Nerve Insensitivity to Cypermethrin in Field and Laboratory Strains of Heliothis Virescens

R. T. Gladwell, A.R. McCaffery, and C.H. Walker


Nerve insensitivity to synthetic pyrethroid insecticides has been reported in resistant strains of Heliothis virescens. A rapid and robust method was developed for monitoring nerve insensitivity in laboratory and in field-collected strains. The effect of cis-cypermethrin on the spontaneous multiunit activity of nerves from third instar was measured. The neural response to cypermethrin was examined in one susceptible (BRC) and in four resistant strains of H. virescens in a 'cumulative dose response, assay protocol. Preparations were exposed for successive 5 min intervals to increasing concentrations of cypermethrin (10-9, 5.10-9, 10-8, 5.10-8, and 10-7M). The concentration at which neuronal hyperactivity occurred was recorded. With one exception all the susceptible larvae responded to 10-7M, the lowest concentration of pyrethroid used. Larvae of the resistant strains had a more variable response. In the laboratory-derived resistant strain (PEG87), 33% of the larvae also displayed neuronal hyperactivity at 10-7M, but a further 28% either failed to respond at all or only responded at 10-7M, the highest concentration used. A significant proportion of the larvae of the field strains also only responded to the highest concentrations of cypermethrin or not at all, though the degree of insensitivity varied between strains. Thus the proportion of larvae which only responded at 10-7M or higher was 20% for the HN strain, 35% for the SK strain and 80% for the D strain. This study demonstrated clear differences in the sensitivity of the nervous system of susceptible and of resistant strains of H. virescins to cis-cypermethrin. Nerve insensitivity was present to some extent in all three field strains tested, though both the degree and incidence varied between strains.

Reprinted from 1990 Proceedings: Beltwide Cotton Production Research Conferences pp. 173 - 177
©National Cotton Council, Memphis TN

[Main TOC] | [TOC] | [TOC by Section] | [Search] | [Help]
Previous Page [Previous] [Next] Next Page
Document last modified Sunday, Dec 6 1998