Several species of wireworms were attracted to germinating wheat, air from flasks of germinating wheat, decomposing oatmeal, commercial CO2 and, in addition, germinating seeds of eight other cultivated plant species. Larvae located a biological or experimental source of CO2 by a directed movement along CO2 gradients, from distances up to 20 cm.
Methods and apparatus for measuring small CO2 gradients, using gas chromatography and mass spectrometry, are described. Ctenicera destructor (Brown) larvae apparently responded to CO2 gradients between glass plates, that ascended on the average by 0.002% (soil) and 0.005% (agar)/cm over a distance of from 12 to 16 cm. The "sensitivity threshold" was calculated as being 1–2 ppm over the distance involved in one deflection of the head during klinotactic orientation. Attractancy was observed within a range of CO2 concentration from about 0.036% to 1.5%. Repellent effects did not appear to be only related to concentration, but possibly were due to steepness of the gradient and(or) previous exposure to CO2.
Passing an air stream from germinating grain over a KOH solution eliminated the attractancy of the grain by removing the CO2 and possibly other undetected attractants. A small percentage of C. destructor larvae apparently oriented to an ethylene source, but it was concluded the CO2 was the most important if not the only attractant from germinating wheat seeds.
(Received April 24 1975)
1 Contribution No. 601 of the Research Station, Saskatoon.
2 Research Station, Canada Department of Agriculture, Saskatoon, Sask., S7N 0X2.
3 Swiss Federal Research Station for Aboriculture, Viticulture and Horticulture, Wädenswil, Switzerland.