RESISTANCE MONITORING OF COTTON LEAF WORM, SPODOPTERA LITTORALIS (BOISDUVAL) (LEPIDOPTERA: NOCTUIDAE) AGAINST CERTAIN ALTERNATIVE INSECTICIDES OF FOUR DIFFERENT FIELD POPULATIONS IN EGYPT

Cotton leaf worm, Spodoptera littoralis (Boisd.) is a key pest
affecting many field crops and vegetables in Egypt. Its control depends
mainly on the application of various insecticides with different modes of
action. In the current study, susceptibility of four field collected
populations were tested to six insecticides for three consecutive years
(2015-2017). These insecticides included insect growth regulators (IGRs),
spinosad and emamectin benzoate. These insecticides at their variable
concentrations were tested against 2-nd instar larvae of S. littoralis under
laboratory conditions. Comparing with laboratory strain, field-collected
RESISTANCE MONITORING OF COTTON LEAF WORM320
populations showed a susceptibility to very low levels of resistance to the
tested IGRs. Resistance ratio (RR) recorded (1.23– 5.46-fold) to
lufenuron, 2.16 – 5.57-fold to flufenoxuron, 1.69 –6.78 fold to
chlorfluazuron and 0.45-2.46-fold to hexaflumuron. Furthermore,
emamectin benzoate showed very low to low level of resistance (2–10
fold), in line with spinosad which recorded 1.36 - 3.40-fold. Concerning
the cross-resistance between the tested insecticides was explored
throughout pairwise correlation analysis. The obtained data indicated a
significant correlation between the tested IGRs except for lufenuron and
hexaflumuron. In contrast, spinosad showed no correlation with all other
tested insecticides with reference to the negative correlation with
emamectin benzoate. Similarly, emamectin benzoate showed non-
significant correlation to all the tested insecticides except for
chlorfluazuron. So, rotation of insecticides with none and negative cross-
resistance can carry out effective control of the pest and sustain pest
susceptibility to recommended insecticides.