Strategic approaches for applications of entomopathogenic fungi to counter insecticide resistance in agriculturally important insect pests

Abstract

Insect attack is a serious agricultural problem, both in the field and during storage, leading to substantial yield losses and reduced product quality. Annually, insect pests destroy about 25% of food crops worldwide. Intense use of insecticides in pest management systems has caused several ecological complications. Of them, the development of resistance to insecticides amongst the target insect pests is the major impediment in agricultural pest management programme. To date, more than 645 species of phytophagous insects and mite pests have developed high degree of resistance to several classes of insecticides mediated through a complex of biological and physiochemical mechanisms mediated via a complex of enzymatic induction. Resistance management strategies employing combination of insecticides or alternation of insecticides are suggested to improve the sustainability and to prevent/delay the development of resistance, but with potentialities of cross resistance between the currently approved insecticides, practical options are few. Naturally occurring insect pathogenic fungi are widely prevalent amongst insect species in diverse agroecosystems. Many species of entomopathogenic strains derived from Hyphomycetes and Zygomycetes classes have potential to control a range of pest insects with their unique contact action. Novel strategies employing myco-insecticides derived from fungi are advantageous in dealing with insecticide resistance management (IRM). The Hyphomycete species, viz. Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin, Nomuraea rileyi (Farlow) Samson, Paecilomyces fumosoroseus (Wize) Brown and Smith, Lecanicillium (=Cephalosporium = Verticillium) lecanii (Zimmermann) Viegas and Hirsutella thompsonii Fisher, and Zygomycete species, viz. Entomophthora virulenta Hall and Dunn, Erynia neoaphidis Remaudiere and Hennebert and Zoophthora radicans (Brefeld) Batko, are being employed to counter insect resistance to insecticides against diverse insect pests. Many of these fungi induce quick mortality of target pests by inhibiting enzymatic detoxification mechanisms which in turn predispose the target pest insects for fungal infection. Instances of joint application of promising isolates of fungal entomopathogens with selective insecticides have been employed against a diverse suite of pests to slash down the selection pressure to insecticides and to overcome concurrent resistance risks in target pests. Integration of promising strains of insect pathogenic fungi with selective insecticides tends to improve the pest control efficiency, besides decrease the amount of insecticides required and minimize the risks associated with hazards involved in environmental and health issues, which further render delayed expression of insecticide resistance in insect pests. This review focuses on the potentials for employing some promising stains of fungal entomopathogens for complementing existing insect pest management measures with insecticide resistance management for agriculturally important insect pests.