Physiological and Morphological Aspects of Aedes aegypti Developing Larvae: Effects of the Chitin Synthesis Inhibitor Novaluron

Abstract

Population control of the dengue vector mosquito, Aedes aegypti, is difficult due to many reasons, one being the development of resistance to neurotoxic insecticides employed. The biosynthesis of chitin, a major constituent of insect cuticle, is a novel target for population control. Novaluron is a benzoylphenylurea (BPU) that acts as a chitin synthesis inhibitor, already used against mosquitoes. However, information regarding BPU effects on immature mosquito stages and physiological parameters related with mosquito larval development are scarce. A set of physiological parameters were recorded in control developing larvae and novaluron was administered continuously to Ae. aegypti larvae, since early third instar. Larval instar period duration was recorded from third instar until pupation. Chitin content was measured during third and fourth instars. Fourth instars were processed histochemically at the mesothorax region, stained with hematoxylin and eosin (HE) for assessment of internal tissues, and labeled with WGA-FITC to reveal chitinized structures. In control larvae: i) there is a chitin content increase during both third and fourth instars where late third instars contain more chitin than early fourth instars; ii) thoracic organs and a continuous cuticle, closely associated with the underlying epidermis were observed; iii) chitin was continuously present throughout integument cuticle. Novaluron treatment inhibited adult emergence, induced immature mortality, altered adult sex ratio and caused delay in larval development. Moreover, novaluron: i) significantly affected chitin content during larval development; ii) induced a discontinuous and altered cuticle in some regions while epidermis was often thinner or missing; iii) rendered chitin cuticle presence discontinuous and less evident. In both control and novaluron larvae, chitin was present in the peritrophic matrix. This study showed quantitatively and qualitatively evidences of novaluron effects on Ae. aegypti larval development. To our knowledge, this is the first report describing histological alterations produced by a BPU in immature vector mosquitoes.

Physical features and chitin content of eggs from the mosquito vectors Aedes aegypti, Anopheles aquasalis and Culex quinquefasciatus: Connection with distinct levels of resistance to desiccation

“…This labeling procedure has been previously employed to identify chitin in Ae. aegypti serosal and larval cuticles (Rezende et al, 2008;Farnesi et al, 2012) and in Anopheles gambiaeserosal cuticle (Goltsev et al, 2009). Beyond detection of chitin in all samples (Fig.…”

“…Chitin was quantified through its glucosamine derivatives obtained after deacetylation, depolymerization and deamination of the N-acetylglucosamine polymer (Lehmann and White, 1975;Zhang and Zhu, 2006;Farnesi et al, 2012). Briefly, triturated eggshells underwent an alkaline digestion that deacetylates chitin, converting it into chitosan, a glucosamine polymer.…”

Chitin synthesis inhibitors: old molecules and new developments

“…Can be used in tropical areas also in rainy seasons (Ishaaya, 2001). Insecticidal effects on developing larvae of Aedes aegypti (Farnesi et al, 2012). Ishaaya et al, 1996 Flufenoxuron Acaricide, which is most effective against spidermites and plant lice; used to treat stone fruits, pome fruits, and grapevines.…”

Triflumuron Effects on the Physiology and Reproduction ofRhodnius prolixusAdult Females

“…TFM is nowadays used against both stored products pests and disease vectors [38–48], strongly affecting insect reproduction by disruption of oviposition and/or eclosion of eggs laid by treated females. Its ovicidal effect is achieved either by direct application onto eggs [39, 49, 50] or by treatment of insects at any life stage [25, 51–53].…”