Abstract
1. The infective stage juveniles of Neoaplectana carpocapsae, a parasitic nematode of insects, was found to aggregate at point sources heated to temperatures of only 0.3°C or less above ambient in either light or dark conditions. 2. The nematode also aggregated in response to heat conducted from a wax moth larva (about 0.3°C above ambient) in the absence of CO2 or chemical gradients. 3. The responses to heat sources (1° above ambient) occurred over a wide range of ambient temperatures. 4. The apparent response of the nematode to light is at least in part caused by effects of heat from light absorption by the agar medium and nematode. 5. The response to temperature appears to function in host location especially at close range from (within a few mm) the insect.