Culex mosquitoes (Diptera: Culicidae) egg laying in traps loaded with Bacillus thuringiensis variety israelensis and baited with skatole

Semiochemical based integrated livestock pest control

The role of arthropods as livestock pests has been well established. Besides their biting habits causing nuisance in animals; they are important vectors for transmission of economically important livestock diseases worldwide. Various pests and vector control managemental programs that also make use of chemicals have variable success rates. Consequently, insecticide/acaricide resistance has been reported against most of the commonly used chemicals along with increased concern for environment and demand for clean and green, residue-free animal products. This calls for an urgent need to develop novel, alternate, effective strategies/technologies. This lays the foundation for the use of semiochemicals as alternatives along with other biological control agents. Current knowledge on semiochemical use in livestock is refined and limited; however, it has been widely exploited in the agricultural sector to control plant and food crop pests, surveillance, and monitoring. Semiochemicals have an added advantage of being natural and safe; however, knowledge of extraction and quantification by using assays needs to be explicit. Expertise is required in behavioral and electrophysiological studies of arthropods and their interactions with the host and environment targeting specific semiochemicals for promising results. A thorough prior understanding on aspects such as mechanism of action, the stimulus for the release, the effecter/target species, response produced, application methods, dose and concentration is required to develop any successful pest/vector control program. The current review provides essential and frontline information on semiochemicals and their potential applications in the livestock sector along with future challenges and interventions.

Synergism between nonane and emanations from soil as cues in oviposition-site selection of natural populations of Anopheles gambiae and Culex quinquefasciatus

BACKGROUND

Olfactory cues have been shown to have an important role in guiding gravid mosquito females to selected sites for egg laying. The objective of this study was to determine the influence of emanations from soil from a breeding site and the putative oviposition pheromone nonane on oviposition-site selection of natural populations of Anopheles gambiae sensu lato (s.l.) and Culex quinquefasciatus.

METHODS

This field-based study was conducted in Mvomero District in East-central Tanzania. In a dual-choice experimental set up, clay bowls were dug into the ground and filled with one of the following treatments: (i) distilled water + autoclaved soil (control), (ii) distilled water + soil from a natural mosquito breeding site, (iii) distilled water + nonane and (iv) distilled water + nonane + soil from a natural breeding site. Soil was dried and autoclaved or dried only before use. After five days of incubation, larvae were collected daily for 10 days. The median number of larvae per bowl per day was used as outcome measure.

RESULTS

Autoclaved soil had a significant attractive effect on oviposition behaviour of Cx. quinquefasciatus (median values ± s.e: 8.0 ± 1.1; P < 0.005) but no effect on An. gambiae (median value ± s.e: 0.0 ± 0.2; P = 0.18). Nonane and emanations from untreated soil significantly and positively influenced the selection of oviposition sites by both An. gambiae s.l. (median values ± s.e.: 12.0 ± 2.0 and 4.5 ± 1.5, respectively; P < 0.0001) and Cx. quinquefasciatus (median values ± s.e.: 19.0 ± 1.3 and 17.0 ± 2.0, respectively; P < 0.0001). A mixture of nonane and untreated soil caused a synergistic effect on oviposition behaviour in An. gambiae s.l. (median value ± s.e.: 23.5 ± 2.5; P < 0.0001) compared to either nonane (median values ± s.e.: 12.0 ± 2.0; P < 0.0001) or untreated soil alone (median value ± s.e.: 4.5 ± 1.5; P < 0.0001). A synergistic effect of nonane mixed with untreated soil was also found in Cx. quinquefasciatus (median value ± s.e.: 41.0 ± 2.1; P < 0.0001) compared to either nonane (median value ± s.e. 19.0 ± 1.3; P < 0.0001) or untreated soil alone (median value ± s.e.: 17.0 ± 2.0; P < 0.0001). The oviposition activity index for An. gambiae was 0.56 (P < 0.001) and for Cx. quinquefasciatus 0.59 (P < 0.0001).

CONCLUSIONS

The larval pheromone nonane and emanations from breeding-site soil both induced oviposition in wild An. gambiae s.l. and Cx. quinquefasciatus, with a synergistic effect when both stimuli were present simultaneously. This is the first study in which nonane is shown to cause oviposition under natural conditions, suggesting that this compound can potentially be exploited for the management of mosquito vectors.

Exploiting the chemical ecology of mosquito oviposition behavior in mosquito surveillance and control: a review

Vector control is an important component of the interventions aimed at mosquito-borne disease control. Current and future mosquito control strategies are likely to rely largely on the understanding of the behavior of the vector, by exploiting mosquito biology and behavior, while using cost-effective, carefully timed larvicidal and high-impact, low-volume adulticidal applications. Here we review the knowledge on the ecology of mosquito oviposition behavior with emphasis on the potential role of infochemicals in surveillance and control of mosquito-borne diseases. A search of PubMed, Embase, Web of Science, Global Health Archive, and Google Scholar databases was conducted using the keywords mosquito, infochemical, pheromone, kairomone, allomone, synomone, apneumone, attractant, host-seeking, and oviposition. Articles in English from 1974 to 2019 were reviewed to gain comprehensive understanding of current knowledge on infochemicals in mosquito resource-searching behavior. Oviposition of many mosquito species is mediated by infochemicals that comprise pheromones, kairomones, synomones, allomones, and apneumones. The novel putative infochemicals that mediate oviposition in the mosquito subfamilies Anophelinae and Culicinae were identified. The role of infochemicals in surveillance and control of these and other mosquito tribes is discussed with respect to origin of the chemical cues and how these affect gravid mosquitoes. Oviposition attractants and deterrents can potentially be used for manipulation of mosquito behavior by making protected resources unsuitable for mosquitoes (push) while luring them towards attractive sources (pull). In this review, strategies of targeting breeding sites with environmentally friendly larvicides with the aim to develop appropriate trap-and-kill techniques are discussed.

An annotated dataset of bioacoustic sensing and features of mosquitoes

As vectors of malaria, dengue, zika, and yellow fever, mosquitoes are considered one of the more severe worldwide health hazards. Widespread surveillance of mosquitoes is essential for understanding their complex ecology and behaviour, and also for predicting and formulating effective control strategies against mosquito-borne diseases. One technique involves using bioacoustics to automatically identify different species from their wing-beat sounds during flight. In this dataset, we collect sounds of three species of mosquitoes: Aedes Aegypti, Culex Quinquefasciatus & Pipiens, and Culiseta. These species were collected and reproduced in the laboratory of the Natural History Museum of Funchal, in Portugal, by entomologists trained to recognize and classify mosquitoes. For collecting the samples, we used a microcontroller and a mobile phone. The dataset presents audio samples collected with different sampling rates, where 34 audio features characterize each sound file, making it is possible to observe how mosquito populations vary heterogeneously. This dataset provides the basis for feature extraction and classification of flapping-wing flight sounds that could be used to identify different species.

Measurement(s)	Sound • audio feature
Technology Type(s)	bioacoustic sensing • audio board • Microphone Device • sensor • mobile phone
Factor Type(s)	species of mosquito • sampling rate
Sample Characteristic - Organism	Aedes aegypti • Culex pipiens x Culex quinquefasciatus • Culiseta
Sample Characteristic - Location	Madeira

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.13034597

Susceptibility of mosquito vectors of the city of Praia, Cabo Verde, to Temephos and Bacillus thuringiensis var israelensis

Many vector-borne diseases circulate in the Republic of Cabo Verde. These include malaria during the colonization of the archipelago by the Portuguese explorers and several arboviruses such as yellow fever (now eradicated), dengue and zika.

To control these vector-borne diseases, an integrated vector control program was implemented. The main targeted mosquito vectors are Aedes aegypti and Anopheles arabiensis, and in a lesser extent the potential arbovirus vector Culex pipiens s.l. The main control strategy is focused on mosquito aquatic stages using diesel oil and Temephos. This latter has been applied in Cabo Verde since 1979. Its continuous use was followed by the emergence of resistance in mosquito populations.

We investigated the current susceptibility to Temephos of the three potential mosquito vectors of Cabo Verde through bioassays tests. Our results showed various degrees of susceptibility with 24h post-exposure mortality rates ranging from 43.1% to 90.9% using WHO diagnostic doses. A full susceptibility was however observed with Bacillus thurigiensis var israelensis with mortality rates from 99.6% to 100%.

An odorant receptor from Anopheles sinensis in China is sensitive to oviposition attractants

Background

Anopheles sinensis is an important vector for the spread of malaria in China. Olfactory-related behaviours, particularly oviposition site seeking, offer opportunities for disrupting the disease-transmission process.

Results

This is the first report of the identification and characterization of AsinOrco and AsinOR10 in An. sinensis. AsinOrco and AsinOR10 share 97.49% and 90.37% amino acid sequence identity, respectively, with related sequences in Anopheles gambiae. A functional analysis demonstrated that AsinOrco- and AsinOR10-coexpressing HEK293 cells were highly sensitive to 3-methylindole, but showed no significant differences in response to other test odorants when compared to DMSO.

Conclusions

AsinOrco was characterized as a new member of the Orco ortholog subfamily. AsinOR10, which appears to be a member of the OR2-10 subfamily, is directly involved in identification of oviposition sites. This finding will help to elucidate the molecular mechanisms underlying olfactory signaling in An. sinensis and provide many more molecular targets for eco-friendly pest control.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2501-4) contains supplementary material, which is available to authorized users.

Mosquito Oviposition Behavior and Vector Control

The burden of gene transfer from one mosquito generation to the next falls on the female and her eggs. The selection of an oviposition site that guarantees egg and larval survival is a critical step in the reproductive process. The dangers associated with ephemeral aquatic habitats, lengthy droughts, freezing winters, and the absence of larval nutrition makes careful oviposition site selection by a female mosquito extremely important. Mosquito species exhibit a remarkable diversity of oviposition behaviors that ensure eggs are deposited into microenvironments conducive for successful larval development and the emergence of the next mosquito generation. An understanding of mosquito oviposition behavior is necessary for the development of surveillance and control opportunities directed against specific disease vectors. For example, Aedes aegypti Linnaeus is the vector of viruses causing important human diseases including yellow fever, dengue, chikungunya, and Zika. The preference of this species to oviposit in natural and artificial containers has facilitated the development of Ae. aegypti-specific surveillance and toxic oviposition traps designed to detect and control this important vector species in and around disease foci. A better understanding of the wide diversity of mosquito oviposition behavior will allow the development of new and innovative surveillance and control devices directed against other important mosquito vectors of human and animal disease.

Mosquito Surveillance and the First Record of the Invasive Mosquito Species Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae) in Southern Iran

BACKGROUND

Epidemics of mosquito-borne viral infections such as dengue, chikungunya, West Nile and Rift Valley fevers in neighbouring countries and risk of introduction of exotic vectors into Iran have placed this country at a significant risk for these mosquito-borne diseases.

METHODS

After the first dengue case reported in Iran in 2008, active entomological surveillance of Aedes albopictus (Skuse) and Ae. aegypti (Linnaeus) were conducted in May/Jun, Sep, and Oct/Nov, 2008-2014. Based on occurrence of dengue cases and the presence of potential entry sides including ports and boarder gates, 121 sites in eight provinces were monitored for mosquito vectors. Larval collections were carried out using droppers or dippers and adult collections with CDC light traps, human landing catches, aspirator and Pyrethrum spray space catches.

RESULTS

A total of 8,186 larvae and 3,734 adult mosquitoes were collected belonging to 23 Culicinae species, including 13 of the genus Culex, 1 Culiseta, 1 Uranotaenia, and 8 of the genus Aedes. Five Aedes albopictus larvae were identified from the Sistan & Baluchestan province bordering Pakistan in 2009. In 2013, seven Ae. albopictus adult mosquitoes were also collected in a coastal locality near the city of Chabahar in the same province.

CONCLUSION

The detection of larvae and adults of this species in different parts of this province reveal its probable establishment in southeast Iran, which has implications for public health and requires active entomological surveillance as well as the implementation of vector control to prevent the further spread of this critical vector.

Bioinsecticide and leaf litter combination increases oviposition and reduces adult recruitment to create an effective ovitrap for Culex mosquitoes

Mosquito egg traps, aquatic habitats baited with oviposition attractant and insecticide, are important tools for surveillance and control efforts in integrated vector management programs. The bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti) is increasingly used as an environmentally friendly alternative to chemical insecticides and the combination of Bti with a simple oviposition attractant like leaf litter to create an effective egg trap seems appealing. However, previous research suggests that Bti may itself alter oviposition, and that leaf litter may dramatically reduce Bti toxicity. Here we present results from field experiment designed to link the effects of litter and Bti on mosquito oviposition habitat selection and post-colonization survival to production of adult mosquitoes. Tripling litter increased Culex spp. oviposition nearly nine-fold, while Bti had no effect on oviposition. Neither factor altered egg survival, thus larval abundance reflected the effects of litter on oviposition. Both Bti and litter reduced larval survival by ∼60%. We found no evidence that increased litter reduced Bti toxicity. Adult production was dependent upon both litter and Bti. In the absence of Bti, effects of litter on oviposition translated into three-fold more adults. However, in the presence of Bti, initial increases in oviposition were erased by the combined negative effects of Bti and litter on post-colonization survival. Thus, our study provides field evidence that combined litter and Bti application creates an effective ovitrap. This combined treatment had the highest oviposition and the lowest survival, and thus removed the greatest number of mosquitoes from the landscape.

Crystal and solution structures of an odorant-binding protein from the southern house mosquito complexed with an oviposition pheromone

Culex mosquitoes introduce the pathogens responsible for filariasis, West Nile virus, St. Louis encephalitis, and other diseases into humans. Currently, traps baited with oviposition semiochemicals play an important role in detection efforts and could provide an environmentally friendly approach to controlling their populations. The odorant binding proteins (OBPs) in the female's antenna play a crucial, if yet imperfectly understood, role in sensing oviposition cues. Here, we report the X-ray crystallography and NMR 3D structures of OBP1 for Culex quinquefasciatus (CquiOBP1) bound to an oviposition pheromone (5R,6S)-6-acetoxy-5-hexadecanolide (MOP). In both studies, CquiOBP1 had the same overall six-helix structure seen in other insect OBPs, but a detailed analysis revealed an important previously undescribed feature. There are two models for OBP-mediated signal transduction: (i) direct release of the pheromone from an internal binding pocket in a pH-dependent fashion and (ii) detection of a pheromone-induced conformational change in the OBP·pheromone complex. Although CquiOBP1 binds MOP in a pH-dependent fashion, it lacks the C terminus required for the pH-dependent release model. This study shows that CquiOBP binds MOP in an unprecedented fashion using both a small central cavity for the lactone head group and a long hydrophobic channel for its tail.

Odorant receptor from the southern house mosquito narrowly tuned to the oviposition attractant skatole

Oviposition attractants are environmental cues that allow Culex gravid female mosquitoes to locate suitable sites for egg-laying and, therefore, may be exploited for environmentally friendly strategies for controlling mosquito populations. Naturally occurring skatole has been identified as an oviposition attractant for the Southern House mosquito, Culex quinquefasciatus. Previously, we identified in Cx. quinquefasciatus female antennae an olfactory receptor neuron (ORN) highly sensitive to skatole and an odorant-binding protein involved in the detection of this semiochemical. Here, we describe the characterization of an odorant receptor (OR), CquiOR10, which is narrowly tuned to skatole when expressed in the Xenopus oocyte system. Odorant-induced response profiles generated by heterologously expressed CquiOR10 suggest that this OR is expressed in the mosquito ORN sensitive to skatole. However, geranylacetone, which stimulates the antennal ORN, was not detected by CquiOR10-expressing oocytes, thus raising interesting questions about reception of oviposition attractants in mosquitoes.