THE ORIENTATION RESPONSE OF CTEMCERA DESTRUCTOR AND OTHER WIRE WORMS (COLEOPTERA: ELATERIDAE) TO GERMINATING GRAIN AND TO CARBON DIOXIDE

Abstract

Several species of wireworms were attracted to germinating wheat, air from flasks of germinating wheat, decomposing oatmeal, commercial CO ₂ and, in addition, germinating seeds of eight other cultivated plant species. Larvae located a biological or experimental source of CO ₂ by a directed movement along CO ₂ gradients, from distances up to 20 cm.

Methods and apparatus for measuring small CO ₂ gradients, using gas chromatography and mass spectrometry, are described. Ctenicera destructor (Brown) larvae apparently responded to CO ₂ 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 CO ₂ 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 CO ₂.

Passing an air stream from germinating grain over a KOH solution eliminated the attractancy of the grain by removing the CO ₂ and possibly other undetected attractants. A small percentage of C. destructor larvae apparently oriented to an ethylene source, but it was concluded the CO ₂ was the most important if not the only attractant from germinating wheat seeds.