Blood feeding insects are entwined with the history of mankind and our livestock, with the irritation of arthropod bites bringing a range of vector borne diseases that have devastated human populations. The three documented pandemics of Bubonic plague are more than matched by the constant losses to malaria that have only in recent history been brought under one million per year. Military campaigns throughout history have lost more troops to disease, often vector-borne, than to fighting and malaria and yellow fever devastated the first workers on the Panama Canal and a plethora of other endeavours. Whilst DDT brought some relief, first to the troops of World War II and then to the wider populations, the use of insecticides on a wide scale came at an enormous ecological cost. The more focused use of insecticides in indoor spraying and bed-net campaigns further contributed to the decline of malaria incidence but appear to have begun to reach the limit of what their efficacy can achieve. In these times we need to expand our toolbox, and we need to do so through a better understanding of the ecology and behaviour of vectors of disease. We need to expand our knowledge base of a wider range of vectors because to extrapolate from studies of one species in one situation rarely gives information of sufficient quality for our needs. When it comes to the specific behavior that drives the transmission of disease by a vector then the devil is truly in the detail.
Triatomine bugs are insect models since the initiation of insect physiological studies, and their role in transmitting human disease. Triatomines can inhabit arboreal ecotopes, as well as underground burrows, where they associate with diverse vertebrates. These nocturnal insects obtain their blood meals from hosts, which can predate on them. Therefore, obtaining a meal is a dangerous activity requiring stealth. For promoting and adjusting this behaviour, these bugs exploit diverse host cues, the main ones being carbon dioxide, infrared radiation, odours and contact cues present on host fur and skin. Besides host-related odours, triatomines use pheromones to communicate in diverse behavioural contexts. As these bugs hide in narrow shelters during daylight hours, some species can mark the entrance of these structures with their own faeces, promoting the aggregation of hidden colonies. Once inside, triatomines can also signal an active refuge by depositing nonvolatile cuticular compounds, named footprints, which promote their arrestment. Adults of these insects present two pairs of exocrine glands, the Brindley’s and metasternal glands. The compounds emitted by the former, i.e. a blend made mostly of isobutyric acid, promote alarm among other individuals. The second pair of glands can produce a mixture of ketones, dioxolanes and alcohols depending on the species involved. These extremely volatile compounds, mostly emitted by adult females, are considered sexually-related signals, communicating female willingness to mate. The blends secreted by the metasternal glands can trigger male arousal, and mediate diverse steps of male approach. The blends of females and males are indeed necessary to promote proper mating success. Perspectives on the chemical ecology of kissing bugs are discussed in relation to new methodologies and pending questions that deserve attention.
The reproduction of sand flies is dependent on the intake of vertebrate blood by females, which is used to produce eggs. The blood-feeding process involves sophisticated mechanisms of host-seeking behaviour, and may result in the transmission of Leishmania parasites, and other human and animal disease agents. A mechanistic knowledge of these processes is paramount to understand disease epidemiology, and to develop tools and strategies for monitoring and control of sand fly vectors. This chapter provides a comprehensive review of the literature on the host-seeking behaviour of phlebotomine sand flies and highlights the knowledge gaps to be addressed in future investigations. Sand fly host-seeking behaviour is triggered by intrinsic physiological mechanisms, as well as extrinsic environmental factors. Studies conducted around the world show that sand flies are attracted to carbon dioxide. Of all other volatile compounds emitted by hosts, the racemic mixture of 1-octen-3-ol elicits consistent attraction in some sand fly species under field conditions, whereas other tested host compounds elicit attraction only in laboratory experiments. Although physical cues, such as host temperature, shape and colour, are suspected to play important roles in host location, little is known about how these cues attract sand flies to particular hosts, and how they interact with chemical cues to elicit host-seeking behaviour. Despite efforts made to improve the efficiency of sand fly traps by utilising host-volatile compounds as lures, few field studies have been performed to quantify sand fly attraction to these traps. We recommend that further studies are urgently needed to identify physical cues and additional host chemicals, which attract sand flies, and determine the concentrations and distance of attraction of these cues. Knowledge from such studies will facilitate the design of traps for sand flies, and will be of great value for disease control programmes.
This chapter explores how mosquito-borne pathogens influence vector host-seeking and feeding behaviours. Even before a mosquito acquires a pathogen by feeding on an infected host, its behaviour can be influenced by indirect effects of infection on host traits, such as the olfactory cues that mediate vector attraction. Following acquisition, pathogens may also exert direct influence on relevant aspects of mosquito behaviour, including feeding frequency and persistence, patterns of activity and movement, and the perception of and response to host-derived cues. There is evidence that both direct and indirect (host-mediated) effects of pathogens on vector behaviour are frequently conducive to transmission. Moreover, similar effects reported from diverse pathosystems suggest possible convergent evolution. Given their relevance for pathogen transmission and epidemiology, such effects have important implications for human health.
Sand flies are an ancient group of Diptera estimated to contain 1000 species. Approximately 70 of these transmit pathogens (viruses, bacteria and protists), which cause human and animal diseases. The most important are the Leishmania parasites, transmitted to humans and animals, during blood feeding by female sand flies, and which cause diseases that can be fatal or disfiguring. Sand flies are known to use volatile chemicals produced by plants to locate sugar meals, host odours to locate a blood meal, and chemicals from decaying vegetation and other sources to identify oviposition sites. In a limited number of cases, male sand flies also produce volatile chemicals (sex/aggregation pheromones) that are attractive to females and other males. The presence of sex/aggregation pheromones is well documented in Lutzomyia longipalpis sensu lato, the South American vector of Leishmania infantum, in which they were first identified 40 years ago. During this time, a range of behavioural and chemical methodologies have been applied to their study in the laboratory and the field. The presence of sex/aggregation pheromones has also been suggested in a small number of other New and Old-World vectors, but the evidence is incomplete, as it is either solely chemical, i.e. without supporting behavioural evidence or behavioural evidence is available, but there is no supporting chemical evidence. Within the Lu. longipalpis s.l. species complex, the sex/aggregation pheromones provide a taxonomic guide to the members of the complex. There are four different known chemical types (five members of the complex), and one of these, the most geographically widespread, has been synthesised in bulk quantity. The synthetic pheromone, co-located with insecticide, has been shown to significantly reduce numbers of sand flies, and leishmania infection in dogs, the reservoir of human infection, and could significantly impact the number of human cases.
The exploration of the chemical ecology of oviposition behaviour in mosquitoes provides the means to describe the role of volatile organic compounds used by gravid mosquitoes to secure intrinsic fitness. Gravid mosquitoes do this by using odour-mediated selection for sites, which minimises larval mortality and maximises growth rate through decreased competition and predation, as well as providing increased access to food resources. Oviposition sites and their surrounding habitats are rich sources for odours. Identifying which of these odorants gravid mosquitoes are using as oviposition site cues, and in which combinations, has been under investigation for almost a century. With the advent of techniques, including combined chemical and electrophysiological detection, functional genomics and reverse chemical ecology, the screening of these vast natural resources has accelerated and provided the approaches necessary to unravel the mechanisms that regulate mosquito oviposition-site selection. The use of attractive and stimulating odorant blends as lures to surveille and control gravid and ovipositing mosquitoes has long been advocated, and with the recent advancements in chemical ecology, may soon become a reality.
Ticks represent significant challenges to animal and human health due to their roles as disease vectors, or through damage and nuisance due to feeding. These arthropods are present throughout a diverse array of environments. A common challenge to this group is communication within the species to maximise survival, and pheromonal communication is key for optimal survival in the diverse habitats of both soft and hard ticks. This chapter reviews courtship behaviour, and the different roles of pheromones in guiding tick courtship. The formation of grouping and assemblies of ticks, either on- or off-hosts, enhances survival and feeding, and the roles of pheromones in these activities are reviewed, with particular emphasis on assembly, as well as attraction, aggregation and attachment pheromones. Practical applications of pheromones are reviewed, including enhancement of rearing methods, development of population surveillance methods and various approaches to control strategies.
Male mosquitoes of haematophagous species are obligate host-plant feeders, but female mosquitoes also depend on sugary plant-derived food sources for building energy reserves and enhanced reproductive success. The significant differences between the two sexes in host-plant feeding behaviours are accompanied by sexual dimorphism in the structure and function of digestive organs, as well as in metabolic pathway regulation for utilisation of a sugar-rich diet in males, and sequential sugar-rich and blood meals in females. Host-plant food sources of mosquitoes include nectar from inflorescences and extrafloral nectaries, sap, fluid from seed pods and fruit, as well as excreta from insects that feed on plant sap. While mosquitoes use olfactory cues to find host plants, the taste system is engaged upon contact, and is involved in assessing the suitability of a meal for ingestion. Host-plant-derived food sources are rich in sugars, and also contain nutrients such as amino acids, vitamins and minerals, as well as phytochemicals that may influence memory and feeding preference. Taste responses to some of these nectar components have been identified in the mosquito labellum and tarsi, but in most cases only few sensilla have been evaluated with a few tastants. The field is primed for more in-depth investigations of taste coding in mosquitoes. While a lot can be inferred from studies in Drosophila, there exist gaps in our understanding of the molecular basis of taste detection in mosquitoes. In this chapter, we present an overview of our current understanding of host-plant feeding and the taste sensory functions that underlie it. Further investigation of mosquito taste, behaviour, and evolution may lead to new targets and strategies for mosquito control.
Blood feeding is pivotal for the survival and reproduction of haematophagous arthropods, and is intimately linked to the transmission of vector-borne diseases. As such, understanding the dynamics of phagostimulation may identify targets, which can be used in future vector control. The behaviour leading up to the acceptance of a blood meal relies ultimately on the sense of taste, by which disease vectors assess the quality of the meal through blood-related phagostimulatory ligands. Adenylated nucleotides, often in combination with NaCl, NaHCO3 and other blood-related factors, elicit pronounced, species-specific feeding responses in haematophagous arthropods, an effect reflected in the response of gustatory sensory neurons housed within hairlike sensilla on the mouthparts involved in blood feeding. While there has been progress made to understand the molecular mechanisms regulating the response to blood phagostimulants, there are yet many voids to fill. This chapter gives an account of the existing knowledge about the phagostimulatory dynamics leading up to and during blood-feeding activation in select disease vectors, with emphasis on the blood-related feeding stimulants/mechanisms, which potentially could be targeted for advancing alternative vector control tools.
Salts are naturally occurring minerals essential for animal life. Systemic deficient or excessive salt levels can result in adverse health effects for most animals, which can only be balanced by ingestion and/or excretion. Salts are detected by the taste system of all studied insects. This system is the ultimate and truly reliable sense that helps animals make predictions about the quality of a resource item, e.g. beneficial or harmful. As a general rule for terrestrial blood-feeding insects, low environmental salt detection triggers feeding and egg-laying, whereas high salt promotes different types of aversive behaviours. Despite the relevance of salts for life, the molecular and physiological mechanisms behind salt perception only recently began to be understood. Here, we summarise the current knowledge about salt perception in blood-feeding disease vectors. In particular, we focus on representative insects in two orders, Diptera (mosquitoes) and Hemiptera (kissing bugs), the most studied insects regarding salt sensing.