Biology subjects

Schal, C.

Publications and source records attributed to Schal, C..

9 recordsLinked to original sources

bioRxiv2026

Efficacy of an attractive lethal ovitrap to reduce populations of Aedes mosquitoes: a controlled trial in Iquitos, Peru

IntroductionDengue, one of the most important arboviral infections worldwide, is transmitted primarily by the mosquito Aedes aegypti, a vector closely associated with human habitations. Because vector control is the primary prevention strategy for this disease novel tools are urgently needed. We evaluated an Attractive Lethal OviTrap (ALOT) that targets epidemiologically relevant gravid female mosquitoes for public health impact against dengue disease. MethodsWe conducted a proof-of-concept field efficacy trial in the Amazonian city of Iquitos, Peru, to quantify the reduction of vector density, parity, and sex ratio and symptomatic human dengue infection over a 3.5 year follow-up period. After three baseline entomological surveys in core (753 houses), and buffer (1,549 houses) areas where traps were placed in and around homes, and a control (1,233 houses) area without traps, entomological surveys were carried out every 2 months, and household residents were monitored for dengue disease 3 times a week. Trap maintenance was conducted at 2-3 week intervals by study staff during the first 2.5 years and by residents in the final year. ResultsTotal and female Ae. aegypti abundance demonstrated a strong initial effect with 52% and 47% fewer mosquitoes after trap placement, respectively (Total: RR = 0.48, 95% CI: 0.40 - 0.58, p < 0.001; Females: RR = 0.53, 95% CI: 0.43 - 0.66, p < 0.001). The effect diminished significantly, however, over the study period (interaction coefficient = 0.035 per month, p < 0.001; interaction coefficient = 0.030 per month, p < 0.001). Female-to-male ratio decreased after trap deployment and impact on non-Aedes abundance was like that of Aedes. Cumulative symptomatic dengue incidence was 1.40% (95% CI: 1.00%-1.70%) in the ALOT area versus 3.20% (95% CI: 2.60%-3.80%) in the control area, a 56% relative reduction (log-rank {chi}{superscript 2}=30.0, p<0.001). Restricted mean survival time analysis showed participants in the intervention area on average remained dengue-free for 15.5 additional days (95% CI: 11.1-20.0, p<0.001). ConclusionsThe ALOT strategy functioned as predicted, decreasing but not eliminating female vector densities, with a clear public health impact, lowering dengue disease in areas where traps were deployed. Our study also illustrates the challenges associated with conducting large-scale vector control trials and the need to consider programmatic implementation early in the process of bringing a new product to market. Author SummaryDengue is one of the most important mosquito transmitted infections worldwide. Aedes aegypti, the most important species involved, has a unique biology living in containers associated with households. New methods to control this mosquito are needed and we present our evaluation of a novel trap called the Attractive Lethal OviTrap (ALOT) that targets older female mosquitoes that are the most important for dengue disease transmission. We conducted a trial in the Amazonian city of Iquitos, Peru, to measure reductions in mosquito numbers, age, and sex ratio and symptomatic human dengue infections over a 3.5 years. After baseline entomological surveys prior to placing ALOT traps in homes in a treatment area, which included a central core area with 753 houses and a protective buffer area with 1,549 houses areas. We also had a control area without any traps in 1,233 houses. Mosquito surveys were carried out every 2 months, and household residents were monitored for dengue disease 3 times per week. Trap maintenance was conducted at 2 - 3 week intervals by study staff during the first 2.5 years and by residents in the final year. The number of all Ae. aegypti were initially reduced by 52% after trap placement whereas females were reduced by 47%. The effect diminished significantly, however, over the study period. Female-to-male ratio decreased after trap deployment and impact on other mosquito species was like that of Aedes. Dengue incidence was 56% less in the area with traps compared to the control area, estimating that participants in the intervention area on average remained dengue-free for 15.5 additional days. The ALOT strategy functioned as predicted, decreasing but not eliminating female mosquitos and had a clear public health impact, lowering dengue disease in areas where traps were deployed. Our study also illustrates the challenges associated with conducting large-scale vector control trials and the need to consider programmatic implementation early in the process of bringing a new product to market.

ecology↗

bioRxiv2024

Lethal Disruption of the Symbiotic Gut Community in Eastern Subterranean Termite Caused by Boric Acid

AbstractThe Eastern subterranean termite, Reticulitermes flavipes (Kollar), is a significant pest, causing extensive damage to structures that amount to substantial economic losses. Traditional termite control methods have utilized boric acid, known for its broad-spectrum insecticidal properties, yet its impact on termite gut microbiomes and the implications of such effects remain understudied. Our study evaluates the dose-dependent mortality of R. flavipes upon being provided boric acid treated filter papers and investigates the resulting dysbiosis within the termite gut microbiome. Consistent with reports from other insects, mortality increased in a dose-dependent manner, with the highest boric acid concentration (203.7 {micro}g/cm2 of filter paper) significantly reducing termite survival. 16S rRNA gene sequencing of the gut microbiome revealed notable shifts in composition, indicating boric acid-induced dysbiosis. Aside from an overall decrease in microbial diversity, the relative abundance of some symbionts essential for termite nutrition decreased in response to higher boric acid concentrations, while several putative pathogens increased. Our findings extend the understanding of boric acids mode of action in termites, emphasizing its effect beyond direct toxicity to include significant microbiome modulation that can have dire effects on termite biology. Considering its potential to induce dysbiosis and potentially augment the effectiveness of entomopathogens, our study supports the continued use of boric acid and related compounds for termite-resistant treatments for wood.

zoology↗

bioRxiv2024

Deployment and transcriptional evaluation of nitisinone, an FDA-approved drug, to control bed bugs

Bed bugs are blood-feeders that rapidly proliferate into large indoor infestations. Their bites can cause allergies, secondary infections and psychological stress, among other problems. Although several tactics for their management have been used, bed bugs continue to spread worldwide wherever humans reside. This is mainly due to human-mediated transport and their high resistance to several classes of insecticides. New treatment options with novel modes of action are required for their control. In this study, we evaluated the use of nitisinone (NTBC), an FDA-approved drug, for bed bug control in an insecticide-susceptible (HH) and an insecticide-resistant (CIN) population. Although NTBC was lethal to both populations when administered orally or applied topically in very low doses, we observed a slight but significant resistance in the CIN population. Transcriptomic analysis in both populations indicated that NTBC treatment elicited a broad suppression of genes associated with RNA post-transcriptional modifications, translation, endomembrane system, protein post-translational modifications and protein folding. The CIN population exhibited higher ATP production and xenobiotic detoxification. Feeding studies on a mouse model highlight that NTBC could be used as a control method of bed bugs by host treatment. The results demonstrate that NTBC can be used as a new active ingredient for bed bug control by topical or oral treatment and shed light on the molecular mechanisms of suppressed tyrosine metabolism following NTBC treatment.

physiology↗

bioRxiv2021

Modulation of fatty acid elongation generates sexually dimorphic hydrocarbons and female attractiveness in Blattella germanica (L.)

Insect cuticular hydrocarbons (CHCs) serve as important intersexual signaling chemicals and generally show variation between the sexes, but little is known about the generation of sexually dimorphic hydrocarbons (SDHCs) in insects. Here, we report the molecular mechanism and biological significance that underling the generation of SDHC in the German cockroach, Blattella germanica. Sexually mature females possess more C29 cuticular hydrocarbons (CHCs), especially the contact sex pheromone precursor 3,11-DimeC29. RNAi screen against fatty acid elongase gene family members and combined with heterologous expression revealed that both BgElo12 and BgElo24 were involved in HC production, but BgElo24 is of wide catalytic activities and is able to provides substrates for BgElo12, and only the female-enriched BgElo12 was responsible for sustaining female-specific HC profile. Repressing BgElo12 masculinized the female CHC profile, decreased contact sex pheromone level and consequently reduced the sexual attractiveness of female cockroaches. Moreover, the asymmetric expression of BgElo12 between the sexes is modulated by sex differentiation cascade. Specifically, male-specific BgDsx represses the transcription of BgElo12 in males, while BgTra is able to remove this effect in females. Our study reveals a novel molecular mechanism responsible for the formation of SDHCs, and also provide evidences on shaping of the SDHCs by sexual selection, as females use them to generate high levels of contact sex pheromone.

molecular biology↗

bioRxiv2020

Mating and starvation modulate feeding and host-seeking responses in female bed bugs, Cimex lectularius

Adaptive insect behavior is subject to modulation by internal physiological states and external social contexts to enhance reproductive fitness and survival. The common bed bug, Cimex lectularius is an obligate hematophagous ectoparasite that requires host blood for growth, development, and reproduction. We investigated how mating, starvation and social factors such as harassment by males affect host-seeking, blood feeding, oviposition, and survival of female bed bugs. The percentage of females that fed and the amount of blood they ingested were greater in mated females (90-100%) than in unmated females (48-60%). Mating state also modulated the females orientation towards human skin odor in an olfactometer; more mated (69%) than unmated (23%) females responded to human odors. The response rate of unmated females (60%) to human odor increased with longer starvation period, while the opposite pattern was observed in mated females (20%). Although fecundity after a single blood meal was unaffected by long or short residence with males, females subjected to frequent copulations had lower survivorship and lifespan than females subjected to males for only 24 h. Taken together, these results indicate that behaviors are adaptively expressed based on the internal physiological state to maximize survival and reproductive fitness.

animal behavior and cognition↗

bioRxiv2019

Environmental decomposition of cuticular hydrocarbons generates a volatile pheromone that guides insect social behavior

Once emitted, semiochemicals are exposed to reactive environmental factors that may alter them, thus disrupting chemical communication. Some species, however, might have adapted to detect environmentally mediated breakdown products of their natural chemicals as semiochemicals. We demonstrate that air, water vapor, and ultraviolet (UV) radiation break down unsaturated cuticular hydrocarbons (CHCs) of Periplaneta americana (American cockroach), resulting in the emission of volatile organic compounds (VOCs). In behavioral assays, nymphs strongly avoided aggregating in shelters exposed to the breakdown VOCs from cuticular alkenes. The three treatments (air, water vapor, UV) produced the same VOCs, but at different time-courses and ratios. Fourteen VOCs from UV-exposed CHCs elicited electrophysiological responses in nymph antennae; 10 were identified as 1-pentanol, 1-octanol, 1-nonanol, tetradecanal, acetic acid, propanoic acid, butanoic acid, pentanoic acid and hexanoic acid. When short-chain fatty acids were tested as a mix and a blend of the alcohols and aldehyde was tested as a second mix, nymphs exhibited no preference for control or treated shelters. However, nymphs avoided shelters that were exposed to VOCs from the complete 10-compound mix. Conditioned shelters (occupied by cockroaches with feces and CHCs deposited on the shelters), which are normally highly attractive to nymphs, were also avoided after UV-exposure, confirming that breakdown products from deposited metabolites, including CHCs, mediate this behavior. Our results demonstrate that common environmental and anthropogenic agents degrade CHCs into volatile semiochemicals that may serve as necromones or epideictic pheromones, mediating group formation and dissolution.\n\nSignificance StatementCuticular hydrocarbons (CHCs) cover the outer surface of insects, where they prevent water loss and serve as sex pheromones and in nest-mate recognition in social insects. Although CHCs are not volatile, they can be broken into volatile fragments by reacting with environmental agents. We demonstrate that volatile breakdown products of CHCs affect the social behavior of the American cockroach. A synthetic mix of volatiles dispersed cockroaches away from shelters, signaling an unsuitable shelter. These results highlight that some insect species have evolved communication strategies that exploit environmental and anthropogenic agents to produce bioactive compounds that mediate ecological interactions.

ecology↗

bioRxiv2019

Hemimetabolous insects elucidate the origin of sexual development via alternative splicing

Insects are the only animals in which sexual differentiation is controlled by sex-specific RNA splicing. The doublesex (dsx) transcription factor produces distinct male and female protein isoforms (DsxM and DsxF) under the control of the RNA splicing factor transformer (tra). tra itself is also alternatively spliced so that a functional Tra protein is only present in females; thus, DsxM is produced by default, while DsxF expression requires Tra. The sex-specific Dsx isoforms are essential for both male and female sexual differentiation. This pathway is profoundly different from the molecular mechanisms that control sex-specific development in other animal groups. In animals as different as vertebrates, nematodes, and crustaceans, sexual differentiation involves male-specific transcription of dsx-related transcription factors that are not alternatively spliced and play no role in female sexual development. To understand how the unique splicing-based mode of sexual differentiation found in insects evolved from a more ancestral transcription-based mechanism, we examined dsx and tra expression in three basal, hemimetabolous insect orders. We find that functional Tra protein is limited to females in the kissing bug Rhodnius prolixus (Hemiptera), but is present in both sexes in the louse Pediculus humanus (Phthiraptera) and the cockroach Blattella germanica (Blattodea). Although alternatively spliced dsx isoforms are seen in all these insects, they are sex-specific in the cockroach and the kissing bug but not in the louse. In B. germanica, RNAi experiments show that dsx is necessary for male, but not female, sexual differentiation, while tra controls female development via a dsx-independent pathway. Our results suggest that the distinctive insect mechanism based on the tra-dsx splicing cascade evolved in a gradual, mosaic process: sex-specific splicing of dsx predates its role in female sexual differentiation, while the role of tra in regulating dsx splicing and in sexual development more generally predates sex-specific expression of the Tra protein. We present a model where the canonical tra-dsx axis originated via merger between expanding dsx function (from males to both sexes) and narrowing tra function (from a general splicing factor to the dedicated regulator of dsx).

developmental biology↗

bioRxiv2018

Queen and king recognition in the subterranean termite, Reticulitermes flavipes: Evidence for royal recognition pheromones

Royal recognition is a central feature of insect societies, allowing them to maintain the reproductive division of labor and regulate colony demography. Queen recognition has been broadly demonstrated and queen recognition pheromones have been identified in social hymenopterans, and in one termite species. Here we describe behaviors that are elicited in workers and soldiers by neotenic queens and kings of the subterranean termite, Reticulitermes flavipes, and demonstrate the chemical basis for the behavior. Workers and soldiers readily perform a lateral or longitudinal shaking behavior upon antennal contact with queens and kings. When royal cuticular chemicals are transferred to live workers or inert glass dummies, they elicit antennation and shaking in a dose-dependent manner. The striking response to reproductives and their cuticular extracts suggests that royal-specific cuticular compounds act as recognition pheromones and that shaking behavior is a clear and measurable queen and king recognition response in this termite species.

animal behavior and cognition↗

bioRxiv2017

Hemimetabolous genomes reveal molecular basis of termite eusociality

Around 150 million years ago, eusocial termites evolved from within the cockroaches, 50 million years before eusocial Hymenoptera, such as bees and ants, appeared. Here, we report the first, 2GB genome of a cockroach, Blattella germanica, and the 1.3GB genome of the drywood termite, Cryptotermes secundus. We show evolutionary signatures of termite eusociality by comparing the genomes and transcriptomes of three termites and the cockroach against the background of 16 other eusocial and non-eusocial insects. Dramatic adaptive changes in genes underlying the production and perception of pheromones confirm the importance of chemical communication in the termites. These are accompanied by major changes in gene regulation and the molecular evolution of caste determination. Many of these results parallel molecular mechanisms of eusocial evolution in Hymenoptera. However, the specific solutions are remarkably different, thus revealing a striking case of convergence in one of the major evolutionary transitions in biological complexity.

evolutionary biology↗