Electroantennogram responses of the Triatoma dimidiata complex to volatiles produced by its exocrine glands

Resistance to deltamethrin in Triatoma infestans (Hemiptera: Reduviidae): does it influence the phenotype of antennae, wings, and heads?

In vector control terms, insecticide resistance is the development of the capacity, of an insect population, to tolerate doses of an insecticide that are lethal to most individuals in a typical population of the same species. The genetic changes that determine resistance may have adaptive costs in the resistant phenotype or, conversely, may result in an adaptive advantage when compared to susceptible insects in the environment without insecticides. Triatoma infestans is one of the main vectors of Trypanosoma cruzi in the southern cone of South America. High insecticide resistance in T. infestans was detected in Argentina in Salta and Chaco provinces. The objective of this study was to determine the possible morphometric changes in wings, heads, and the antennal phenotype of deltamethrin-resistant T. infestans (RR) males and females compared to susceptible insects (SS), evaluating its implication in adaptive processes such as olfactory capacity, dispersion, and probability of colonizing new habitats, among others. Nine type I landmarks were marked on wings, 5 type II landmarks on heads, and 10 antennal sensilla were counted on 106 adults of both sexes (resistant and susceptible from first and second laboratory generations). Morphological divergence was observed between the two groups (RR and SS). The RR insects showed smaller sizes of wings and heads and shape compatible with lower dispersal potential and different active dispersal behaviors. Antennae also revealed sensory simplification in RR and divergence between RR and SS, although more marked in females. This study characterizes for the first time T. infestans RR and SS through wings, heads, and antennae. The results suggest a lower dispersive potential in resistant insects and the differences described lay the foundations for the identification of a resistance biomarker in triatomines.

Dog hair volatiles attract Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) females

Rhipicephalus sanguineus sensu lato (s.l.) (Latreille) feeds on domestic dogs worldwide. This tick species uses dog volatiles during host-seeking behavior. In this study, we identified volatile compounds from dog hairs involved in the host location of R. sanguineus s.l. The R. sanguineus s.l. females, but not males, were attracted to hair samples and Super Q extracts from Schnauzer dogs in Y-tube olfactometer bioassays. A total of 54 compounds from dog hair extracts were identified by gas chromatography coupled to mass spectrometry, including hydrocarbons, aldehydes, alcohols, ketones, and carboxylic acids. Screening the identified compounds by the single sensillum recording technique showed that isovaleric acid, hexanal, heptanal, and sucaltone (6-methyl-5-hepten-2-one) significantly stimulated the olfactory receptor neurons of the basiconic, chaeticum, and trichodeum sensilla of female ticks. When synthetic compounds were evaluated alone, or in binary, tertiary, or quaternary mixtures, female ticks were only attracted to isovaleric acid and 1 tertiary mixture (hexanal, heptanal, and isovaleric acid). We conclude that isovaleric acid functions as an attractant for R. sanguineus s.l. These findings contribute to the understanding of the chemical ecology of ticks during host location.

Does Trypanosoma cruzi (Chagas, 1909) (Kinetoplastida: Trypanosomatidae) modify the antennal phenotype of Triatoma dimidiata (Latreille, 1811) (Hemiptera: Triatominae)?

Background

Triatoma dimidiata is a vector of the protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease. Phenotypic plasticity allows an organism to adjust its phenotype in response to stimuli or environmental conditions. Understanding the effect of T. cruzi on the phenotypic plasticity of its vectors, known as triatomines, has attracted great interest because of the implications of the parasite–triatomine interactions in the eco-epidemiology and transmission of the etiologic agent of Chagas disease. We investigated if the infection of the vector with T. cruzi may be associated with a change in the antennal phenotype of sylvatic, domestic, and laboratory-reared populations of T. dimidiata.

Methods

The abundance of each type of sensillum (bristles, basiconic, thick- and thin-walled trichoid) on the antennae of T.cruzi-infected and non-infected T.dimidiata reared in the laboratory or collected in sylvatic and domestic ecotopes were measured under light microscopy and compared using Kruskal–Wallis non-parametric tests and permutational multivariate analysis of variance.

Results

We found significant differences between sensilla patterns of infected and non-infected insects within sylvatic and domestic populations. Conversely, we found no significant differences between sensilla patterns of infected and non-infected insects within the laboratory-reared population. Besides, for sylvatic and domestic populations, sexual dimorphism tended to be increased in infected insects.

Conclusion

The differences observed in infected insects could be linked to higher efficiency in the perception of odor molecules related to the search for distant mates and hosts and the flight dispersal in search of new habitats. In addition, these insects could have a positive effect on population dynamics and the transmission of T.cruzi.

Graphical Abstract

Isolation and Identification of Volatile Substances with Attractive Effects on Wohlfahrtia magnifica from Vagina of Bactrian Camel

Vaginal myiasis is one of the most serious parasitic diseases in Bactrian camels. At present, there are no reports on biological control measures of the disease. In this paper, the metabolomic analysis of vaginal secretions from susceptible and non-susceptible camels was performed by ACQUITY UPLC H-Class Ultra Performance Liquid Chromatograph. The results matched in 140 vaginal compounds. Methylheptenone, 1-octen-3-ol, and propyl butyrate and their mixtures were selected for gas chromatography-electroantennography (GC-EAD), electroantennography (EAG), behavioral experiments and trapping experiments of Wohlfahrtia magnifica (W. magnifica). Results showed that the W. magnifica had EAG responses to the three compounds, respectively. The EAG responses of female flies to different concentrations of methylheptenone were significantly different, but to the others had no significant difference, and there was no significant difference in the same compounds between the different sexes. Behavioral and trapping experiments showed that methylheptenone and 1-octen-3-ol have significant attraction to W. magnifica, but there was no significant difference to propyl butyrate. When methylheptenone and 1-octen-3-ol were mixed in different proportions, it was found that a mixture at the ratio of 1:1 and 0.5:1 had extremely significant and significant attraction, respectively, to both male and female W. magnifica. The study showed that, except for propyl butyrate, the higher the concentrations of the other two compounds, the stronger the attractivity to the W. magnifica, and a mixture at the ratio of 1:1 could enhance the attractivity to the W. magnifica.

Signs of Urban Evolution? Morpho-Functional Traits Co-variation Along a Nature-Urban Gradient in a Chagas Disease Vector

Environmental change (i.e., urbanization) impacts species in contrasting ways, with some species experiencing benefits given their way of life (i.e., blood-sucking insects). How these species respond to such change is not well understood and for species involved in human diseases, this “how” question is particularly important. Most Triatominae bug species inhabit tropical and subtropical forests where their vertebrate hosts’ temporal abundance depends on climate seasonality. However, in human encroached landscapes, triatomines can benefit from resource stability which may lead to adaptive phenotypic change to track novel hosts. We tested for an association between different landscapes and morpho-functional traits linked to sensory, motion, and feeding functions in Triatoma dimidiata and compared fecundity (i.e., number of eggs) in each landscape as a proxy of fitness. Using geometric and traditional morphometric tools, we predicted a morphological simplification in bugs inhabiting urbanized areas. While wing morphology or proboscis were not influenced by landscape class, the opposite occurred for thorax morphology and number of sensilla. Wing and thorax morphology did not covary under modified landscape scenarios, yet we detected a morpho-functional convergence for thorax size and antennal phenotype in both sexes, with a simplification trend, from nature to urban settings. Given no fecundity differences across landscapes, there is no potential reproductive costs. Moreover, the convergence of thorax size and antennal phenotype suggests differences in flight/locomotion performance and host/environment perception, as a possible adaptive response to relaxed selective pressures of the bug’s native habitat. These results imply that T. dimidiata could be adapting to urbanized areas.

Comparative Study of the Antennal Phenotype in Species of the Belminus (Hemiptera: Triatominae) Genus Using Optical and Scanning Electron Microscopy

The genus Belminus Stål, 1859 is distinguished by markedly entomophagous species. This genus is a poorly studied group of the Triatominae (Jeannel, 1919), which includes hematophagous species that are vectors of Trypanosoma cruzi (Chagas, 1909), the etiological agent of Chagas disease. This study reports for the first time the description of the antennal sensilla of Belminus corredori (Galvão & Angulo, 2003), Belminus herreri (Lent & Wygodzinsky, 1979), and Belminus ferroae (Sandoval, Pabón, Jurberg & Galvão, 2007) nymphs and adults throughout scanning electron microscopy and optical microscopy. Nine morphological types of sensilla were identified in the three species, including bristles I and II, trichobothria, tapered hairs, thin-walled trichoid, thick-walled trichoid, basiconic, campaniform, and coeloconica sensilla. The analysis of the most abundant types of sensilla and their distribution in nymphs and adults shows similarities with the antennal phenotypes described in other Triatominae. Quantitative differences showed the important phenotypic plasticity of this morphological trait in the genus and allowed for the separation of the species in both sexes. These differences were associated with sexual dimorphism and wing condition (macropterous and brachypterous). The role of the antennal phenotype in sexual behavior, its usefulness as a taxonomic tool, and its relationship with the dispersal capacity of these species are discussed.