed coat of Arabidopsis thaliana, particularly in mucilage secretory cells (MSCs). On the basis of public transcriptomic data, seven PME genes were selected and checked for their seed-specific expression by quantitative reverse transcription PCR. Of these, PME58 presented the highest level of expression and was specifically expressed in MSCs at the early stages of seed development. pme58 mutants presented two discrete phenotypes: (i) their adherent mucilage was less stained by ruthenium red when compared to wild-type seeds, but only in the presence of EDTA, a Ca(2+)chelator; and (ii) the MSC surface area was decreased. These phenotypes are the consequence of an increase in the degree of HG methylesterification connected to a decrease in PME activity. Analysis of the sugar composition of soluble and adherent mucilage showed that, in the presence of EDTA, sugars of adherent mucilage were more readily extracted in pme58 mutants. Immunolabelling with LM19, an antibody that preferentially recognizes unesterified HGs, also showed that molecular interactions with HGs were modified in the adherent mucilage of pme58 mutants, suggesting a role of PME58 in mucilage structure and organization. In conclusion, PME58 is the first PME identified to play a direct role in seed mucilage structure.

PECTIN METHYLESTERASE48 is involved in Arabidopsis pollen grain germination

Germination of pollen grains is a crucial step in plant reproduction. However, the molecular mechanisms involved remain unclear. We investigated the role of PECTIN METHYLESTERASE48 (PME48), an enzyme implicated in the remodeling of pectins in Arabidopsis (Arabidopsis thaliana) pollen. A combination of functional genomics, gene expression, in vivo and in vitro pollen germination, immunolabeling, and biochemical analyses was used on wild-type and Atpme48 mutant plants. We showed that AtPME48 is specifically expressed in the male gametophyte and is the second most expressed PME in dry and imbibed pollen grains. Pollen grains from homozygous mutant lines displayed a significant delay in imbibition and germination in vitro and in vivo. Moreover, numerous pollen grains showed two tips emerging instead of one in the wild type. Immunolabeling and Fourier transform infrared analyses showed that the degree of methylesterification of the homogalacturonan was higher in pme48-/- pollen grains. In contrast, the PME activity was lower in pme48-/-, partly due to a reduction of PME48 activity revealed by zymogram. Interestingly, the wild-type phenotype was restored in pme48-/- with the optimum germination medium supplemented with 2.5 mm calcium chloride, suggesting that in the wild-type pollen, the weakly methylesterified homogalacturonan is a source of Ca(2+) necessary for pollen germination. Although pollen-specific PMEs are traditionally associated with pollen tube elongation, this study provides strong evidence that PME48 impacts the mechanical properties of the intine wall during maturation of the pollen grain, which, in turn, influences pollen grain germination.

Structural alteration of cell wall pectins accompanies pea development in response to cold

Pea (Pisum sativum) cell wall metabolism in response to chilling was investigated in a frost-sensitive genotype 'Terese' and a frost-tolerant genotype 'Champagne'. Cell walls isolated from stipules of cold acclimated and non-acclimated plants showed that cold temperatures induce changes in polymers containing xylose, arabinose, galactose and galacturonic acid residues. In the tolerant cultivar Champagne, acclimation is accompanied by increases in homogalacturonan, xylogalacturonan and highly branched Rhamnogalacturonan I with branched and unbranched (1→5)-α-arabinans and (1→4)-β-galactans. In contrast, the sensitive cultivar Terese accumulates substantial amounts of (1→4)-β-xylans and glucuronoxylan, but not the pectins. Greater JIM7 labeling was observed in Champagne compared to Terese, indicating that cold acclimation also induces an increase in the degree of methylesterification of pectins. Significant decrease in polygalacturonase activities in both genotypes were observed at the end of cold acclimation. These data indicate a role for esterified pectins in cold tolerance. The possible functions for pectins and their associated arabinans and galactans in cold acclimation are discussed.

[Family environment and dental health disparities among urban children in Burkina Faso]

BACKGROUND

Dental caries is the most common multifactorial disease in children and has substantial negative impact on daily life. In sub-Saharan Africa, few data are available on the relationship between dental caries and the social and family environment of children. The objectives of the present study were firstly to assess the level of prevalence and severity of dental caries of children in Ouagadougou, the capital city of Burkina Faso and secondly to determine whether or not individual factors, family and living conditions are linked with dental health disparities within the population.

METHODS

Interview and clinical data were obtained from a household-based cross-sectional survey. A two-stage stratified sampling technique was applied in four areas of Ouagadougou representing different stages of urbanization.

RESULTS

The final study population included 1606 children aged 6-12 years. For the overall group the total caries prevalence rate was 48.2%. Results showed that the dental health status of the mother, social integration of the householder and socioeconomic level of the household were associated with the dental health of children. Disparities in dental health were prominent; poor dental health was relatively frequent in children from households poorly integrated into social networks with rather acceptable standard in terms of material wealth.

CONCLUSION

Our study showed that individual factors as well as family-related and environmental factors had an influence on their caries experience. The rapidly changing lifestyle affects oral health and the burden of oral diseases is expected to increase initially in people of upper classes and later in disadvantaged people. Disease prevention focussing on common risk factors of chronic diseases should be enhanced. In addition, the accessibility of quality fluoride products (e.g. toothpaste, salt, water) should be facilitated as soon as possible.

Identification of pectin methylesterase 3 as a basic pectin methylesterase isoform involved in adventitious rooting in Arabidopsis thaliana

• Here, we focused on the biochemical characterization of the Arabidopsis thaliana pectin methylesterase 3 gene (AtPME3; At3g14310) and its role in plant development. • A combination of biochemical, gene expression, Fourier transform-infrared (FT-IR) microspectroscopy and reverse genetics approaches were used. • We showed that AtPME3 is ubiquitously expressed in A. thaliana, particularly in vascular tissues. In cell wall-enriched fractions, only the mature part of the protein was identified, suggesting that it is processed before targeting the cell wall. In all the organs tested, PME activity was reduced in the atpme3-1 mutant compared with the wild type. This was related to the disappearance of an activity band corresponding to a pI of 9.6 revealed by a zymogram. Analysis of the cell wall composition showed that the degree of methylesterification (DM) of galacturonic acids was affected in the atpme3-1 mutant. A change in the number of adventitious roots was found in the mutant, which correlated with the expression of the gene in adventitious root primordia. • Our results enable the characterization of AtPME3 as a major basic PME isoform in A. thaliana and highlight its role in adventitious rooting.

The transcription factor BELLRINGER modulates phyllotaxis by regulating the expression of a pectin methylesterase in Arabidopsis

Plant leaves and flowers are positioned along the stem in a regular pattern. This pattern, which is referred to as phyllotaxis, is generated through the precise emergence of lateral organs and is controlled by gradients of the plant hormone auxin. This pattern is actively maintained during stem growth through controlled cell proliferation and elongation. The formation of new organs is known to depend on changes in cell wall chemistry, in particular the demethylesterification of homogalacturonans, one of the main pectic components. Here we report a dual function for the homeodomain transcription factor BELLRINGER (BLR) in the establishment and maintenance of the phyllotactic pattern in Arabidopsis. BLR is required for the establishment of normal phyllotaxis through the exclusion of pectin methylesterase PME5 expression from the meristem dome and for the maintenance of phyllotaxis through the activation of PME5 in the elongating stem. These results provide new insights into the role of pectin demethylesterification in organ initiation and cell elongation and identify an important component of the regulation mechanism involved.

Major changes in the cell wall during silique development in Arabidopsis thaliana

Fruit development is a highly complex process, which involves major changes in plant metabolism leading to cell growth and differentiation. Changes in cell wall composition and structure play a major role in modulating cell growth. We investigated the changes in cell wall composition and the activities of associated enzymes during the dry fruit development of the model plant Arabidopsis thaliana. Silique development is characterized by several specific phases leading to fruit dehiscence and seed dispersal. We showed that early phases of silique growth were characterized by specific changes in non-cellulosic sugar content (rhamnose, arabinose, xylose, galactose and galacturonic acid). Xyloglucan oligosaccharide mass profiling further showed a strong increase in O-acetylated xyloglucans over the course of silique development, which could suggest a decreased capacity of xyloglucans to be associated with each other or to cellulose. The degree of methylesterification, mediated by the activity of pectin methylesterases (PMEs), decreased over the course of silique growth and dehiscence. The major changes in cell wall composition revealed by our analysis suggest that it could be major determinants in modulating cell wall rheology leading to growth or growth arrest.

[Land-use and urinary schistosomiasis in Daloa (Côte d'Ivoire)]

The relation between agricultural land development of inland-valleys and health population has been studied in a town of the Ivorian forest area using urinary schistosomiasis as an indicator. Snails were collected during 4 months in rice fields and water holes used for market gardening of two urban inland-valleys (Batagnihi and Gakognihi). Prevalence of schistosomiasis was evaluated in two districts, Kennedy II and Fadiga, located close to the investigated inland-valleys. Schistosomiasis risk was higher in the Batagnihi where rice cultivation was more developed and prevalence of urinary schistosomiasis was higher in the Kennedy II district which is close to this inland-valley particularly among the Northern migrant people. The Kennedy II population has much more contacts with the inland-valley because of rice cultivation and social status. The higher socio-economic level of the Fadiga population limiting its contacts with the inland-valley can explain this result.

[African towns and health: references and stakes]

Urbanization is a fairly recent phenomenon. Thus during the 19th century, only 5% of the population was living in town. However it is more and more important as urban population has been multiplied by 15 since 1900. In Africa, this evolution is still more recent and the continent remains poorly urbanized. But the rate of urbanization is the fastest in the world and demographic forecasts indicate that by 2025, more than 50% of the African population will live in towns. Consequences of urbanization on human development are not well known. Concepts of demographic and epidemiological transitions were widely used for health. Health transition is another concept, including cultural, social and behavioural determining factors as well as ways of caring and being cared for. These processes account for the reduction of infectious diseases through a fall of mortality and birth rates and the emergence of non-transmissible diseases like cardiovascular diseases, cancers, mental diseases.... Although health situation is depicted as better in towns (better immunization, health care offer, better access to health care...), mortality and morbidity patterns seem to change more quickly in towns than in rural areas. However this is not true everywhere in urban areas where several towns are to be found within the same town and for example, health of populations living on margins may be worse than that of rural populations. Urban people resort to modern health care together with traditional healers, even informal, sometimes illegal health care, involving heavy costs but offering no guarantee as regards their quality and their efficiency for patients and society. It appears that developing countries have to face a new health care demand quite different from the one they used to face before, when they have simultaneously to cope with uncontrolled town growth. Under these conditions, urban health should become a priority.

[Role of patient travel in transmission of human African trypanosomiasis in a highly endemic area of the Ivory Coast]

Human African trypanosomosis (HAT) remains a major public health problem in Subsaharan Africa. The region around the town of Bonon in middle western Côte d'Ivoire is a highly endemic HAT zone. The purpose of this study was to assess the role of travelling of infected patients in transmission of HAT. The study population included a total of 96 patients in whom HAT had been diagnosed actively or passively between 1999 and 2000. Information on each patient's residence and workplaces, i.e. water site, and farm field, was used to calculate the mean distance traveled and mean number of places visited daily by each patient. Findings indicated that both parameters, i.e., distance traveled and number of places visited, were significantly higher for patients living in Bonon than those living in hamlets or homesteads. Based on analysis of patient movements the endemic zone could be divided into three subdivisions with different modes of disease transmission. This study was performed as a preliminary step for a larger investigation designed to allow specific targeting of HAT hot spots based mainly on a geographic information system.

Host age and time of exposure in Trypanosoma brucei gambiense Human African Trypanosomiasis

Human African Trypanosomiasis is related to behavioural risk factors but complex interactions exist between (i) environmental and behavioural risk factors, (ii) vector and (iii) human host. Our aim was to investigate the interrelationships between previously analysed risk factors and the roles of age and time of exposure according to ethnic group and migration status. However, this descriptive and retrospective study is based on cases only (no controls) and our results must therefore be regarded as hypothesis-generating. Individuals originating from areas where sleeping sickness is absent and who settle in an endemic area seem to develop the disease after a shorter time of exposure than native subjects from endemic areas. Our results emphasise the complexity of vector-transmitted disease epidemiology, involving behavioural and/or environmental risk factors on the one hand, and more individual ones such as ageing, immunity and genetic background on the other hand.

[Integration of demographic factors in the characterization of risk areas for sleeping sickness in Côte d'Ivoire]

The purpose of this study was to classify the risk for transmission of African human trypanosomiasis (sleeping sickness) according to population and settlement densities in four different areas of Zoukougbeu, Cote d'Ivoire, where the exact location of cases reported since 1990 is known. Epidemiological risk indexes were calculated from entomological data obtained from three surveys and analyzed with respect to presence of patients and occupancy rate in each area. Results indicated that there was a risk of transmission near the village of Bahigbeu II where the population density is between 30 and 40 inhabitants per km2 and settlement density is 4 per km2. There was also a risk in less inhabited areas such as Ouatigbeu where the population density is less than 30 inhabitants per km2 and dwelling density less than 4 per km2. In fact, cases are regularly reported in Ouatigbeu but never in Bahigbeu II. Based on these findings, we conclude that, while land occupancy can be considered as a risk factor for sleeping sickness, other factors such as human mobility must be taken into account to characterize risk areas and predict outbreaks.

Impact of the development of agricultural land on the transmission of sleeping sickness in Daloa, Côte d'Ivoire

Although tools to control sleeping sickness do exist, their use is difficult; areas where intervention is most required often cannot be targeted for lack of appropriate risk indicators. The importance of human behaviour and habits in the manifestation of the disease is clear. In the development of effective new approaches to the control of the disease, information must be gathered about human populations, and their interaction with the environment, in rural as well as in urban and peri-urban areas. The results of a study carried out in Daloa show that use of some methods for the development of agricultural land leads to increased human-vector contact and, as a result, increased risk of sleeping sickness. Such land-management methods may therefore be useful as risk indicators for transmission. Transmission does not occur in the town of Daloa itself but in surrounding areas under cultivation. The use of the epidemiological risk index seems to be inappropriate in urban (and perhaps peri-urban) areas. The results emphasise not only the importance of environmental and demographic data in elucidating the epidemiology of human trypanosomiasis but also the need for further investigations in peri-urban areas.

[Age group distribution of Glossina palpalis palpalis females in plantations and shallow water of the forest region of Côte d'Ivoire. Relation to the prevalence of sleeping sickness]

In epidemiologically dangerous biotopes of foci with high prevalence of Human African Trypanosomiasis (HAT), different female age groups (nulliparous, young parous, old parous) were observed in the same proportions. On the contrary, in areas without HAT or in low prevalence foci (< 0.2%), these proportions significantly differed. Female age group distribution in epidemiologically dangerous biotopes could thus be a good indication by which to guide the control of Human African Trypanosomiasis (HAT).

Effects of urbanization on transmission of human African trypanosomiasis in a suburban relict forest area of Daloa, Côte d'Ivoire

The epidemiological risk of human African trypanosomiasis transmission was evaluated from entomological parameters (apparent trap density, female teneral rates, daily survival rates, proportion of human feeds) of tsetse (Glossina palpalis palpalis) populations in the town of Daloa, Côte d'Ivoire. High tsetse densities were found in the town outskirts, where the calculated risk of transmission was greatest. Environmental changes brought about by urbanization did not result in the disappearance of tsetse, or the interruption of sleeping sickness transmission. The few cases of sleeping sickness detected (32) in the years 1990-95 indicated that transmission was unrelated to tsetse density.

[Geographic approach to urinary schistosomiasis in an average African town, Daloa (Ivory Coast)]

Agricultural activity occurs within many medium size towns in developing countries. Rural influences and urbanization, which may be well or poorly managed, combine to create new health problems. A geographical approach is useful for evaluating the ability of the health care system to deal efficiently with these problems. Such an approach should take into account the urban environment and human population, health care and spatial differentiation factors. Relevant health indicators were selected to analyze the geographical patterns of health risk and of the health care system. These factors were analyzed according to area, at various levels. Field studies were carried out and aerial photographs and the various available maps were also studied. Results were compared to determine whether the health care system was appropriate for the health needs of the town. Urinary schistosomiasis is a useful example for assessing the value of the suggested methodology. The risk of transmission of this disease is high so its early detection is vital. The ability of the health care system to detect infection was assessed.

Effects of two insect growth regulators on the susceptibility of Aedes aegypti (Diptera:Culicidae) to Molinema dessetae (Nematoda:Filarioidea)

The effects of 2 growth regulators, diflubenzuron (DFB) and OMS 2017, on the ability of females Aedes aegypti to become infected with Molinema dessetae was studied under laboratory conditions. OMS 2017 and DFB had no effect on either the amount of blood ingested or the microfilarial load. The infective potential of females that survived DFB treatment was significantly greater than untreated females, but there was no difference between OMS 2017-treated and control females. The percentage of infective larvae in the head after OMS 2017 and DFB treatments was significantly greater than for control females. Insect growth regulators appear to affect the vectorial competence of mosquitoes, and these results indicate the need for preliminary studies before these compounds are used in large-scale control programs.

A FORTRAN program to simulate the evolution of genetic variability in a small population

This paper presents a FORTRAN-77 program that performs Monte Carlo simulation of the evolution of genetic structure in a small population under selection. The aim is to study the possibility of foreseeing a response plateau in a theoretical population, depending on population size and management, and to apply this to small populations actually selected, to predict a possible exhaustion of genetic variability. A set of subroutines describing the different steps in a selection cycle (birth, expression of phenotypic value, genetic evaluation, selection, reproduction, death) is available and the user can choose the sequence of subroutines, the characteristics of individuals submitted to each step, and also build more personal subroutines if necessary. The program is based on the generation of exact genotypes and their transmission from parents to offspring, through simulation of meiosis and pairing of gametes. Parameters concerning the genome, the initial structure of the population and its management are required. The genetic mean and variance of the population for each new cycle of selection are given as outputs. Examples of applications are given and discussed.

Effects of two insect growth regulators on ecdysteroid production in Aedes aegypti (Diptera: Culicidae)

Diflubenzuron and OMS 2017 are insect growth regulators that affect larval to adult development in Aedes aegypti (L.) by altering ecdysis. When larvae were exposed to sublethal concentrations, surviving adults express reduced reproductive potential. In mosquitoes, ecdysteroids are important in larval and adult ovarian development. We applied 30% emergence reduction concentrations (EI30) of OMS 2017 and diflubenzuron to 4th-instar Ae. aegypti to determine if changes in ecdysteroid production may explain these physiological effects. Ecdysteroid concentrations were measured in the larvae, pupae, and adults after treatment with both IGRs. After treatment with OMS 2017, the 1st peak of ecdysteroid production in larvae was totally inhibited, but after pupation, ecdysteroid concentrations were the same as in untreated controls. In diflubenzuron-treated larvae, the second peak of production was delayed and the ecdysteroid concentrations of the larvae, pupae, and adults were depressed slightly when compared with untreated controls. The production of ecdysteroids by the ovaries was not altered by sublethal larval treatment with both IGRs. Although OMS 2017 and diflubenzuron belong to the same chemical family, their mode of action apparently is different.

Effects of the insect growth regulators OMS 2017 and diflubenzuron on the reproductive potential of Aedes aegypti

The effects of 2 benzoylphenylurea insect growth regulators, OMS 2017 and diflubenzuron, on 4th instar larvae of Aedes aegypti were investigated in the laboratory. Apart from delayed lethal action, possible effects on the reproductive potential were also studied. A baseline concentration of each compound causing 30% emergence inhibition was determined. At this concentration, OMS 2017 affected fecundity of the mosquito but diflubenzuron did not. The fertility of females that survived OMS 2017 exposure also was decreased; 23% of the eggs reached the 4th larval instar. Diflubenzuron did not cause any reduction in fertility. The basal follicle number showed great variability after both treatments as it was alternatively equal, lower, or higher than in the control.