Effect of two commercial herbicides on life history traits of a human disease vector, Aedes aegypti, in the laboratory setting

Exposure to copper metal enhances the tolerance of An. gambiae s.s. over multiple generations while reducing both fertility and fecundity in this primary malaria vector

Background

Anopheles s.l. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness. This study investigated the larval metal exposure on larval development and reproduction of An. gambiae s.s., a laboratory susceptible strain, kisumu.

Methods

Stage 2 larvae of Anopheles gambiae, Kisumu were exposed to C 1 = 484 μg L -1, C 2 = 300 μg L -1 and 0 μg L -1 (control) of copper chloride. Larval mortality, pupation time, pupation rate, gonotrophic cycle length, fecundity and fertility of larvae/adults were assessed over six generations.

Results

Results revealed that larval mortality rate was significantly higher in the C 1 groups of each group (p = 0.000), but this mortality rate decreased over generations. Pupation time was extended to 13 and 14 days respectively for C 2 and C 1 groups (p = 0.000) compared to the control group. Similar results were observed for the gonotrophic cycle, which increased from 4 days at G0 to more than 6 days at generation 5 in adults of C 1. The pupation rate in generation 4 (C 1) and generation 5 of the same group (p = 0.000) as well as the emergence rate in generation 4 (C 2, p = 0.000) and generation 5 (C 1 and C 2, p = 0.000) decreased significantly compared to the control group. The average number of eggs laid was lower in the test groups from generation 4 to generation 5 (C 1 and C 2, p = 0.00) and egg fertility was also negatively affected by exposure of the larval stage of An. gambiae s.s. to copper.

Conclusion

This study showed that copper not only exhibits larvicidal properties in Anopheles gambiae s.s. larvae, it also revealed the potential of this metal to reduce fecundity and fertility in these malaria vectors.

Impact of Human Activities on Disease-Spreading Mosquitoes in Urban Areas

Urbanization is one of the leading global trends of the twenty-first century that has a significant impact on health. Among health challenges caused by urbanization, the relationship of urbanization between emergence and the spread of mosquito-borne infectious diseases (MBIDs) is a great public health concern. Urbanization processes encompass social, economic, and environmental changes that directly impact the biology of mosquito species. In particular, urbanized areas experience higher temperatures and pollution levels than outlying areas but also favor the development of infrastructures and objects that are favorable to mosquito development. All these modifications may influence mosquito life history traits and their ability to transmit diseases. This review aimed to summarize the impact of urbanization on mosquito spreading in urban areas and the risk associated with the emergence of MBIDs. Moreover, mosquitoes are considered as holobionts, as evidenced by numerous studies highlighting the role of mosquito-microbiota interactions in mosquito biology. Taking into account this new paradigm, this review also represents an initial synthesis on how human-driven transformations impact microbial communities in larval habitats and further interfere with mosquito behavior and life cycle in urban areas.

Roundup negatively impacts the behavior and nerve function of the Madagascar hissing cockroach (Gromphadorhina portentosa)

Glyphosate is the active ingredient in Roundup formulations. Glyphosate-based herbicides are used globally in agriculture, forestry, horticulture, and in urban settings. Glyphosate can persist for years in our soil, potentially impacting the soil-dwelling arthropods that are primary drivers of a suite of ecosystem services. Furthermore, although glyphosate is not generally classified as neurotoxic to insects, evidence suggests that it may cause nerve damage in other organisms. In a series of experiments, we used food to deliver environmentally realistic amounts of Roundup ready-to-use III, a common 2% glyphosate-based herbicide formulation that lists isopropylamine salt as its active ingredient, to Madagascar hissing cockroaches. We then assessed the impact of contamination on body mass, nerve health, and behavior. Contaminated food contained both 30.6 mg glyphosate and so-called inert ingredients. Food was refreshed weekly for 26-60 days, depending on the experiment. We found that consumption of contaminated food did not impact adult and juvenile survivorship or body weight. However, consumption of contaminated food decreased ventral nerve cord action-potential velocity by 32%, caused a 29% increase in respiration rate, and caused a 74.4% decrease in time spent on a motorized exercise wheel. Such changes in behavior may make cockroaches less capable of fulfilling their ecological service, such as pollinating or decomposing litter. Furthermore, their lack of coordination may make them more susceptible to predation, putting their population at risk. Given the decline of terrestrial insect abundance, understanding common risks to terrestrial insect populations has never been more critical. Results from our experiments add to the growing body of literature suggesting that this popular herbicide can act as a neurotoxin.

Container Type Affects Mosquito (Diptera: Culicidae) Oviposition Choice

Larvae of container-breeding mosquitoes develop in a wide range of container habitats found in residential neighborhoods. Different mosquito species may exhibit preference for different container types and sizes. Due to phenological differences, species composition in container habitats may change over time. We first conducted weekly neighborhood container surveys to determine the types of container habitats found in residential neighborhoods, and to determine mosquito species composition over time within these habitats. We then conducted an oviposition choice field assay to determine whether female mosquitoes of different species preferentially oviposit in different container types commonly found in neighborhoods. Halfway through the experiment, the largest container was removed at half the sites to test the hypothesis that incomplete source reduction alters oviposition preference among the remaining containers. In the neighborhood surveys, large containers had the greatest mosquito densities and the highest species richness. Aedes albopictus (Skuse), the most commonly collected mosquito, was found in all container types. The oviposition experiment indicated that Culex spp. females preferentially oviposit in large containers. When the largest container was removed, the total number of egg rafts decreased. Aedes spp. females preferred to oviposit in large- and medium-sized containers, but the total number of eggs laid did not change when the large container was removed. These results confirm that understanding habitat preferences of container-breeding mosquitoes is important to control efforts targeting vector species and that incomplete removal of container habitats may have unpredictable consequences for the distribution of juveniles among remaining habitats.

Impact of field-realistic doses of glyphosate and nutritional stress on mosquito life history traits and susceptibility to malaria parasite infection

Glyphosate is the world's most widely used herbicide. The commercial success of this molecule is due to its nonselectivity and its action, which would supposedly target specific biosynthetic pathways found mainly in plants. Multiple studies have however provided evidence for high sensitivity of many nontarget species to glyphosate and/or to formulations (glyphosate mixed with surfactants). This herbicide, found at significant levels in aquatic systems through surface runoffs, impacts life history traits and immune parameters of several aquatic invertebrates' species, including disease-vector mosquitoes. Mosquitoes, from hatching to emergence, are exposed to aquatic chemical contaminants. In this study, we first compared the toxicity of pure glyphosate to the toxicity of glyphosate-based formulations for the main vector of avian malaria in Europe, Culex pipiens mosquito. Then we evaluated, for the first time, how field-realistic dose of glyphosate interacts with larval nutritional stress to alter mosquito life history traits and susceptibility to avian malaria parasite infection. Our results show that exposure of larvae to field-realistic doses of glyphosate, pure or in formulation, did not affect larval survival rate, adult size, and female fecundity. One of our two experimental blocks showed, however, that exposure to glyphosate decreased development time and reduced mosquito infection probability by malaria parasite. Interestingly, the effect on malaria infection was lost when the larvae were also subjected to a nutritional stress, probably due to a lower ingestion of glyphosate.

Exposure to Roundup® affects behaviour, head regeneration and reproduction of the freshwater planarian Girardia tigrina

The demand of glyphosate-based herbicides including Roundup® is rising in the tropics due to increase occurence of glyphosate-resistant weeds that require higher herbicide application rates but also because of their use associated with genetically engineered, glyphosate-tolerant crops. Consequently, there is now an excessive use of glyphosate in agricultural areas with potential adverse effects also for the surrounding aquatic environments. This study aimed to determine the sensitivity of the freshwater planarian Girardia tigrina to acute and chronic exposures of Roundup®. Planarians were exposed to a range of lethal and sub-lethal concentrations of Roundup® to determine the median lethal concentration (LC50) concerning its active ingredient glyphosate and also effects on locomotor velocity (pLMV), feeding rate, regeneration, reproductive parameters and morphological abnormalities. Regeneration endpoints included length of blastema and time for photoreceptors and auricles regeneration after decapitation, while effects on reproduction were assessed measuring fecundity (number of deposited cocoons) and fertility (number of hatchlings) over five weeks of exposure to glyphosate. The estimated 48 h LC50 of was 35.94 mg glyphosate/L. Dose dependent effects were observed for feeding, locomotion and regeneration endpoints with Lowest observed effect concentration (LOEC) values as low as 3.75 mg glyphosate/L. Chronic exposures to environmentally relevant concentrations of glyphosate significantly impaired fecundity and fertility rates of exposed planarians (median effective concentration, EC50 = 1.6 mg glyphosate/L for fecundity and fertility rates). Our results show deleterious effects of Roundup® on regeneration, behavior and reproduction of freshwater planarians and add important ecotoxicological data towards the environmental risk assessment of glyphosate-based herbicide in freshwater ecosystems.

The effect of commercial herbicide exposure on the life history and insecticide resistance phenotypes of the major malaria vector Anopheles arabiensis (Diptera: culicidae)

Herbicides, such as atrazine and glyphosate, are common agrochemicals known to pollute surface ground water. As such, aquatic invertebrates associated with agricultural activities can be exposed to varying doses of these xenobiotics. Anopheles arabiensis, a major malaria vector species in southern Africa, is often closely associated with agricultural activities. This study aimed to examine the effects of larval atrazine or glyphosate exposure on larval and adult life history traits on two laboratory strains of An. arabiensis; one insecticide susceptible (SENN), the other selected for resistance (SENN DDT). Atrazine delayed time to pupation in both strains, but markedly more so in SENN DDT. Glyphosate treatment reduced time to pupation in SENN DDT. Larval atrazine exposure decreased adult longevity in SENN, while both herbicide treatments significantly increased adult longevity in SENN DDT. Larval glyphosate exposure was the more potent enhancer of insecticide tolerance in adult mosquitoes. In SENN DDT, it reduced deltamethrin and malathion-induced mortality, and the LT50 s for these insecticides were increased in association with herbicide exposure. Glyphosate exposure also increased the LT50 s for malathion and deltamethrin in SENN. Exposure to both herbicides had contrasting effects on detoxification enzyme activities. Although both increased cytochrome P450 activity, they had opposite effects on those enzymes involved in reactive oxygen species detoxification. Glyphosate decreased glutathione S-transferase activity, but increased catalase activity with atrazine having the opposite effect. This study demonstrates that larval exposure to the herbicides atrazine and glyphosate can affect the insecticide susceptibilities and life history traits of epidemiological importance in An. arabiensis, with glyphosate being the more potent effector of insecticide resistance.