Biochemical studies on different field strains of the pink bollworm Pectinophora gossypiella (Saund.) (Lepidoptera: Gelechiidae) in Egypt.

The specific activity of the esterases and the corresponding total proteins of the diapaused pink bollworm, Pectinophora gossypiella larvae taken from dry bolls which had been left in the cotton fields of the growing seasons of 2000&2001 were measured in four field strains representing the four Governorates: Alexandria, Al-Behaira , Kafr El-Shaikh, and Al-Gharbia. Parallel to these larvae the last generation of the pink bollworm moths trapped from Al-Behaira fields at the end of the same seasons were included in the comparative study. Besides, the susceptible strain larvae and moths from the Lab. of Bollworms Department at the Institute of Plant Protection, Cairo were used as a reference for comparing levels of resistance in the four bollworm strains representing the four Governorates and its impact on proteins and esterases types and activity. Gel scanning with respective standard molecular weights revealed variation in protein bands number and molecular weight type among the four tested field strains. Similarly, the sites of esterases on the SDS-PAGE proved high level of resistance reflected in appearance of isozymes, especially in Al-Gharbia field strain. Generally, Alexandria field strain showed the least level of resistance due to the limited area of cotton fields and the less use of insecticides in Alexandria fields. It is suggested that SDS-PAGE technique can be a biomarker for detection of susceptibility levels or resistance in the field strains, which should lead to a change in the currently applied chemicals. All field strains which had exposed annually to successive insecticide applications revealed an increase of protein bands and a decrease of esterases of lower molecular weight than those in the susceptible strain. Chemical insecticides are known to be able to act as inducers for the biosynthesis of cellular proteins or as inhibitors of enzymes; so, the molecular biochemical explanation of variations among the tested field strains can be attributed to either variation or similarity in the background exposure to the chemical control programs.