PYRETHROID RESISTANCE INCREASING IN UNSPRAYED POPULATIONS OF HELICOVERPA-ARMIGERA (HUBNER) (LEPIDOPTERA, NOCTUIDAE) IN NEW-SOUTH-WALES 1987-90

Pyrethroid resistance frequencies were determined in unsprayed Helicov erpa armigera populations collected al sites 300-400 km from northern NSW cotton growing areas. Results confirmed a gradual loss of pyrethro id susceptibility in the unsprayed populations. At the conclusion of t he survey, the frequency of resistant H. armigera was greater than 50% . These resistance frequencies are very similar to those found in spra yed H. armigera populations from cotton areas. Untreated H. armigera o bviously cannot greatly suppress resistance build-up in cotton populat ions by supplying migrants from a susceptible gene pool. Resistant mot hs must readily disperse between sprayed and unsprayed areas.