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

Abstract

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.

Biological factors involving Trypanosoma cruzi life cycle in the invertebrate vector, Rhodnius prolixus

“…Along with the inhibitory effect on moulting, azadirachtin also prolongs the duration in the stage followed by death (Garcia et al 1984b(Garcia et al , 1990. Garcia et al (1986bGarcia et al ( , 1987 described that the sensitive period to azadirachtin in R. prolixus is coincident with the head critical period (HCP), i.e., the period that the insect´s brain is essential for inducing the moulting (for details see Garcia et al 1990). Clearly, azadirachtin decreases the ecdysteroid levels in the hemolymph (Garcia et al 1986b(Garcia et al , 1987 and blocks synthesis of the new cuticle, which is dependent on the ecdysteroid hormones (Garcia et al 1986a).…”

“…Garcia et al (1986bGarcia et al ( , 1987 described that the sensitive period to azadirachtin in R. prolixus is coincident with the head critical period (HCP), i.e., the period that the insect´s brain is essential for inducing the moulting (for details see Garcia et al 1990). Clearly, azadirachtin decreases the ecdysteroid levels in the hemolymph (Garcia et al 1986b(Garcia et al , 1987 and blocks synthesis of the new cuticle, which is dependent on the ecdysteroid hormones (Garcia et al 1986a). As a consequence of these facts ecdysial stasis as induced by azadirachtin is reversed by treatment of R. prolixus larvae with ecdysone (Garcia & Rembold 1984).…”

“…As a consequence of these facts ecdysial stasis as induced by azadirachtin is reversed by treatment of R. prolixus larvae with ecdysone (Garcia & Rembold 1984). Interestingly, in vitro experiments indicated that only high concentration of azadirachtin directly affects the production of ecdysteroids by the prothoracic glands in vitro (PGs) but physiological dose does not (Garcia et al 1987). Therefore, we postulated that azadirachtin diminishes the production of prothoracicotropic hormone (PTTH, brain hormone) that stimulates the production of ecdysteroids rather than affects directly ecdysteroid synthesis in the PGs.…”

“…Thus, they suggested that larvae of R. prolixus treated with azadirachtin decreases the synthesis and release of PTTH, consequently affecting ecdysteroid production in the PGs (Garcia et al 1990). All these facts imply that the insect is not able to ecdysis to the next instar (Garcia et al 1984b(Garcia et al , 1986b(Garcia et al , 1987.…”

Antimoulting Activity of Eremanthus erythropappus (DC.) MacLeisch

“…More than 2000 plant species are already known to have metabolites with insecticide properties like pyrethrum, rotenone and nicotine (Balandrin 1985;rawls 1986;sukumar et al 1991). Phytochemicals endowed with hormonal, anti-hormonal (Garcia et al 1987) or toxic activities are potential agents for insect control (Bowers et al 1976, Bowers 1984, noGueira et al 2009). Alternatives may be found among natural sources, mainly higher plants that afford a number of repellent and secondary toxic metabolites (suBrahmanyam 1990).…”