In vitro testing for nonfumigant-nematicide resistance in Heterodera schachtii

The in vitro response to touch stimulus tests the immediate capacity of a nematode to cope with immersion in nonfumigant nematicide solutions. Behavioral characteristics exhibited n this immediate reaction may be distinguished from those of longer-term trials involving growth, development and reproduction. Larvae of unstressed Heterodera schachtii populations and others stressed with carbofuran, oxamyl, phenamiphos or aldicarb were immersed in nematicide solutions. The oxamyl-stressed population was the only one indicating a significant loss of responsiveness. Protection was generally observed in stressed populations with few exceptions. Correlation of in vitro tests with greenhouse trial results was poor. A high proportion of H. schachtii retained the ability to respond to touch whether wild or stressed, after exposure to nonfumigant nematicide concentrations approaching 0.1 O/O for 24 hours. The existence of cross-tolerance or cross-resistance is strong presumptive evidence for a common biological site of action for these nematicides; however, the high proportion of H. schachtii larvae exhibiting moderate activity in the touch test suggests that the four nonfumigant nematicides employed in these experiments are inefficient nematode acetylcholinesterase inhibitors. RESUME Test in vitro de la résistance d’Heterodera schachtii aux nématicides non-fumigants La réaction, in vitro, aux stimuli de contact indique si un nématode est immédiatement capable de surmonter une immersion dans des solutions de nématicides non fumigants. Les caractéristiques comportementales liées à cette réaction doivent être distinguées de celles caractérisant les essais à long terme, ceux-ci impliquant croissance, développement et reproduction. Des larves