Mode of Action of the Natural Insecticide, Decaleside Involves Sodium Pump Inhibition.

Yallappa Rajashekar,Thimmappa Shivanandappa,Frederic Marion-Poll

doi:10.1371/journal.pone.0170836

Abstract

Decalesides are a new class of natural insecticides which are toxic to insects by contact via the tarsal gustatory chemosensilla. The symptoms of their toxicity to insects and the rapid knockdown effect suggest neurotoxic action, but the precise mode of action and the molecular targets for decaleside action are not known. We have presented experimental evidence for the involvement of sodium pump inhibition in the insecticidal action of decaleside in the cockroach and housefly. The knockdown effect of decaleside is concomitant with the in vivo inhibition of Na+, K+ -ATPase in the head and thorax. The lack of insecticidal action by experimental ablation of tarsi or blocking the tarsal sites with paraffin correlated with lack of inhibition of Na+- K+ ATPase in vivo. Maltotriose, a trisaccharide, partially rescued the toxic action of decaleside as well as inhibition of the enzyme, suggesting the possible involvement of gustatory sugar receptors. In vitro studies with crude insect enzyme preparation and purified porcine Na+, K+ -ATPase showed that decaleside competitively inhibited the enzyme involving the ATP binding site. Our study shows that the insecticidal action of decaleside via the tarsal gustatory sites is causally linked to the inhibition of sodium pump which represents a unique mode of action. The precise target(s) for decaleside in the tarsal chemosensilla and the pathway linked to inhibition of sodium pump and the insecticidal action remain to be understood.

Highlights

In view of the environmental and ecological concerns, human health hazards, and increasing insect resistance, many insecticides have been banned or replaced by newer chemicals [1]
A preliminary observation in our study we found in vivo inhibition of Na+, K+ -ATPase in decaleside-treated insects, which led to the present study wherein we present experimental evidence that Na+, K+ -ATPase is involved in the insecticidal action of decaleside in insects, which leads us to postulate novel mode of action for these unique natural insecticides
Our study has demonstrated that Na+, K+ -ATPase is severely inhibited in insects exposed to decaleside I and II in the contact bioassay

Summary

Introduction

In view of the environmental and ecological concerns, human health hazards, and increasing insect resistance, many insecticides have been banned or replaced by newer chemicals [1]. Mode of action of the major chemical classes of insecticides involves mainly three target sites in the nervous system: acetylcholinesterase, an enzyme of critical importance in the transmission of nerve impulse (organophosphorus and carbamates), voltage-gated sodium channels across the nerve membrane (pyrethoids and DDT), and the acetylcholine receptor (neonicotinoids) [1,2,3,4,5]. Selective insecticides such as juvenile hormone mimics (fenoxycarb and pyriproxyfen), ecdysone agonists and chitin synthesis inhibitors (Diflubenzuron) act on insect-. A new class of insecticides derived from actinomycetes, show high selectivity and low mammalian toxicity with eco-friendly behaviour [18,19]

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