Mutation (G275E) of the nicotinic acetylcholine receptor α6 subunit is associated with high levels of resistance to spinosyns in Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae).
The tomato leafminer, Tuta absoluta, now a major pest of tomato crops worldwide, is primarily controlled using chemical insecticides. Recently, high levels of resistance to the insecticide spinosad have been described in T. absoluta populations in Brazil. Selection of a resistant field-collected strain led to very high levels of resistance to spinosad and cross-resistance to spinetoram, but not to other insecticides that target the nicotinic acetylcholine receptor (nAChR). In this study the mechanisms underlying resistance to spinosad were investigated using toxicological, biochemical and molecular approaches. Inhibition of metabolic enzymes using synergists and biochemical assessment of detoxification enzyme activity provided little evidence of metabolic resistance in the selected strain. Cloning and sequencing of the nAChR α6 subunit from T. absoluta, the spinosad target-site, from susceptible and spinosad-resistant strains were done to investigate the role of a target-site mechanism in resistance. A single nucleotide change was identified in exon 9 of the α6 subunit of the resistant strain, resulting in the replacement of the glycine (G) residue at position 275 observed in susceptible T. absoluta strains with a glutamic acid (E). A high-throughput DNA-based diagnostic assay was developed and used to assess the prevalence of the G275E mutation in 17 field populations collected from different geographical regions of Brazil. The resistant allele was found at low frequency, and in the heterozygous form, in seven of these populations but at much higher frequency and in the homozygous form in a population collected in the Iraquara municipality. The frequency of the mutation was significantly correlated with the mortality of these populations in discriminating dose bioassays. In summary our results provide evidence that the G275E mutation is an important mechanism of resistance to spinosyns in T. absoluta, and may be used as a marker for resistance monitoring in field populations.
Departamento de Agronomia - (Entomologia), Universidade Federal Rural de Pernambuco, 52171-900 Recife, PE, Brazil.
Wellington M
WM
Silva
Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden AL5 2JQ, United Kingdom.
Madeleine
M
Berger
College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK.
Chris
C
Bass
Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden AL5 2JQ, United Kingdom.
Martin
M
Williamson
Departamento de Microbiologia, Aggeu Magalhães - FIOCRUZ, 50732-970 Recife, PE, Brazil.
Danielle M N
DM
Moura
Departamento de Agronomia - (Entomologia), Universidade Federal Rural de Pernambuco, 52171-900 Recife, PE, Brazil.
Lílian M S
LM
Ribeiro
Departamento de Agronomia - (Entomologia), Universidade Federal Rural de Pernambuco, 52171-900 Recife, PE, Brazil. Electronic address: herbert.siqueira@ufrpe.br.
Herbert A A
HA
Siqueira
D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D004338:Drug Combinations; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology*; D009036:Moths / Q000201:enzymology / Q000235:genetics*; D011978:Receptors, Nicotinic / Q000235:genetics*
D004338:Drug Combinations; D007306:Insecticides; D018942:Macrolides; D011978:Receptors, Nicotinic; C104518:nicotinic receptor alpha6; C415329:spinosad
Insecticide resistance; Metabolism; Target-site alteration; Tomato leafminer; nACh receptor