Evolution of resistance to leaf litter containing Bti toxins
Larvae selected across successive generations with toxic leaf litter
containing Bti toxins (LiTOX strain) acquired a significant level of
resistance to this material over just a few generations (Fig. 1). The
larval mortality of the selected LiTOX strain at the diagnostic dose
of 30 mg L−1 of toxic leaf litter decreased from nearly 100% to
11.7% after only 18 generations of selection. Statistical analysis
using a general linear model (GLM) revealed the significant effect
of the strain (χ2 = 127.026, df = 1, P < 0.001) and of the
generation number (χ2 = 63.382, df = 5, P < 0.001) on larval
mortality, confirming the progressive increase in resistance in the
LiTOX strain. Even after 18 generations of selection, the increase
in larval tolerance to the LiTOX strain to toxic leaf litter had not
levelled off, suggesting that the selection of resistant allele(s) was
incomplete and that a higher resistance level can be obtained over further generations of selection. After 18 generations of selection,
the resistance ratio (RR50) of the LiTOX strain to toxic leaf litter was
3.4-fold higher than the resistance level of the susceptible strain
Bora-Bora (Table 1).