The Effect of Single and Combined Heat and CO2 Stimuli at Different Ambient Temperatures on the Behavior of Two Plant-Parasitic Nematodes.

Pratylenchus penetrans and Ditylenchus dipsaci were reared at 15-16 C, and their behavior towards single and combined heat and CO stimuli was studied at ambient temperatures of 8.6 and 27.3 C. At the lower temperature, attractivity of the heat source was prevalent in both species, but CO was also attractive. At the higher ambient temperature (27.3 C), the reaction to CO was more positive and more rapid than to heat. In fact, at this temperature only D. dipsaci was attracted to the heat source, whereas P. penetrans did not react positively. The combined stimulation of heat and CO caused D. dipsaci to aggregate more strongly than did a single stimulus; this applied to both ambient temperatures. For P. penetrans exposed to the low temperature (8.6 C), the combined stimuli were about as attractive as was the better of the single stimuli; i.e., heat. At the high temperature (27.3 C), the combined stimulation was less effective than the better of the single stimuli; i.e., CO. At this ambient temperature, the thermonegative reaction seems to dominate over the CO-positive one. The reaction of D. dipsaci was generally stronger in all experimental variants than that of P. penetrans. Insofar as temperature gradients play a role in locating host plant roots, their efficacy would seem to be restricted to a favorable temperature range. Within this range, combined heat and CO stimuli might improve attractivity.