Esterase activity in populations of the whitefly, Bemisia tabaci (Homoptera: Aleyrodidae): Heritability and associated organophosphorus insecticide resistance

The association of esterase (EST) activity with resistance to the organophosphorus (OP) insecticide methidathion was investigated in field-collected populations of whitefly (Bemisia tabaci (Gennadius)) in Israel. The inheritance of EST activity was studied by controlled crosses in the laboratory. Among-family variance of EST activity was highly significant although all families were maintained in the same rearing room. This indicates that genetic or common environmental effects due to rearing each family on a different caged plant must have been important. Heritability estimated from son-mother regression was h²=0.98, but this estimate seems to be unrealistically high. Daughter-mother and daughter-mid-parent regressions produced lower heritability estimates (as expected). None of the regression coefficients of daughters on mother, however, were significantly different from zero and the regression on parent explained only very small amounts of the activity variation in the offspring. Estimates obtained from intraclass correlations among offspring were higher and outside the acceptable range, reflecting the variance component due to the common environment. The predictive value of the heritability estimates appears to be very low. The frequency distribution of activity among individuals sampled from one insecticide treated site (AM) was skewed to the right, as previously reported. But samples from another site (TZ) showed a symmetrical distribution, unlike the previous pattern. When field collected individuals from AM were released on clean plants in the laboratory, samples taken from the plants one or more days later showed symmetrical EST distribution. Electro-phoretic paterns of field and laboratory samples were the same, but band intensity was stronger in samples from laboratory populations. Differences in mean EST activity between populations and sampling years were unrelated to methidathion resistance.