Behavioral response mediated by feces in Triatoma infestans (Hemiptera: Reduviidae: triatominae) susceptible and resistant to deltamethrin.

Chemical cues from feces promote aggregation behavior in Triatoma infestans nymphs and adults. Given the importance of T. infestans resistant to pyrethroids in several areas of Argentina and Bolivia, it would be important to know if there is an association with specific attraction and aggregation behaviors. These behaviors, to and surrounding refuges, play an important role in triatomine population dynamics, an important factor to consider and model for vector control strategies. The aim of the present study was to analyze the behavior of orientation to chemical signals emitted by feces from deltamethrin resistant (R) and susceptible (S) T. infestans. The behavioral assays were performed in a circular glass arena divided in two equal sectors. Fecal signals emitted by both S and R feces are attractants to fifth-instar nymphs of both S and R populations. Both toxicological phenotypes remained significantly longer on R feces, as compared to S feces. This is the first evidence in a triatomine, for the association of an aggregation behavior and insecticide resistance and may be the result of pleiotropic effects surrounding resistance genes.

History of insecticide resistance of Triatominae vectors.

In the last 15 years, different types of Triatominae resistance to different insecticides have been reported; thus, resistance may be more widespread than known, requiring better characterization and delimitation, which was the aim of this review. This review was structured on a literature search of all articles from 1970 to 2015 in the PubMed database that contained the keywords Insecticide resistance and Triatominae . Out of 295 articles screened by title, 33 texts were selected for detailed analysis. Insecticide resistance of Triatomines is a complex phenomenon that has been primarily reported in Argentina and Bolivia, and is caused by different factors (associated or isolated). Insecticide resistance of Triatominae is a characteristic inherited in an autosomal and semi-dominant manner, and is polygenic, being present in both domestic and sylvatic populations. The toxicological profile observed in eggs cannot be transposed to different stages of evolution. Different toxicological profiles exist at macro- and microgeographical levels. The insecticide phenotype has both reproductive and developmental costs. Different physiological mechanisms are involved in resistance. Studies of Triatomine resistance to insecticides highlight three deficiencies in interpreting the obtained results: I) the vast diversity of methodologies, despite the existence of a single guiding protocol; II) the lack of information on the actual impact of resistance ratios in the field; and III) the concept of the susceptibility reference lineage. Research on the biological and behavioral characteristics of each Triatominae species that has evolved resistance is required in relation to the environmental conditions of each region.

History of insecticide resistance of Triatominae vectors

In the last 15 years, different types of Triatominae resistance to different insecticides have been reported; thus, resistance may be more widespread than known, requiring better characterization and delimitation, which was the aim of this review. This review was structured on a literature search of all articles from 1970 to 2015 in the PubMed database that contained the keywords Insecticide resistance and Triatominae . Out of 295 articles screened by title, 33 texts were selected for detailed analysis. Insecticide resistance of Triatomines is a complex phenomenon that has been primarily reported in Argentina and Bolivia, and is caused by different factors (associated or isolated). Insecticide resistance of Triatominae is a characteristic inherited in an autosomal and semi-dominant manner, and is polygenic, being present in both domestic and sylvatic populations. The toxicological profile observed in eggs cannot be transposed to different stages of evolution. Different toxicological profiles exist at macro- and microgeographical levels. The insecticide phenotype has both reproductive and developmental costs. Different physiological mechanisms are involved in resistance. Studies of Triatomine resistance to insecticides highlight three deficiencies in interpreting the obtained results: I) the vast diversity of methodologies, despite the existence of a single guiding protocol; II) the lack of information on the actual impact of resistance ratios in the field; and III) the concept of the susceptibility reference lineage. Research on the biological and behavioral characteristics of each Triatominae species that has evolved resistance is required in relation to the environmental conditions of each region.

After five years of chemical control: colonies of the triatomine Eratyrus mucronatus are still present in Bolivia.

Chagas disease, which is caused by the parasite Trypanosoma cruzi, is transmitted to humans by blood-sucking bugs (Triatominae). Eratyrus mucronatus is a well-dispersed triatomine species, found sometimes in dwellings. In the Apolo region of Bolivia, people continue to complain of bites by this bug despite five years of chemical control. For the first time, the domiciliation process of E. mucronatus was evaluated in a zone treated by insecticide, and it was compared with a previous situation 14 years ago. Both an entomological and a serological study were carried out: 152 dwellings were visited and 491 blood samples were analyzed with Stat-Pack and ELISA tests. In 34 dwellings (23% of the total visited dwellings), 160 triatomines of all stages were collected belonging to two species, E. mucronatus (98% of the capture) and Panstrongylus geniculatus. A domiciliation of E. mucronatus is demonstrated, particularly in the peridomicile. Bugs were captured more frequently in bedrooms in the intradomicile, and in curahuas (boundary walls in rammed mud) in the peridomicile. A P. geniculatus adult was found infected with T. cruzi. No evidence of a local vectorial transmission was found. In particular, the limited effect of the insecticide on the presence of E. mucronatus and the role of the curahuas as a source of intrusion/domiciliation process are discussed.

Decrease in DEET repellency caused by nitric oxide in Rhodnius prolixus.

N,N-diethyl-3-methylbenzamide (DEET) is widely used as an insect repellent; however, little is known about its mode of action. On the other hand, nitric oxide (NO) participates in the olfaction transduction pathway of insects. In this work, nitroso-acetyl-cysteine (SNAC), a nitric oxide donor, or dibutyril-cyclic-GMP (db-cGMP), the cyclic nucleotide analog, were applied on fifth instar nymphs of Rhodnius prolixus before exposing them to DEET, to obtain information about the possible role of NO/cGMP system in the olfaction process. In the first place, we exposed the nymphs to several DEET concentrations (70, 700, 1,750, and 3,500 microg/cm2). All these concentrations produced a repellent effect. A decrease in repellency during the course of the experiment was observed when the nymphs were exposed to high concentrations of DEET (700 and 1,750 microg/cm2), suggesting an adaptation phenomenon. The pre-treatment of the insects with 15 microg /insect of SNAC or 2 microg/insect of db-cGMP produced a reduction of the repellency. An increase in locomotor activity was observed in insects exposed to 350 or 700 microg/cm2 DEET. Although exposure to 70 microg/cm2 DEET produced a high repellency response, it did not modify the insects' locomotor activity. Insects treated with two doses of SNAC before being exposed to 350 microg/cm2 of DEET showed no differences in locomotor activity compared to controls.

[Triatomine: ovicidal action of some pyretroids]. / Triatomíneos: ação ovicida de alguns piretróides.

The insecticidal action on eggs of triatomine have been little considered in the control activitys of Chagas' disease. With objective [corrected] of to compare the potential of three synthetic pyrethroids (deltamethrin,alphacypermethrin and lambdacyhalothrin) on eggs, the authors realized laboratory tests. The pyretroid lambdacialotrin is more efficient. The following species were used in this experiment: Panstrongylus megistus and Triatoma sordida. The specie Triatoma sordida is more susceptible with the pyrethroids utilized.

Chagas disease prevention through improved housing using an ecosystem approach to health.

This Chagas disease prevention project via housing improvement aims to determine the efficiency of different interventions in vector control. The following study describes the target communities, disease magnitude, and housing improvements. Transmission levels are analysed from an ecological and socioeconomic perspective. Special interest was focused on the peridomicile as the origin of domiciliary reinfestation. In the original project, three intervention programs were proposed, one for each of the three communities: (a) an insecticide spraying program; (b) a housing improvement program; and (c) a combined program of spraying and housing improvement. The three communities currently have different risks of exposure to triatominae reinfestation as a consequence of the type of intervention carried out. A new multidisciplinary approach which integrates participatory, community-based research and socioeconomic dimensions will allow to determine the efficiency of models for territorial ordering, community education, and environmental interventions in Chagas disease control.

[The use of insecticide fumigant canister to protect an insectarium and its residual effect against triatomine bugs, in laboratory conditions]. / Emprego de pote fumígeno para proteção de insetário e sua ação residual contra triatomíneos, em condições de laboratório.

An insecticide fumigant canister based on synthetic pyrethroids and dichlorvos was employed against cockroaches and ants which were invading an insectarium used for rearing triatominae. After removal of the Triatominae, the canister was activated and found to kill all the invading insects within 48 hours. Possible residual action against triatomines was then monitored by a 24-hour exposure of eggs, nymphs and adults of Triatoma infestans, Panstrongylus megistus and Rhodnius neglectus in the treated insectarium. No ovicidal action was observed but some mortality of adults and nymphs of the three species was observed up to 72 hours after the fumigation.

Excito-repellency effect of deltamethrin on triatomines under laboratory conditions.

This work demonstrates that deltamethrin in low doses produces an excito-repellency effect on triatomines, as already observed for mosquitoes. A wooden box covered with a cloth impregnated with deltamethrin at doses of 2.5 and 5mg ai/m2 was utilized for the experiment. The triatomine species studied were Triatoma infestans, Panstrongylus megistus, Rhodnius neglectus and Triatoma sordida. Adults were released in one of the sides of the box and their position was noted in subsequent periods. The observations were realized on the day the cloth was impregnated and subsequently repeated at 30 and 60 days for T. sordida; on day 120, the remaining species were included. Insect mortality and attempts at flight from the box were also observed. Excito-repellency was evident for all species and doses up to day 120. The only species that attempted to fly was P. megistus. The excito-repellency effect may be considered as an additional advantage to the insecticide power, as it should be able to prevent the installation of new colonies by females that fly into the homes, and at the moment of the spraying, it should promote the flushing out of triatomines from the wall crevices and from other shelters.

Biomorphological alterations induced by an anti-juvenile hormonal compound, 2-(2-ethoxyethoxy)ethyl furfuryl ether, on three species of triatominae larvae (Hemiptera, Reduviidae).

Applied topically to larvae of Rhodnius prolixus Stal, Triatoma infestans (Klug) and Panstrongylus herreri Wygodzinsky, vectors of Trypanosoma cruzi, the causative agent of Chagas' disease, a synthetic, furan-containing anti-juvenile hormonal compound, 2-(2-ethoxyethoxy)ethyl furfuryl ether induced a variety of biomorphological alterations, including precocious metamorphosis into small adultoids with adult abdominal cuticle, ocelli, as well as rudimentary adultoid wings. Some adultoids died during ecdysis and were confined within the old cuticle. The extension of these biomorphological responses is discussed in terms of the complexity of the action of anti-juvenile hormonal compounds during the development of triatomines.

Effects of azadirachtin on Rhodnius prolixus: immunity and Trypanosoma interaction.

The effects of azadirachtin, a tetranortriterpenoid from the neem tree Azadirachta indica J., on both immunity and Trypanosoma cruzi interaction within Rhodnius prolixus and other triatomines, were presented. Given through a blood meal, azadirachtin affected the immune reactivity as shown by a significant reduction in numbers of hemocytes and consequently nodule formation following challenge with Enterobacter cloacae beta 12, reduction in ability to produce antibacterial activities in the hemolymph when injected with bacteria, and decreased ability to destroy the infection caused by inoculation of E. cloacae cells. A single dose of azadirachtin was able to block the development of T. cruzi in R. prolixus if given through the meal at different intervals, together with, before or after parasite infection. Similarly, these results were observed with different triatomine species and different strains of T. cruzi. Azadirachtin induced a permanent resistance of the vector against reinfection with T. cruzi. The significance of these data is discussed in relation to the general mode of azadirachtin action in insects.

Short- and long-term effects of proallatotoxin (ethoxyprecocene II) on Rhodnius prolixus females.

Oogenesis and oviposition can be inhibited in female of Rhodnius prolixus by means of short-term experiment (first reproductive cycle) of a single dose of ethoxyprecocene II given by ingestion. The inhibition is dose-dependent as measured by oocyte growth, egg maturation and egg deposition. In a long-term experiment (second and third reproductive cycles) egg production and oogenesis can be partially or totally re-established by subsequent blood meals without ethoxyprecocene II. These findings suggest that in female R. prolixus, damage caused to corpus allatum by ethoxyprecocene II, in certain cases, is not irreversible.

Effects of precocene and azadirachtin in Rhodnius prolixus: some data on development and reproduction.

The results presented in this paper clearly indicate that precocene and azadirachtin are effective inhibitors of moulting and reproduction in the hemipteran Rhodnius prolixus. The time of application is important and only applications of these substances early in the intermoulting period cause their effects in nymphs. The inhibition of moulting is fully reversed by ecdysone therapy. Precocene and azadirachtin also affected drastically the oogenesis and egg deposition in this insect. Precocene-induced sterilization is reversed by application of juvenile hormone III. However, this hormone is unable to reverse the effect of azadirachtin on reproduction. Ecdysteroid titers in nymphs and adult females are decreased by these treatments. In vitro analysis suggest that precocene and azadirachtin may act directly on the prothoracic glands and ovaries producing ecdysteroids. Based on these and other findings the possible mode of action of these compounds on the development and reproduction of Rhodnius prolixus is discussed.

[The teratogenic and toxic effect of unsaturated short-chain fatty acids in Rhodnius prolixus]. / Efecto teratogénico y toxico de acidos grasos de cadena corta insaturados, en Rhodnius prolixus.

The teratogenic role of two short-chain unsaturated fatty acids, octinoic acid and undecylenic acid on the hemimetabolic metamorphosis of the insect Rhodnius prolixus (Hemipter) is studied. The acids penetrate through the cuticle of the abdomen and tarsi, independently of the amount of distention. The effects are registered equally in satiated or hungry insects, in those treated topically or in those where the treatment was applied to the support paper. The acids apparently do not affect the formation of the cuticle, melanization, nor the metamorphic process. The damage induced by these acids are manifested at random in the locomotor as well as the cephalic appendices, a displacement of the proboscide being observed as the dosage is increased. Octinoic acid acts as a teratogen at doses of undecylenic acid which are lethal for the insect. The malformations of the proboscide include the labium the most dramatically damaged, as well as other bucal appendages, separately or accompanying the damage to the labium. Damage in the locomotor appendages is frequently displaced to the second and third pair of legs, while the first pair is the least affected.

Effects of juvenile hormone analogue on ecdysis prevention induced by precocene in Rhodnius prolixus (Hemiptera:Reduviidae).

Precocene II, added to the meal of fourth-instar larvae of Rhodnius prolixus (25 micrograms/ml of blood), induced an increase in the duration of the molting cycle. This effect was related to the decrease of both the nuclear area of the prothoracic gland cells and the mitotic activity in epidermal cells. Juvenile hormone analogue applied topically (60 micrograms/insect) together with Precocene II treatment avoided atrophy of the prothoracic glands and induced a higher number of epidermal mitosis accelerating the time of subsequent ecdysis. A possible relationship between juvenile hormone and production of ecdysone is discussed.

[Morphogenetic effects of precocene II on nymphs of Rhodnius prolixus (Stal, 1859) (Hemiptera-Triatominae)]. / Efeitos morfogênicos de precoceno II em ninfas de Rhodnius prolixus (Stal, 1859) (Hemiptera-Triatominae)

The morphogenetic effects of Precocene II in nymphs of 1st-, 2nd-, 3rd-, and 4th-instar of Rhodnius prolixus were studied. A high number of insects underwent precocious metamorphosis by topical treatment (10-30 micrograms/insect) or adding the drug to the blood meal (25 micrograms/ml of blood). Adultoids of 4th- and 5th-instar, obtained by both treatments of 3rd- and 4th-instar, respectively, had mainly fully adult abdominal cuticle, ocelli, three segmented tarsi, rudimentary wings containing adult articulation with the thorax and deformed genitalia while adultiforms of 2nd- and 3rd-instar had very slight imaginal morphological characteristics. Topical treatment induced a high mortality in nymphs of 1st-instar and Precocene II given orally produced a high number of adultoids in this instar. The mode of application and the action of Precocene II on different nymphal instars were interpreted.