Detection and Mechanisms of Resistance in Heliothis Virescens

A.R. McCaffery, E.J. Little, R.T. Gladwell, G.J. Holloway, and C.H. Walker


 
ABSTRACT

Using Heliothis virescens a range of insecticide bioassays was compared. The first instar foliar residue test was the most effective to discriminate between resistant and susceptible strains. The dip test was comparatively ineffective. The topical test produced reliably similar, moderate levels of tolerance throughout development. The adult vial test was less effective and male insects were less tolerant than females. In the resistant strain a penetration resistance delayed the entry of topically applied (14)C-cypermethrin into third instar larvae. The rapid elimination of radiolabel from the larvae in the faeces suggests a high metabolic turnover of the pyrethroid. Evidence from metabolic and conjugation studies suggests that enhanced monooxygenase activity is a major mechanism of resistance in these insects. Esterases are probably of only minor importance in pyrethroid resistance in this strain. Synergism studies suggest that monooxygenase inhibitors like piperonyl butoxide can considerably synergise the action of the synthetic pyrethroids against H. virescens. Neurophysiological studies suggest that some, but not all larvae of the resistant strain exhibit nerve-insensitivity to trans-cypermethrin, and that the extent of this insensitivity is also variable. Further experimentation indicates that this nerve insensitivity closely fits a normal distribution.



Reprinted from Proceedings: 1989 Beltwide Cotton Research Conferences pp. 207 - 211
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998