Biochemical Insecticide Resistance in Tea Pests

Abstract

Polyphagous insect herbivores encounter numerous toxins (xenobiotics) as they pass through their life cycle; some toxins are produced naturally by the host plants (allelochemicals) and others by humans (insecticides) to manage these insects having pest status. The host plants have evolved defensive mechanisms for protection from herbivory, including chemical repellents and toxins (secondary metabolites). Many classes of insect repellents and toxic substances, such as isoflavonoids, furanocoumarins, terpenoids, alkaloids and cyanogenic glycosides are synthesized in plants. The biosynthetic pathways leading to these allelochemicals are continually evolving to generate new secondary metabolites. Similarly, to control the herbivorous insect pests, numerous chemicals of synthetic origin are used continuously against them. In response, the attacking organisms also evolve mechanisms that enable them to resist the defensive chemicals of their hosts and those toxins of synthetic origin applied for their control. A variety of defence mechanisms, including enzymatic detoxification systems, physiological tolerance and behavioural avoidance, protect insect herbivores from these xenobiotic compounds. Insect pests have evolved the mechanisms to degrade metabolically (enzymatically) or otherwise circumvent the toxic effect of many types of chemicals that we have synthesized as modern insecticides. The extent to which insects can metabolize and thereby degrade these antibiotics or toxins is of considerable importance for their survival in hostile chemical environment. These mechanisms continue to evolve as insects attempt to colonize new plant species or encounter newer molecules of synthetic insecticides. Generally, three main enzymes, general esterases (GEs), glutathione Stransferases (GSTs) and cytochrome P450-mediated monooxygenases (CYPs), are involved in the process of metabolic detoxification of insecticides. During the past 70 years, following the discovery and extensive use of synthetic insecticides, resistance of insects to insecticides has registered the greatest increase and strongest impact. The evolution of resistance to insecticides is an example of evolutionary process. An insecticide is the selection pressure, which results in a very strong but differential fitness of the individual in a population having susceptible and resistant genotypes. The survival and subsequent reproduction of resistant individuals lead to a change in the frequency of alleles conferring resistance in the population over

Gene selection for studying frugivore-plant interactions: a review and an example using Queensland fruit fly in tomato

“…The P450s contribute to the catalysis of numerous oxidative reactions during endogenous and exogenous metabolism (Li & Liu, 2019). (Berenbaum & Johnson, 2015;Saha, 2016).…”

“…Phase I and Phase II involve metabolizing enzymes altering toxic chemicals, while Phase III involves transport and export of conjugated metabolites and elimination of toxins pre-biotransformation. The major gene families associated with each phase are followed: CYP450, Cytochrome P450; EST, Carboxylesterase; GST, Glutathione S-transferase; UGT, UDP-Glucosyltransferase; MDR, Multidrug Resistance Protein; MRP, Multidrug Resistance Associated Protein; ABC, ATP Binding Cassette(Berenbaum & Johnson, 2015;Saha, 2016).Full-size DOI: 10.7717/peerj.11762/fig-3…”