Cadherin-based resistance to Bacillus thuringiensis cotton in hybrid strains of pink bollworm: fitness costs and incomplete resistance.
Recessive resistance to Bacillus thuringiensis (Bt) cotton, Gossypium hirsutum L., in laboratory-selected strains of pink bollworm, Pectinophora gossypiella (Saunders), is associated with three resistance alleles (r1, r2, and r3) of a cadherin gene. Previous experiments based on measurement of fitness components in Bt-resistant and Bt-susceptible strains revealed that fitness costs and incomplete resistance are associated with resistance. Here, we used two hybrid strains of pink bollworm, each containing a mixture of susceptible and resistant individuals, and polymerase chain reaction (PCR) amplifications to test the association between cadherin genotype and fitness components for individuals sharing a common genetic background. All survivors on Bt cotton had two r alleles, confirming that recessive cadherin alleles are tightly linked with resistance to Bt cotton. On non-Bt cotton, significantly greater developmental time for rr than ss larvae indicated a recessive fitness cost, but costs did not affect survival or pupal weight. Incomplete resistance was manifested as longer developmental time, lower survival, and smaller pupal weight in rr individuals developing on Bt cotton compared with non-Bt cotton. As in previous experiments, no significant variation in performance on Bt cotton was detected among rr genotypes. However, a meta-analysis of data from seven experiments revealed that survival on Bt cotton relative to non-Bt cotton was lower in r2r3 and higher in r1r2 compared with the other rr genotypes. Assessment of fitness components associated with cadherin genotypes in hybrid strains of pink bollworm confirms that recessive resistance to Bt cotton is associated with recessive fitness costs and incomplete resistance.
Carrière
Yves
Y
Department of Entomology, 410 Forbes Building, P.O. Box 210036, Tucson, AZ 85721-0036, USA. ycarrier@ag.arizona.edu
Ellers-Kirk
Christa
C
Biggs
Robert W
RW
Nyboer
Megan E
ME
Unnithan
Gopalan C
GC
Dennehy
Timothy J
TJ
Tabashnik
Bruce E
BE
D000818:Animals; D001413:Bacillus thuringiensis; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics*; D001427:Bacterial Toxins / Q000235:genetics*; D015820:Cadherins / Q000235:genetics*; D002678:Chimera / Q000235:genetics*; D004731:Endotoxins / Q000235:genetics*; D003368:Gossypium / Q000235:genetics*; D006460:Hemolysin Proteins / Q000235:genetics*; D007305:Insecticide Resistance / Q000235:genetics*; D009036:Moths / Q000235:genetics*; D010572:Pest Control, Biological / Q000379:methods; D030821:Plants, Genetically Modified
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D015820:Cadherins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis