Distinguishing between inactivated and dead second stage juveniles of Meloidogyne incognita using the NaOH method

The ability to distinguish inactivated nematodes from dead ones is sometimes difficult because of their immobile. We tested whether the NaOH method could be applied to distinguish second stage juveniles (J2s) of the root-knot nematode Meloidogyne incognita that were inactivated under different conditions. The J2s inactivated by abamectin, a GABA agonist, or under the hypoxic conditions caused by CO2, reacted to the addition of NaOH. On the other hand, the J2s inactivated by fosthiazate, an organophosphate that causes muscle contraction, and those by NaN3, which inhibits respiration, did not react well to the NaOH treatment. However, these J2s reacted to the NaOH treatment after subsequent removal of the chemicals. The J2s inactivated by low temperature showed no reaction to the NaOH treatment. The NaOH method was demonstrated to be applicable for naturally immobilized nematodes such as the entomopathogenic nematode Steinernema litorale and the plant parasite Aphelenchoides besseyi. These results suggest that the NaOH method is applicable to distinguish between inactivated and dead nematodes but caution is warranted with regard to treatment temperature and the modes of action of the chemicals that are used.