Assessment the resistance levels in field strain of cotton leafworm to some insecticides

الملخص EN

This study was performed to assess the resistance levels in a cotton leafworm (CLW), Spodoptera littoralis (Boisd) field strain in comparison with a laboratory strain toward alpha-cypermethrin, chlorpyrifos, methoxfenozide, chlorantraniliprole, and chlorfluazuron.

Their Ovicidal activity and residual toxicity against neonates were also evaluated.

Glutathione S-transferases (GST) and total esterases activities of of 2^nd and 4^th larval instars treated with these insecticides were determined.

The field strain exhibited different level of resistance where cypermethrin, chlorpyrifos, and methoxfenozide ratios (RR) were 12.7, 48.0, and 13.8, respectively for 2^nd instar, while 4^th instar is only resistant to cypermethrin, chlorpyrifos with RR of 120.8 and 19.0 compared to lab strain.

Concerning the ovicidal and residual toxicity at the recommended field rate, cypermethrin, chlorpyrifos, chlorantraniliprole, and chlorfluazuron achieved mortality of treated eggs and neonates of lab strain 95.3, 98.9, 93.3, and 96.8% , respectively as well as 75.6, 70.0, 85.2 and 91.6% , respectively against field strain.

However, methoxyfenozide showed a non-significant difference between lab and field strains.

GST and esterases activities were significantly higher in the field strain compared with that of lab strain.

It can be concluded that monitoring of insecticide resistance is a crucial step for the plant protection and resistance management programs.