Effectiveness of cypermethrin against diamondback moth (Plutella xylostella L.) eggs and larvae on cabbage under Botswana conditions

The efficacy of cypermethrin against the diamondback moth (DBM) on cabbage was studied at Botswana College of Agriculture, Gaborone, Botswana. Using five concentrations of cypermethrin: 1.2, 1.6, 2.0, 2.4 and 2.8 g/L, bioassays were conducted against DBM eggs and second instar larvae at 30±5°C. Each treatment was replicated three times. Probit analysis was used to determine LD50 and LD90 values for the treatments against eggs and larvae. When the treatments were assessed at 48, 72 and 96 h, LD90 values against larvae were 2.01, 1.82 and 1.19 g/L, whereas they were 1.69, 1.63 and 1.40 g/L against eggs. This indicated that cypermethrin was highly effective against both eggs and larvae. The slopes of the probit lines for larvae assessed at 48, 72 and 96 h after application were 0.999, 0.995 and 0.949, while those against eggs were 0.973, 0.961 and 0.945. This indicates a rapid change in mortality with increase in pesticide dosage for both eggs and larvae. The study shows that cypermethrin can still be used to achieve effective control of DBM eggs and larvae under Botswana conditions especially when used in combination with other control methods in an integrated pest management programme.   Key words: Cypermethrin, efficacy, diamondback moth, cabbage.