Seasonal Feeding of Larvae of Ctenicera destructor and Hypolithus bicolor (Coleoptera: Elateridae) on Potatoes Placed in the Field at Weekly Intervals1

Abstract

At Saskatoon, Saskatchewan, over 98% of the tunnels in potatoes, placed in the top 6 inches of soil for 1-week periods during the growing season, were caused by larvae of Ctenicera destructor (Brown) even though about 25% of the total population was Hypolithus bicolor Eschscholtz. Numbers of larvae of C. destructor decreased from early spring until late June or early July, mainly from mortality, and then increased with the appearance of newly hatched larvae. There was a further mortality of larvae from September to mid-October. The majority of larvae were in the top 6 inches of soil during the season, and not more than 5% were in the bottom 9- to 12-inch layer. Numbers of tunnels in the potatoes increased in general with rising soil temperatures in the spring, to a peak in early or mid-June. Alternate depressions and peaks followed, with peaks occurring in early or mid-July and early or mid-August, the last being the greatest. Tunneling then fell off to a low level by early or mid-September. Depressions in tunneling in mid-summer and after early fall were associated with low soil moisture and/or reduced temperatures, but the relationship between tunneling and concurrent soil temperature and moisture appeared to be different at different times of the season. It is suggested that previous food consumption and acclimation temperatures and moistures may influence this relationship, and that general molting of the larvae might bring about peaks and depressions of feeding at certain times. The possible importance of food plants in the fall to larval survival is discussed.