Effect of Novaluron – a Chitin Synthesis Inhibitor

The Mosquito Aedes aegypti is holometabolous insect which possesses a life cycle of four stages: egg, four larval instars, pupa and adult. This is an important vector of arboviruses such as dengue fever, urban yellow fever and chikungunya. This mosquito is fundamentally aquatic and reaches the terrestrial environment only when it turns an adult. In their post-embryonic life mosquitoes like all other insects have their bodies covered with an integument which is composed of an innermost epidermal monolayer and an outermost cuticle which is a complex extracellular matrix. Proper growth and development after the hatching of the egg requires periodic molting which begins with the apolysis.

This is followed by the production of a new cuticle and ends with ecdysis which is the shedding of the old cuticle. Concerning the control of Aedes aegypti in addition to the recommended methods of mechanically eliminating the breeding site, the permanent recipients who cannot be easily discarded are treated with chemical insecticides. These compounds target the central nervous system of the insect. neurotoxic insecticides insecticide were intensively used for decades but it eventually lost effectiveness as several vector populations acquired resistance against it. Therefore, novel substances which have different target sites have been evaluated for the control of Aedes aegypti as well as other arthropod vectors and agricultural pests.

There have been many advances in the studies regarding the cuticle and processes (physiological and biological) related to it still literature about this topic is limited when it is compared to the current description of other aspects of insect biochemistry and physiology. Insect larvae when get exposed to inhibitors of chitin synthesis like benzoylphenylureas (BPUs) develop fragile cuticles which are not able to support the increases tension during the process of molting. Such larvae find it difficult to shed their exuviae and then die of starvation, suffocation or because of rupture of the weak and malformed cuticle.

BPU diflubenzuron and other Insect Growth Regulators have been recommended by WHO Pesticide Evaluation Scheme (WHOPES) for the use against aquatic mosquito stages. The methodology that is adopted for histochemical fixation and processing was able to preserve the exoskeleton and internal structures in both conditions tested (control and EI99). Administration of Novaluron interfered with the cuticle structure and showed a rope like aspect in some regions. It was also able to alter the presence of chitin in some regions of cuticle. Novaluron affects the epidermis and also other internal organs of the larvae.

Effect of Novaluron – a Chitin Synthesis Inhibitor
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