Movement of Rotylenchulus reniformis through sand and agar in response to temperature, and some observations on vertical descent

The movement of vermiform stages of Rotylenchulus reniformis in response to a temperature gradient of 1°C per cm was investigated in 4 cm diam tubes containing 0.75% water agar or moist sand graded to 150-250 μm and 250-425 μm particle sizes. Nematodes previously stored at 30°C exhibited a temperature preferendum, or eccritic temperature, of 30°C and nematodes stored at 17°C exhibited a preferendum of 23°C in both matrices. In sand of 250-425 μm particle size, most nematodes moved 10 cm downward within 17 h. Rapid downward movement occurred regardless of moisture content or moisture gradient direction. Only living nematodes moved downward and 90% of 1,000 live nematodes that were videotaped as they descended in a narrow channel of water descended in a head downward postition.