Lethal effect of a bait for Rhodnius prolixus (Hemiptera: Reduviidae), the vector of Chagas' disease, containing hexachlorocyclohexane (HCH), under laboratory conditions

The lethal effect of a bait containing an aqueous hexachlorocyclohexane (HCH) suspension at the concentration of 1g/l and maintained at room temperature was studied in the laboratory over a period of 12 weeks. The suspension was placed in a latex bag hanging inside a 1000-ml beaker tightly covered with nylon netting, and left there with no changes for 85 days. Sixteen groups of R. prolixas bugs, consisting on average of 30 specimens each, were successively exposed to the bait and observed at different intervals for one week each. The mortality rate was 100% for all groups, except for the 16th, whose mortality rate was 96.7%. As the groups succeeded one another, mortality started to occur more rapidly and was more marked at the 6- and 24-h intervals. Later tests respectively started at 6:00 a.m. and 6:00 p.m. showed that diurnal and nocturnal periodicity in the offer of food had no effect on mortality. First- and 2nd- instar nymphs and adults male were more sensitive and 5th- instar nymphs were more resistant to the active principle of the bait.

Nota sôbre a presença do Rhodnius prolixus Stal, 1859, no Estado de São Paulo, Brasil (Hemiptera, Reduviidae, Triatominae)

Através de um lote de ninfas e adultos de Rhodnius, proveniente de Mira Estrela, Estado de São Paulo, assinalamos pela p rim e ira vez, a presença de Rhodnius prolixus nesse Estado.

A resposta de Rhodnius prolixus a estímulos térmicos

Uma série de experiências com formas adultas de Rhodnius prolixus, realizadas tanto no laboratório como em recinto de dimensões mais amplas, demonstrou uma acentuada atração para fontes de calor, com um máximo de atividades em torno dos 37 graus Centígrados. Nossos estudos revelaram que o inseto percebe estímulos térmicos a uma certa distância da fonte. Embora o reconhecimento de radiações infra-vermelhas possa servir para uma orientação do triatomíneo em direção ao animal de sangue quente, não acreditamos que seja o único fator envolvido. Com a continuação de pesquisas deste gênero visa-se o aperfeiçoamento de uma técnica que se preste para o combate ao vetor.

Cytochemical study of Rhodnius neglectus and Rhodnius prolixus salivary gland cells (Hemiptera, Triatominae)

Triatomines are hematophagous bugs of medical interest in South and Central America, where they may act as invertebrate hosts of the hemoflagellate protozoa Trypanosoma cruzi (the causative of Chagas’ disease) and Trypanosoma rangeli (Tejera, 1920). Triatomines of Rhodnius genus have salivary gland formed by two close and independent units: the principal and the accessory. This gland secretes saliva that abounds in substances that facilitate and permit feeding. Despite this importance, there are few reports on its cytochemistry. In purpose of amplifying this understanding, in this work it was investigated the nuclear structures (chromatin and nucleolar corpuscles) of salivary gland cells of Rhodnius neglectus (Lent, 1954) and Rhodnius prolixus (Stål, 1859). The salivary glands were removed from adult insects, fixed and submitted to different cytochemical methods: lacto-acetic orcein, silver ion impregnation, Feulgen reaction, Toluidine Blue, Variant method of critical electrolyte concentration and C-banding. The results evidenced predominance of binucleated cells, with bulky and polyploid nucleus, decondensed chromatin and a large nucleolar area. In addition, cytoplasmic metachromasy and a clear association between nucleolar and heterochromatic corpuscles were observed. Such characteristics were associated with intense synthesis activity to produce saliva. Besides, the heterochromatic corpuscles observed with C Banding permitted the differentiation of sexes and species.

Verificação de flagelados semelhantes ao Trypanosoma rangeli Tejera, em Rhodnius prolixus alimentados em caso de doença de Chagas na Venezuela: considerações sobre a natureza deste protozoário

1) - Por inoculação do sangue de um caso agúdo de moléstia de Chagas de Zaraza, Guárico, Venezuela, em cobaia (12-11-1940), obteve-se um Schizotrypanum com caractéres morfológicos distintos dos das amostras humanas comuns do Schizotrypanum cruzi; seu índice nuclear médio varia em tôrno de 1.4 e seu comprimento total médio é de 20 -21 μ (DIAS & FREITAS). 2) - Praticando-se, em 30-6-1941, no mesmo caso, o xenodiagnóstico com Rhodnius prolixus procedentes de criação normal de laboratório, verificou-se, nos barbeiros enviados para o Rio de Janeiro e dissecados 65 dias depois da sucção no paciente, a presença de flagelados com o aspecto do Trypanosoma rangeli Tejera, ao lado de tripanosomas metacíclicos semelhantes aos de Schizotrypanum. 3) Por inoculação do conteúdo intestinal dêstes Rhodnius em résus, isolou-se uma amostra de Schizotrypanum cujas formas sanguicolas tinham os mesmos caracteres da amostra obtida por inoculação do sangue do paciente em cobaia. 4) - No tubo digestivo de Rhodnius prolixus e de outros barbeiros criados no laboratório e infectados com a amostra de Schizotrypanum isolada por xenodiagnóstico, não foram observadas as formas carcterísticas do Trypanosoma rangeli, mas apenas crítidias e tripanosomas metacíclicos aparentemente indistinguíveis dos de amostras comuns de Schizotrypanum. 5) - Diante dos fatos referidos, sugere-se a hipótese de ser o Trypanosoma rangeli um Schizotrypanum patogênico do homem em seu ciclo no transmissor intermediário, alguns de cujos aspectos evolutivos são inconstantes e aparecem em circunstâncias indeterminadas.

Studies on Trypanosoma rangeli Tejera 1920: VI. Developmental pattern in the haemolymph of Rhodnius prolixus

The morphological sequence of Trypanosoma rangeli development in the body cavity of Rhodnius prolixus is described. The metacyclic trypanosome is the product of successive division and transformation during the intra and extracellular development in the haemocoele. The significance of the early invasion of T. rangeli into the haemolymph is discussed. The epidemiological importance of the developmental pattern of T. rangeli in the vectors haemolymph and the host-response to the parasite are considered.

Efeitos morfogenicos de precoceno II em ninfas de Rhodnius prolixus (Stal, 1859) (Hemiptera - Triatominae)

Com o propósito de vir controlar os triatomíneos, vetores da doneça de Chgas, por substâncias não convencionais, analisamos a atuação e os efeitos de Precoceno II por tratamento tópico e oral em ninfas do 1º ao 4º estádio de Rhodnius prolixus. Com enfoque comparativo entre os dois tipos de aplicação, fizemos uma análise de deformações morfológicas externas, principalmente das estruturas genitais externas de ambos os sexos.

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 mug/ml of blood), induced an in crease 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 mug/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.

Efecto teratogénico y toxico de ácidos grasos de cadena corta insaturados, en Rhodnius prolixus

Se estudia el papel teratogénico de dos ácidos grasos insaturados de cadena corta, ácido octinoico y ácido undecilénico, sobre insectos de metamorfosis hemimetábola, Rhodnius prolixus (Hemiptera). La penetración de los ácidos, se realiza a través de la cutícula del abdomen y de los tarsos, se presenta como una acción independiente del grado de distensión de la misma, ya que sus efectos se registran tanto en los insectos repletos, como en los hambrientos; tanto en los tratados tópicamente como en aquellos donde la droga se aplicó al papel de soporte. Los ácidos estudiados aparentemente no afectan la formación de la cutícula, ni la melanización, como tampoco afecta el proceso de la muda. Los daños inducidos por estos ácidos se presentam al azar tanto en los apéndices locomotores como en los cefálicos, observándose un desplazamiento a la proboscide a medida que se incrementa la dosis. De las malformaciones en la proboscide, es el labio el mas dramáticamente dañado, aunque también se presentan daños en los otros apéndices bucales, aisladamente o junto con el daño del labio. El daño en los apéndices locomotores está frecuentemente desplazado al segundo y tercer par de patas, mientras que el par, fue el menos afectado. El ácido octinoico se comportó como teratogénico en las dosis que fueron letales para el insecto con el ácido undecilénico.

Efficacy of ivermectin against the bloodsucking insect, Rhodnius prolixus (Hemiptera, Triatominae)

Ivermectin (0.2 mg/kg body weight) caused a high mortality in nymphs and adults of Rhodnius prolixus following a single meal in mice sub-cutaneously injected with the drug. This effect was more evident in nymphs of 1st-and 2nd-instar than in older nymphs and adults. Third-instar nymphs presented a high mortality when fed on mice treated with ivermectin 24 and 48 hours previously, while mortality was significantly reduced in nymphs fed on mice treated 72 hours before. Surviving 3rd-instar nymphs did not molt. When adult females were fed once on mice treated for 24 hours with ivermectin there was a considerable reduction in egg production. This inhibition was not reversed by a second feeding on normal mice. We concluded that sub-lethal doses of ivermectin caused toxic effects interfering in the neuro-endocrine control of development and reproduction of this bloodsucking insect.

Mecanismo antidiurético en Rhodnius Prolixus (Stal, 1859) (Hemiptera, Reduviidae)

Se propone para R. prolixus un mecanismo antidiurético, cuya actividad se pone de manifiesto una vez transcurrido el periodo diurético y se mantiene hasta que el insecto es alimentado nuevamente. Presumiblemente este mecanismo actua a nivel del esfinter rectal proximal y es inhibido por la ingesta, distención mecanica del buche y desinhibición central por decapitación. Se sugiere que la actividad antidiurética es mantenida por vía nerviosa y se modifica cuando hay distensión del buche o canudo es interrumpida la senãl nerviosa por decapitación. Se pone de manifiesto que la excreción de orina en R. prolixus no es controlada exclusivamente por la hormona diurética, sino que factores no ligados a la hemolinfa mantienen en estado diurético y no diurético a los insectos.

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 roles of haemolymphatic lipoproteins in the oogenesis of Rhodnius prolixus

The fates of purified 32P-vitellin and 32P-lipophorin were followed in vitellogenic females of Rhodnius prolixus. While the radioactivity from 32P-vitellin 6 hours after injection was found almost exclusively in the ovary, the radioactivity from injected 32P-lipophorin was found distributed among several organs. In the ovary, the radioactivity from 32P-vitellin was associated with the contents of the yolk granules. 32P-lipophorin delivered a great amount of radioactive phospholipids to the ovary with no accumulation of its protein moiety, as observed after its iodination with 131I. The delivery of phospholipids was inhibited at 0ºC and by the metabolic inhibitors, sodium azide and sodium fluoride. Comparison of the radioactivity incorporation from 32P-lipophorin with that of 14C-inulin suggests that the 32P-phospholipids from lipophorin are not taken up by fluid phase endocytosis. The data presented here are compatible with the concept of lipophorin as a carrier of lipids in insects and provide evidence that lipophorin transports phospholipids as shown previously for other classes of lipids. The utilization by the oocytes of the phospholipids transported by lipophorin is discussed.

Inputs to the hormonal control of egg development in Rhodnius prolixus

This paper re-examines existing data on the environmental inputs governing egg production in Rhodnius prolixus. Feeding has a direct effect on egg production such that the product of the unfed weight of the female times the weight of the blood meal is a good predictor of the number of eggs produced. Mating modifies this input, so that mated females produce more eggs. Egg production is governed by the corpus allatum, and indirect evidence suggests that the number of eggs producted by a female is a function of the length of time that juvenile hormone is secreted by the corpus allatum. The input which determines the times at which the corpus allatum is switched off originates in the stretch induced by the amount of the meal remaining in the crop, modified by the matedness status of the female. The precise nature of the sensors detecting stretch is not yet clear, but the integrity of the dorsal aorta is essential to the transmission of the information. These data are related to the survival strategy for Rhodnius.