Investigation into insecticide resistance in vine mealybugs
De Wet, O
The project has revealed that potential resistance mechanisms are present in the vine mealybug (Planococcus ficus). The two resistance mechanisms tested for were insensitive acetyl cholinesterase (AChE) and enhanced carboxylesterase activity.
Colonies were reared from three different areas, namely Hex River Valley (Hex), Robertson (Rob) and Stellenbosch (Stel). The insectary colony (lab) and a table grape colony (tab) were included in the study. Chlorpyrifos was applied to individuals of different colonies in bioassays. LD50s and LD90s were determined for all populations. Data were statistically analysed.
– The Stellenbosch population had the lowest LD50 value, indicating that it was most susceptible of all populations.
– The laboratory and Robertson colonies have the same LD50 value but it is +/-1.2 times more than the LD50 value of the Stellenbosch population.
– The Hex River Valley and table grape colonies have the same LD50 value and this value is +/- 1.5 times more than the LD50 of the Stel population.
– The Hex River Valley and table grape populations, regression slopes are not parallel with laboratory and Robertson but they are significantly different from each other, as well as from the Stellenbosch population at the LD50 level.
– There is, however, no significant difference between Stellenbosch, Hex River Valley and table grape at the LD90 level.
– The conclusion is that minor differences currently occur between the susceptibility to chlorpyrifos of populations of the different areas.