Quantitative Evaluation of the Behavioral Response to Attractant and Repellent Compounds in Anopheles pseudopunctipennis and Aedes aegypti (Diptera: Culicidae) Larvae.

The mosquito Anopheles pseudopunctipennis (Theobald) is the principal vector for malaria in Latin-America. Aedes aegypti (L.) (Diptera: Culicidae) is the key vector of four important arboviral diseases: dengue, yellow fever, Zika, and chikungunya. Controlling larval stages to reduce the production of new adult mosquitoes is part of the integrated vector management strategies. However, there are few studies about the olfactory behavior on immature stages of mosquitoes, especially in An. pseudopunctipennis. In this work, we have evaluated the behavior of An. pseudopunctipennis and Ae. aegypti larvae in response to attractant or repellent stimuli through a video-tracking analysis. We used the software EthoVision to obtain behavioral variables related to the swimming activity, such as distance, speed, and mobility status. The response to the repellents stimulus results in an increase of the swimming activity and the absolute angular velocity in both species. Otherwise, the responses to the possible attractants stimulus results in a decrease of the activity of the larvae only for Ae. aegypti. The effects of these compounds were weaker in Anopheles; probably as a consequence of their adaptations to different aquatic ecosystems. The study of the larval olfactory response could contribute to the development of new control tools based on 'push-pull' strategies by 'pushing' mosquitoes away from certain places using repellents, and 'pulling' them towards other places like traps baited with attractive cues.

Volatile compounds secreted by Brindley's glands of adult Triatoma infestans: identification and biological activity of previously unidentified compounds.

Volatile emissions of adult male Triatoma infestans were collected on non-polar SPME fibers and analyzed by gas chromatography linked to a mass spectrometer. A complex mixture of 16 short-chain esters and acids were identified. The composition of short-chain aliphatic acids (ethanoic to nonanoic acids) was similar to previously reported results. The most abundant aliphatic acid was 2-methylpropanoic acid, constituting 18% of the total volatile content. Also abundant were the esters 2- and 3-methylbutyl 2-methylpropanoate, which constituted 30% and 22%, respectively, of the total volatile content. A similar pattern of compounds was observed in the volatiles secreted by dissected male Brindley's glands; however, in this case, 2- and 3-methylbutan-1-ol were detected which were not found in live insect volatile emissions. Large variability in volatile composition was also observed among the glands excised from different insects. Electroantennographic (EAG) evaluation of the components of Brindley's gland showed significant responses for 2- and 3-methylbutyl 2-methylpropanoate compared to controls. The mixture of volatiles secreted by excised Brindley's glands and the isolated 2- and 3-methylbutyl 2-methylpropanoate had repellent effects on both male and female T. infestans, possibly associated with a defensive strategy.

Behavioural response of Triatoma infestans (Klug) (Hemiptera: Reduviidae) to quinazolines.

The behavioural responses of the haematophagous bug Triatoma infestans towards some previously identified components of its faeces: 4-methylquinazoline, 2,4- dimethylquinazoline and their mixtures were evaluated using a video tracking system. Fifth instar nymphs and females but not males were significantly attracted to polyethylene glycol formulations of 4-methyl + 2,4-dimethylquinazoline (50 microg each). Fifth instar nymphs were also attracted to 4-methylquinazoline alone (50 microg) but females were only attracted by the mixture of both methyl quinazolines (50 microg each). Syntheses of both methyl quinazolines were carried out starting from 2-aminoacetophenone by modifying the conditions of reported procedures.

Investigation of long-range female sex pheromone of the European tarnished plant bug, Lygus rugulipennis: chemical, electrophysiological, and field studies.

The European tarnished plant bug, Lygus rugulipennis, is an important pest of agricultural and horticultural crops throughout Europe. Adult male L. rugulipennis were previously shown to be attracted to traps baited with live virgin females, which suggests the females produce a sex pheromone. Volatiles produced by virgin female L. rugulipennis were shown to contain three components, hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal which elicited electroantennographic (EAG) responses from males in analyses by linked gas chromatography-electroantennography (GC-EAG). They were produced in 1.5:1:0.08 ratio, respectively, by single females. Collections from 1, 2, or 4 virgin females showed the proportions of hexyl butyrate and (E)-4-oxo-2-hexenal to increase relative to that of (E)-2-hexenyl butyrate with increasing number of females. Although these compounds were found in body extracts of both male and female L. rugulipennis, they were not detected in volatiles released by virgin males. EAG dose-response studies showed that both males and females responded to these chemicals with minimal differences in sensitivity between the sexes or to the three components, except that males were more responsive than females to (E)-4-oxo-2-hexenal at the two highest doses tested. Release rates of the compounds from rubber septa, polyethylene vials, and polyethylene sachets were measured under laboratory conditions. Four field tests were carried out using sticky traps baited with all possible binary and tertiary combinations of the three chemicals using different combinations of dispensing systems. Catches of male L. rugulipennis in baited traps were similar to those in unbaited traps. Significantly fewer females were caught on traps baited with blends containing hexyl butyrate than on traps without hexyl butyrate or unbaited traps in one test and overall. The roles of the three compounds and possible reasons for their failure to attract males are discussed.

Residualidad de un formulado sólido del insecticida microbiano Bti (H-14) en el control de larvas de Aedes aegypti (Diptera: Culicidae) / Residuality of a microbial insecticide solid formulated Bti (H-14) in the

El Bacillus thuringiensis var. israelensis (Bti ó Bti H-14) produce una toxina proteica, la cual constituye una herramienta de gran utilidad para el control de larvas de Aedes aegypti. Una suspensión líquida de la toxina y las esporas (Bti) ha sido utilizada en campañas nacionales de control del mosquito vector del Dengue en Argentina, pero la falta de efecto residual constituye elmayor inconveniente para su aplicación. En la búsqueda de nuevas estrategias para el control de vectores de enfermedades, este trabajo presenta algunos resultados sobre una nueva formulación de liberación controlada de Bti, denominada ôMosquito Dunks®õ. Se utilizaron larvas de Ae. aegypti del III estadio tardío ó IV temprano (cepa susceptible CIPEIN) que en ensayos de laboratorio demostraron una actividad residual a dosis de uso recomendadas por el fabricante (14,4 mg/cm2) de al menos 180 días con mortalidad total luego de 48 horas de exposición. Los resultados que se presentan en este trabajo sugieren que la nueva formulación sólida de liberación lenta de Bti, debido a su residualidad representa una buena alternativa para el reemplazo del Temefos en el control de larvas de Aedes aegypti, especialmente en aquellos casos donde se detecte resistencia al larvicida organofosforado.

The entomopathogenous agent Bacillus thuringensis var. israelensis (Bti or Bti H-14), produces a proteic toxin that is a promissory tool to use in chemical control of larvae of Aedes aegypti. Bti (H-14) as a liquid suspension, has been used in national campaigns against Ae. aegypti , vector of Dengue disease, but its lack of residual effect is a major inconvenient. In the search of new strategies in vector control, this paper presents some results of an alternative slow release formulation of Bti (H-14), the ôMosquito Dunksõ . III instar or young IV instar larvae of a susceptible strain of Aedes aegypti (CIPEIN strain) was used in laboratory assays. The ôMosquito Dunksõ at recommended use dosis (14,4 mg / 100 cm2 surface) were assayed for residual activity. 100% mortality was found for at least 180 days (6 month) with 48 hs larvae exposition. The results presented in this work suggests that this new solid slow release formulation of Bti with more residual activity could be a good alternative for Temephos for Aedes aegypti larvae control, specially for those cases in which resistance to the organophosphorus compound is reported.

Effect of GSH depletion mediated by l-BSO on the insecticidal activity of DDT and fenitrothion in Triatoma infestans (Hemiptera).

l-BSO injected at a sublethal dose in nymph V of Triatoma infestans produces a transient GSH depletion in the abdomen. A depletion of the total content of GSH was observed in nymph II fed with a sublethal concentration of l-BSO. Either ingestion or injection pretreatments of T. infestans nymph V with sublethal concentrations of l-BSO produced a slight synergism on the toxicity of fenitrothion. Feeding administration of a sublethal concentration of l-BSO to nymphs II of T. infestans resulted in a weak potentiation of the acute toxicity of DDT.