It is known that human individuals show different levels of attractiveness to mosquitoes. In this study, we investigated the chemical basis for low attractiveness. We recorded behaviors of Aedes aegypti toward the hands of human volunteers and toward the volatile chemicals produced by their bodies. Some individuals, and their corresponding volatiles, elicited low upwind flight, relative attraction, and probing activity. Analyzing the components by gas chromatography coupled to electrophysiological recordings from the antennae of Aedes aegypti, enabled the location of 33 physiologically relevant compounds. The results indicated that higher levels of specific compounds may be responsible for decreased "attractiveness." In behavioral experiments, five of the compounds caused a significant reduction in upwind flight of Aedes aegypti to attractive human hands. Thus, unattractiveness of individuals may result from a repellent, or attractant "masking," mechanism.

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Azadiractina do Nim, Azadirachta indica: sua Ação Contra Insetos RESUMO -A árvore do nim há muito tempo é reconhecida por suas propriedades singulares de ação contra insetos e benefício à saúde humana. É plantada na maior parte das áreas tropicais e subtropicais do mundo para sombra, reflorestamento e produção de matéria prima para inseticidas naturais e medicamentos. A azadiractina, complexo tetranortriterpenóide limonóide das sementes é o principal composto responsável pelos efeitos tóxicos aos insetos. Seis conferências internacionais sobre nim e vasta literatura científica relatam esses aspectos. Este artigo revê as propriedades da azadiractina no comportamento e na fisiologia de insetos, incluindo os efeitos na reprodução, redução da alimentação tanto direto quanto a chamada "secundária", redução do crescimento, aumento da mortalidade e ocorrência de ecdises anormais e tardias. Os efeitos fisiológicos são aqui categorizados de duas maneiras: efeitos diretos sobre as células e os tecidos e efeitos indiretos exercidos via o sistema endócrino. O artigo também descreve o trabalho feito até o momento visando identificar o modo de açao da azadiractina em nível celular e seus efeitos diferentes entre filos animais e sobre organismos não nocivos, o que indica seu sucesso potencial como inseticida seguro. PALAVRAS-CHAVE: Insecta, inseticida botânico, fisiologia de insetos.ABSTRACT -The neem tree has long been recognized for its unique properties both against insects and in improving human health. It is grown in most tropical and sub-tropical areas of the world for shade, reforestation and for the production of row material for natural insecticides and medicines. Azadirachtin, a complex tetranortriterpenoid limonoid from the neem seeds, is the main component responsible for the toxic effects in insects. Six international conferences on neem and a vast scientific literature report both the antifeedant and physiological effects of neem. This article reviews the behavioral and physiological properties of azadirachtin, including effects on insect reproduction, direct and "secondary" antifeedancy, and the physiological effects measured as growth reduction, increased mortality and abnormal and delayed moults. These effects are here categorized in two ways: direct effects on cells and tissues and indirect effects exerted via the endocrine system. It also describes the work carried out to date to identify the mode of action of azadirachtin at the cellular level. The differential effects between animal phyla and over non-target organisms are discussed and point to its potential success as a safe insecticide.

The role and identity of host and non-host chemical cues (semiochemicals) in host location and non-host avoidance for copepodid larvae of sea lice, Lepeophtheirus salmonis, was investigated using Y-tube behavioural bioassays, solid-phase extraction (SPE), and coupled gas chromatography – mass spectrometry (GC–MS). Using artificial seawater conditioned with the preferred salmonid host, Salmo salar, L. salmonis displayed high activation and directional responses in Y-tube assays to salmon-conditioned water (SCW), to an extract of SCW prepared by SPE, and to a vacuum distillate of the SPE extract. Similar responses were observed to two chemicals identified from SCW by coupled GC–MS: isophorone and 6-methyl-5-hepten-2-one. Dose-response studies with isophorone showed that copepodid responses across the range tested were maximised at 0.01 and 0.1 mg·mL–1. A mixture of isophorone and 6-methyl-5-hepten-2-one also induced high activation and directional responses. Semiochemicals were also isolated from the non-host fish, turbot (Scophthalmus maximus (Rafinesque)), by SPE and analysed by GC–MS. Two non-host-specific chemicals were identified as 2-aminoacetophenone and 4-methylquinazoline. When SCW was mixed with either of the non-host chemicals, activation and directional responses to SCW were eliminated in the Y tube.

The biting midge Culicoides imicola Kieffer (Diptera: Ceratopogonidae) is the most important Old World vector of African horse sickness (AHS) and bluetongue (BT). Recent increases of BT incidence in the Mediterranean basin are attributed to its increased abundance and distribution. The phylogenetic status and genetic structure of C. imicola in this region are unknown, despite the importance of these aspects for BT epidemiology in the North American BT vector. In this study, analyses of partial mitochondrial cytochrome oxidase subunit I gene (COI) sequences were used to infer phylogenetic relationships among 50 C. imicola from Portugal, Rhodes, Israel, and South Africa and four other species of the Imicola Complex from southern Africa, and to estimate levels of matrilineal subdivision in C. imicola between Portugal and Israel. Eleven haplotypes were detected in C. imicola, and these formed one well-supported clade in maximum likelihood and Bayesian trees implying that the C. imicola samples comprise one phylogenetic species. Molecular variance was distributed mainly between Portugal and Israel, with no haplotypes shared between these countries, suggesting that female-mediated gene flow at this scale has been either limited or non-existent. Our results provide phylogenetic evidence that C. imicola in the study areas are potentially competent AHS and BT vectors. The geographical structure of the C. imicola COI haplotypes was concordant with that of BT virus serotypes in recent BT outbreaks in the Mediterranean basin, suggesting that population subdivision in its vector can impose spatial constraints on BT virus transmission.

Culicoides biting midges (Diptera: Ceratopogonidae) vector a wide variety of internationally important arboviral pathogens of livestock and represent a widespread biting nuisance. This study investigated the influence of landscape, host and remotely-sensed climate factors on local abundance of livestock-associated species in Scotland, within a hierarchical generalized linear model framework. The Culicoides obsoletus group and the Culicoides pulicaris group accounted for 56% and 41%, respectively, of adult females trapped. Culicoides impunctatus Goetghebuer and C. pulicaris s.s. Linnaeus were the most abundant and widespread species in the C. pulicaris group (accounting for 29% and 10%, respectively, of females trapped). Abundance models performed well for C. impunctatus, Culicoides deltus Edwards and Culicoides punctatus Meigen (adjusted R(2) : 0.59-0.70), but not for C. pulicaris s.s. (adjusted R(2) : 0.36) and the C. obsoletus group (adjusted R(2) : 0.08). Local-scale abundance patterns were best explained by models combining host, landscape and climate factors. The abundance of C. impunctatus was negatively associated with cattle density, but positively associated with pasture cover, consistent with this species' preference in the larval stage for lightly grazed, wet rush pasture. Predicted abundances of this species varied widely among farms even over short distances (less than a few km). Modelling approaches that may facilitate the more accurate prediction of local abundance patterns for a wider range of Culicoides species are discussed.

BackgroundIndividual human subjects are differentially attractive to mosquitoes and other biting insects. Previous investigations have demonstrated that this can be attributed partly to enhanced production of natural repellent chemicals by those individuals that attract few mosquitoes in the laboratory. The most important compounds in this respect include three aldehydes, octanal, nonanal and decanal, and two ketones, 6-methyl-5-hepten-2-one and geranylacetone [(E)-6,10-dimethylundeca-5,9-dien-2-one]. In olfactometer trials, these compounds interfered with attraction of mosquitoes to a host and consequently show promise as novel mosquito repellents.MethodsTo test whether these chemicals could provide protection against mosquitoes, laboratory repellency trials were carried out to test the chemicals individually at different concentrations and in different mixtures and ratios with three major disease vectors: Anopheles gambiae, Culex quinquefasciatus and Aedes aegypti.ResultsUp to 100% repellency was achieved depending on the type of repellent compound tested, the concentration and the relative composition of the mixture. The greatest effect was observed by mixing together two compounds, 6-methyl-5-hepten-2-one and geranylacetone in a 1:1 ratio. This mixture exceeded the repellency of DEET when presented at low concentrations. The repellent effect of this mixture was maintained over several hours. Altering the ratio of these compounds significantly affected the behavioural response of the mosquitoes, providing evidence for the ability of mosquitoes to detect and respond to specific mixtures and ratios of natural repellent compounds that are associated with host location.ConclusionThe optimum mixture of 6-methyl-5-hepten-2-one and geranylacetone was a 1:1 ratio and this provided the most effective protection against all species of mosquito tested. With further improvements in formulation, selected blends of these compounds have the potential to be exploited and developed as human-derived novel repellents for personal protection.