Males and females of nearly all animals differ in their body size, a phenomenon called sexual size dimorphism (SSD). The degree and direction of SSD vary considerably among taxa, including among populations within species. A considerable amount of this variation is due to sex differences in body size plasticity. We examine how variation in these sex differences is generated by exploring sex differences in plasticity in growth rate and development time and the physiological regulation of these differences (e.g., sex differences in regulation by the endocrine system). We explore adaptive hypotheses proposed to explain sex differences in plasticity, including those that predict that plasticity will be lowest for traits under strong selection (adaptive canalization) or greatest for traits under strong directional selection (condition dependence), but few studies have tested these hypotheses. Studies that combine proximate and ultimate mechanisms offer great promise for understanding variation in SSD and sex differences in body size plasticity in insects.

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Sex differences in phenotypic plasticity affect variation in sexual size dimorphism in insects: from physiology to evolution.

Knockdown resistance (kdr) is a well-characterized mechanism of resistance to pyrethroid insecticides in many insect species and is caused by point mutations of the pyrethroid target site the para-type sodium channel. The presence of kdr mutations in Anopheles gambiae, the most important malaria vector in Africa, has been monitored using a variety of molecular techniques. However, there are few reports comparing the performance of these different assays. In this study, two new high-throughput assays were developed and compared with four established techniques. Fluorescence-based assays based on 1) TaqMan probes and 2) high resolution melt (HRM) analysis were developed to detect kdr alleles in An. gambiae. Four previously reported techniques for kdr detection, Allele Specific Polymerase Chain Reaction (AS-PCR), Heated Oligonucleotide Ligation Assay (HOLA), Sequence Specific Oligonucleotide Probe – Enzyme-Linked ImmunoSorbent Assay (SSOP-ELISA) and PCR-Dot Blot were also optimized. The sensitivity and specificity of all six assays was then compared in a blind genotyping trial of 96 single insect samples that included a variety of kdr genotypes and African Anopheline species. The relative merits of each assay was assessed based on the performance in the genotyping trial, the length/difficulty of each protocol, cost (both capital outlay and consumable cost), and safety (requirement for hazardous chemicals). The real-time TaqMan assay was both the most sensitive (with the lowest number of failed reactions) and the most specific (with the lowest number of incorrect scores). Adapting the TaqMan assay to use a PCR machine and endpoint measurement with a fluorimeter showed a slight reduction in sensitivity and specificity. HRM initially gave promising results but was more sensitive to both DNA quality and quantity and consequently showed a higher rate of failure and incorrect scores. The sensitivity and specificity of AS-PCR, SSOP-ELISA, PCR Dot Blot and HOLA was fairly similar with a small number of failures and incorrect scores. The results of blind genotyping trials of each assay indicate that where maximum sensitivity and specificity are required the TaqMan real-time assay is the preferred method. However, the cost of this assay, particularly in terms of initial capital outlay, is higher than that of some of the other methods. TaqMan assays using a PCR machine and fluorimeter are nearly as sensitive as real-time assays and provide a cost saving in capital expenditure. If price is a primary factor in assay choice then the AS-PCR, SSOP-ELISA, and HOLA are all reasonable alternatives with the SSOP-ELISA approach having the highest throughput.

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Detection of knockdown resistance (kdr) mutations in Anopheles gambiae: a comparison of two new high-throughput assays with existing methods

The prospect of malaria eradication has been raised recently by the Bill and Melinda Gates Foundation with support from the international community. There are significant lessons to be learned from the major successes and failures of the eradication campaign of the 1960s, but cessation of transmission in the malaria heartlands of Africa will depend on a vaccine and better drugs and insecticides. Insect control is an essential part of reducing transmission. To date, two operational scale interventions, indoor residual spraying and deployment of long-lasting insecticide-treated nets (LLINs), are effective at reducing transmission. Our ability to monitor and evaluate these interventions needs to be improved so that scarce resources can be sensibly deployed, and new interventions that reduce transmission in a cost-effective and efficient manner need to be developed. New interventions could include using transgenic mosquitoes, larviciding in urban areas, or utilizing cost-effective consumer products. Alongside this innovative development agenda, the potential negative impact of insecticide resistance, particularly on LLINs, for which only pyrethroids are available, needs to be monitored.

Malaria Management: Past, Present, and Future

Background
Knock-down resistance (kdr) to DDT and pyrethroids in the major Afrotropical vector species, Anopheles gambiae sensu stricto, is associated with two alternative point mutations at amino acid position 1014 of the voltage-gated sodium channel gene, resulting in either a leucine-phenylalanine (L1014F), or a leucine-serine (L1014S) substitution. In An. gambiae S-form populations, the former mutation appears to be widespread in west Africa and has been recently reported from Uganda, while the latter, originally recorded in Kenya, has been recently found in Gabon, Cameroon and Equatorial Guinea. In M-form populations surveyed to date, only the L1014F mutation has been found, although less widespread and at lower frequencies than in sympatric S-form populations.

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Distribution of knock-down resistance mutations in Anopheles gambiae molecular forms in west and west-central Africa

Pyrethroid insecticide resistance in Anopheles gambiae sensu stricto is a major concern to malaria vector control programmes. Resistance is mainly due to target-site insensitivity arising from a single point mutation, often referred to as knockdown resistance (kdr). Metabolic-based resistance mechanisms have also been implicated in pyrethroid resistance in East Africa and are currently being investigated in West Africa. Here we report the co-occurrence of both resistance mechanisms in a population of An. gambiae s.s. from Nigeria. Bioassay, synergist and biochemical analysis carried out on resistant and susceptible strains of An. gambiae s.s. from the same geographical area revealed >50% of the West African kdr mutation in the resistant mosquitoes but <3% in the susceptible mosquitoes. Resistant mosquitoes synergized using pyperonyl butoxide before permethrin exposure showed a significant increase in mortality compared with the non-synergized. Biochemical assays showed an increased level of monooxygenase but not glutathione-S-transferase or esterase activities in the resistant mosquitoes. Microarray analysis using the An. gambiae detox-chip for expression of detoxifying genes showed five over-expressed genes in the resistant strain when compared with the susceptible one. Two of these, CPLC8 and CPLC#, are cuticular genes not implicated in pyrethroid metabolism in An. gambiae s.s, and could constitute a novel set of candidate genes that warrant further investigation.

Evidence of multiple pyrethroid resistance mechanisms in the malaria vector Anopheles gambiae sensu stricto from Nigeria.

Distribution of the molecular forms of Anopheles gambiae and pyrethroid knock down resistance gene in Nigeria.

The species composition of indoor and outdoor human-biting Anopheles mosquitoes and their relative contribution to Plasmodium falciparum transmission were determined for two communities in Ibadan, southwestern Nigeria where little or no data were available. Mosquitoes attracted to humans at night were caught in August, September and October 2000, coinciding with the peak malaria period in these areas. A total of 2176 Anopheles mosquitoes were collected, of which An. gambiae s.l. was predominant followed by An. Funestus and An. Hancocki. The results of PCR-based tests identified 58.8 % of the An. gambiae s.l. as An. gambiae s.s., and 41.2% as An. Arabiensis. The molecular (M and S) forms of An. gambiae s.s. were found in the ratio 1:3, respectively. A cocktail PCR-assay differentiated 65.6% of the An. Funestus group as An. funestus s.s., and 34.4% as An. Rivulorum. Outdoor biting mosquito numbers were significantly higher (P < 0.001) than that observed indoors. Peak indoor and outdoor biting activities of An. gambiae s.s. occurred at 01:00 and 24:00, respectively. The biting activities of An. funestus s.s. both indoors and outdoors attained a peak at 23h00 while An. Arabiensis and An. Rivulorum were more exophagic. The results of ELISA-based analyses indicated that An. gambiae s.s., An. Arabiensis and An. funestus s.s. serve as vectors in the area with an overall P. falciparum sporozoite infection rate of 5.6 %, 4.0% and 4.3 %, respectively. Both An. Rivulorum and An. Hancocki tested negative. The combined contribution of these mosquito species to malaria transmission in the study area highlights the inappropriateness of vector control strategies aimed at only one vector species.

Species composition and biting activities of anthropophilic Anopheles mosquitoes and their role in malaria transmission in a holo-endemic area of southwestern Nigeria

Nigeria has a high burden of vector borne diseases such as malaria and lymphatic filariasis (LF). This study aimed to determine the species composition of mosquitoes in Ibadan, Southwest Nigeria as well as determine their role in malaria and LF transmission. Adult mosquitoes were collected by Pyrethrum Spray Catch (PSC) and identified and graded according to their abdominal conditions. The mosquitoes were dissected to determine the parity status and to check for microfilariae of Wuchereria bancrofti. The presence of circumsporozoite protein of Plasmodium falciparum was examined using ELISA. A total of 1600 mosquitoes were collected of which 31 (1.9%) were Anopheles gambiae s.l. while 1756 (98%) were Culex sp. None of the mosquitoes examined was positive for Plasmodium falciparum and Wuchereria bancrofti. The lack of adequate sanitary conditions in the area could be responsible for the large number of mosquitoes collected. Health education could help in sensitizing the inhabitants.

https://www.entomoljournal.com/vol2Issue4/pdf/11.1.pdf

Species composition and temporal distribution of mosquito populations in Ibadan, Southwestern Nigeria.

This study was carried out to assess the resistance/susceptibility level of An. gambiae s.l, a major malaria vector in Ibadan metropolis, south west Nigeria, to two classes of insecticides approved by World Health Organization (WHO) for vector control. Anopheles larvae were collected from two communities (Ojoo and Bodija) within the metropolis and reared to adults. Two to three-day old, non-engorged female mosquitoes were exposed to discriminating dosages of 0.05% deltamethrin, 0.75% permethrin and 0.1% bendiocarb using WHO protocols and susceptibility test kits. Knockdown effect was recorded every 10 min and mortality scored 24 h after exposure. Species identification was by morphological characteristics only. The study revealed that the major malaria vector in Nigeria, An. gambiae s.l, were susceptible (mortality rate of 98.8%) to deltamethrin in Ojoo community, while Bodija recorded marginal susceptibility (87.5%). Both sites showed reduced susceptibility to permethrin and resistance to bendiocarb with 24 h post exposure mortalities ranging from 83.5 to 87.7% and 70.0 and 52.5%, respectively. The median Knockdown Time (KDT50) from 22-44.2 min for the pyrethroids (permethrin and deltamethrin), while that of carbamates (bendiocarb) range from 35.2 to 49.5 min. Resistance recorded in the field populations of An. gambiae s.l in Ibadan to bendiocarb was not observed in same population exposed to the pyrethroids (deltamethrin and permethrin) but with differential susceptibility. Therefore Bendiocarb may not be suitable as alternatives to mitigate pyrethroid resistance. A rationalised use of these insecticides coupled with regular monitoring of resistance status is essential to improve and evaluate the efficacy of the current vector control tools (ITN and IRS).

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Susceptibility of Anopheles gambiae sensu lato (Diptera: Culicidae) to Permethrin, Deltamethrin and Bendiocarb in Ibadan City, Southwest Nigeria

The nature and type of local indoor resting wall surfaces to certain level influences the residual bio-efficacy of insecticides used in indoor residual spraying programs. Knockdown and mortality ef...

https://journals.sagepub.com/doi/pdf/10.1177/1179543317732989

Kolade Tahiru Ibrahim

Papers

Distribution of the molecular forms of Anopheles gambiae and pyrethroid knock down resistance gene in Nigeria.

Species composition and biting activities of anthropophilic Anopheles mosquitoes and their role in malaria transmission in a holo-endemic area of southwestern Nigeria

Species composition and temporal distribution of mosquito populations in Ibadan, Southwestern Nigeria.

Susceptibility of Anopheles gambiae sensu lato (Diptera: Culicidae) to Permethrin, Deltamethrin and Bendiocarb in Ibadan City, Southwest Nigeria

Laboratory Evaluation of Residual Efficacy of Actellic 300 CS (Pirimiphos-Methyl) and K-Othrine WG 250 (Deltamethrin) on Different Indoor Surfaces.