Monitoring of resistance in Spodoptera exigua (Lepidoptera: Noctuidae) from four districts of the Southern Punjab, Pakistan to four conventional and six new chemistry insecticides

Abstract

The present studies were carried out to evaluate resistance in Pakistani populations of beet armyworm, Spodoptera exigua (Hubner) to various insecticides. Different field populations of S. exigua from four districts of the Punjab were monitored from 2008 to 2010 for resistance against insecticides using a standard leaf dip bioassay method. For pyrethroids and organophosphates, resistance ratios compared with a susceptible Lab-Pk population were in the range of 7–105-fold for deltamethrin, 12–136-fold for cypermethrin, 20–134-fold for chlorpyrifos and 37–143-fold for profenofos. For new chemistry insecticides, resistance levels were 3–73-fold for spinosad, 5–226-fold for abamectin, 6–88-fold for indoxacarb, 3–75-fold for emamectin benzoate, 2.4–59-fold for lufenuron and 3–41-fold for methoxyfenozide. The pairwise correlation coefficients of LC 50 values indicated a positive correlation with cross-resistance among deltamethrin, cypermethrin and chlorpyrifos, whereas resistance to profenofos showed correlations with resistances to other insecticides except chlorpyrifos. The new chemistry insecticides showed no correlations among any of the tested insecticides. There were high to very high levels of resistance to organophosphates in most of the populations, which suggested that these should be avoided against this pest. Selective use of pyrethroids in some areas including Multan and Khanewal, where they showed a low level of resistance, would appear to be acceptable. The new chemistry insecticides; lufenuron, methoxyfenozide, indoxacarb and emamectin had no, very low, low and moderate resistance levels for most of the tested populations, respectively. These are also considered to be environmentally safe and safer to natural enemies. Due to these characteristics they could be used in IPM programs supplemented with bio-control agents such as Nuclear Polyhedrosis Virus (NPV), and natural enemies such as parasitoids and predators. Rotation of insecticides with different mode of action where populations have no, very low or low levels of resistance could also be helpful in the management of insecticide resistance in S. exigua.